Responding to the Return of Influenza in the United States by Applying Centers for Disease Control and Prevention Surveillance, Analysis, and Modeling to Inform Understanding of Seasonal Influenza.

We reviewed the tools that have been developed to characterize and communicate seasonal influenza activity in the United States. Here we focus on systematic surveillance and applied analytics, including seasonal burden and disease severity estimation, short-term forecasting, and longer-term modeling efforts. For each set of activities, we describe the challenges and opportunities that have arisen because of the COVID-19 pandemic. In conclusion, we highlight how collaboration and communication have been and will continue to be key components of reliable and actionable influenza monitoring, forecasting, and modeling activities.

Redirecting antibody responses from egg-adapted epitopes following repeat vaccination with recombinant or cell culture-based versus egg-based influenza vaccines.

Repeat vaccination with egg-based influenza vaccines could preferentially boost antibodies targeting the egg-adapted epitopes and reduce immunogenicity to circulating viruses. In this randomized trial (Clinicaltrials.gov: NCT03722589), sera pre- and post-vaccination with quadrivalent inactivated egg-based (IIV4), cell culture-based (ccIIV4), and recombinant (RIV4) influenza vaccines were collected from healthcare personnel (18-64 years) in 2018-19 (N = 723) and 2019-20 (N = 684) influenza seasons. We performed an exploratory analysis. Vaccine egg-adapted changes had the most impact on A(H3N2) immunogenicity. In year 1, RIV4 induced higher neutralizing and total HA head binding antibodies to cell- A(H3N2) virus than ccIIV4 and IIV4. In year 2, among the 7 repeat vaccination arms (IIV4-IIV4, IIV4-ccIIV4, IIV4-RIV4, RIV4-ccIIV4, RIV4-RIV4, ccIIV4-ccIIV4 and ccIIV4-RIV4), repeat vaccination with either RIV4 or ccIIV4 further improved antibody responses to circulating viruses with decreased neutralizing antibody egg/cell ratio. RIV4 also had higher post-vaccination A(H1N1)pdm09 and A(H3N2) HA stalk antibodies in year 1, but there was no significant difference in HA stalk antibody fold rise among vaccine groups in either year 1 or year 2. Multiple seasons of non-egg-based vaccination may be needed to redirect antibody responses from immune memory to egg-adapted epitopes and re-focus the immune responses towards epitopes on the circulating viruses to improve vaccine effectiveness.

Standard-dose versus MF59-adjuvanted, high-dose or recombinant-hemagglutinin influenza vaccine immunogenicity in older adults: comparison of A(H3N2) antibody response by prior season's vaccine status.

BACKGROUND: Annual influenza vaccination is recommended for older adults but repeated vaccination with standard-dose influenza vaccine has been linked to reduced immunogenicity and effectiveness, especially against A(H3N2) viruses. METHODS: Community-dwelling Hong Kong adults aged 65-82 years were randomly allocated to receive 2017/18 standard-dose quadrivalent, MF59-adjuvanted trivalent, high-dose trivalent, and recombinant-HA quadrivalent vaccination. Antibody response to unchanged A(H3N2) vaccine antigen was compared among participants with and without self-reported prior year (2016/17) standard-dose vaccination. RESULTS: Mean fold rise (MFR) in antibody titers from Day 0 to Day 30 by hemagglutination inhibition and virus microneutralization assays were lower among 2017/18 standard-dose and enhanced vaccine recipients with (range, 1.7-3.0) vs. without (range, 4.3-14.3) prior 2016/17 vaccination. MFR was significantly reduced by about one half to four fifths for previously vaccinated recipients of standard-dose and all three enhanced vaccines (ß range, 0.21-0.48). Among prior-year vaccinated older adults, enhanced vaccines induced higher 1.43 to 2.39-fold geometric mean titers and 1.28 to 1.74-fold MFR vs. standard-dose vaccine by microneutralization assay. CONCLUSIONS: In the context of unchanged A(H3N2) vaccine strain, prior-year vaccination was associated with reduced antibody response among both standard-dose and enhanced influenza vaccine recipients. Enhanced vaccines improved antibody response among older adults with prior-year standard-dose vaccination.

Reported Global Avian Influenza Detections Among Humans and Animals During 2013-2022: Comprehensive Review and Analysis of Available Surveillance Data.

BACKGROUND: Avian influenza (AI) virus detections occurred frequently in 2022 and continue to pose a health, economic, and food security risk. The most recent global analysis of official reports of animal outbreaks and human infections with all reportable AI viruses was published almost a decade ago. Increased or renewed reports of AI viruses, especially high pathogenicity H5N8 and H5N1 in birds and H5N1, H5N8, and H5N6 in humans globally, have established the need for a comprehensive review of current global AI virus surveillance data to assess the pandemic risk of AI viruses. OBJECTIVE: This study aims to provide an analysis of global AI animal outbreak and human case surveillance information from the last decade by describing the circulating virus subtypes, regions and temporal trends in reporting, and country characteristics associated with AI virus outbreak reporting in animals; surveillance and reporting gaps for animals and humans are identified. METHODS: We analyzed AI virus infection reports among animals and humans submitted to animal and public health authorities from January 2013 to June 2022 and compared them with reports from January 2005 to December 2012. A multivariable regression analysis was used to evaluate associations between variables of interest and reported AI virus animal outbreaks. RESULTS: From 2013 to 2022, 52.2% (95/182) of World Organisation for Animal Health (WOAH) Member Countries identified 34 AI virus subtypes during 21,249 outbreaks. The most frequently reported subtypes were high pathogenicity AI H5N1 (10,079/21,249, 47.43%) and H5N8 (6722/21,249, 31.63%). A total of 10 high pathogenicity AI and 6 low pathogenicity AI virus subtypes were reported to the WOAH for the first time during 2013-2022. AI outbreaks in animals occurred in 26 more Member Countries than reported in the previous 8 years. Decreasing World Bank income classification was significantly associated with decreases in reported AI outbreaks (P<.001-.02). Between January 2013 and June 2022, 17/194 (8.8%) World Health Organization (WHO) Member States reported 2000 human AI virus infections of 10 virus subtypes. H7N9 (1568/2000, 78.40%) and H5N1 (254/2000, 12.70%) viruses accounted for the most human infections. As many as 8 of these 17 Member States did not report a human case prior to 2013. Of 1953 human cases with available information, 74.81% (n=1461) had a known animal exposure before onset of illness. The median time from illness onset to the notification posted on the WHO event information site was 15 days (IQR 9-30 days; mean 24 days). Seasonality patterns of animal outbreaks and human infections with AI viruses were very similar, occurred year-round, and peaked during November through May. CONCLUSIONS: Our analysis suggests that AI outbreaks are more frequently reported and geographically widespread than in the past. Global surveillance gaps include inconsistent reporting from all regions and human infection reporting delays. Continued monitoring for AI virus outbreaks in animals and human infections with AI viruses is crucial for pandemic preparedness.

Immunogenicity of High-Dose Egg-Based, Recombinant, and Cell Culture-Based Influenza Vaccines Compared With Standard-Dose Egg-Based Influenza Vaccine Among Health Care Personnel Aged 18-65 Years in 2019-2020.

Background: Emerging data suggest that second-generation influenza vaccines with higher hemagglutinin (HA) antigen content and/or different production methods may induce stronger antibody responses to HA than standard-dose egg-based influenza vaccines in adults. We compared antibody responses to high-dose egg-based inactivated (HD-IIV3), recombinant (RIV4), and cell culture-based (ccIIV4) vs standard-dose egg-based inactivated influenza vaccine (SD-IIV4) among health care personnel (HCP) aged 18-65 years in 2 influenza seasons (2018-2019, 2019-2020). Methods: In the second trial season, newly and re-enrolled HCPs who received SD-IIV4 in season 1 were randomized to receive RIV4, ccIIV4, or SD-IIV4 or were enrolled in an off-label, nonrandomized arm to receive HD-IIV3. Prevaccination and 1-month-postvaccination sera were tested by hemagglutination inhibition (HI) assay against 4 cell culture propagated vaccine reference viruses. Primary outcomes, adjusted for study site and baseline HI titer, were seroconversion rate (SCR), geometric mean titers (GMTs), mean fold rise (MFR), and GMT ratios that compared vaccine groups to SD-IIV4. Results: Among 390 HCP in the per-protocol population, 79 received HD-IIV3, 103 RIV4, 106 ccIIV4, and 102 SD-IIV4. HD-IIV3 recipients had similar postvaccination antibody titers compared with SD-IIV4 recipients, whereas RIV4 recipients had significantly higher 1-month-postvaccination antibody titers against vaccine reference viruses for all outcomes. Conclusions: HD-IIV3 did not induce higher antibody responses than SD-IIV4, but, consistent with previous studies, RIV4 was associated with higher postvaccination antibody titers. These findings suggest that recombinant vaccines rather than vaccines with higher egg-based antigen doses may provide improved antibody responses in highly vaccinated populations.

Risk for Infection in Humans after Exposure to Birds Infected with Highly Pathogenic Avian Influenza A(H5N1) Virus, United States, 2022.

During February 7─September 3, 2022, a total of 39 US states experienced outbreaks of highly pathogenic avian influenza A(H5N1) virus in birds from commercial poultry farms and backyard flocks. Among persons exposed to infected birds, highly pathogenic avian influenza A(H5) viral RNA was detected in 1 respiratory specimen from 1 person.

Effect of Repeat Vaccination on Immunogenicity of Quadrivalent Cell-Culture and Recombinant Influenza Vaccines Among Healthcare Personnel Aged 18-64 Years: A Randomized, Open-Label Trial.

BACKGROUND: Antibody responses to non-egg-based standard-dose cell-culture influenza vaccine (containing 15 µg hemagglutinin [HA]/component) and recombinant vaccine (containing 45 µg HA/component) during consecutive seasons have not been studied in the United States. METHODS: In a randomized trial of immunogenicity of quadrivalent influenza vaccines among healthcare personnel (HCP) aged 18-64 years over 2 consecutive seasons, HCP who received recombinant-HA influenza vaccine (RIV) or cell culture-based inactivated influenza vaccine (ccIIV) during the first season (year 1) were re-randomized the second season of 2019-2020 (year 2 [Y2]) to receive ccIIV or RIV, resulting in 4 ccIIV/RIV combinations. In Y2, hemagglutination inhibition antibody titers against reference cell-grown vaccine viruses were compared in each ccIIV/RIV group with titers among HCP randomized both seasons to receive egg-based, standard-dose inactivated influenza vaccine (IIV) using geometric mean titer (GMT) ratios of Y2 post-vaccination titers. RESULTS: Y2 data from 414 HCP were analyzed per protocol. Compared with 60 IIV/IIV recipients, 74 RIV/RIV and 106 ccIIV/RIV recipients showed significantly elevated GMT ratios (Bonferroni corrected P < .007) against all components except A(H3N2). Post-vaccination GMT ratios for ccIIV/ccIIV and RIV/ccIIV were not significantly elevated compared with IIV/IIV except for RIV/ccIIV against A(H1N1)pdm09. CONCLUSIONS: In adult HCP, receipt of RIV in 2 consecutive seasons or the second season was more immunogenic than consecutive egg-based IIV for 3 of the 4 components of quadrivalent vaccine. Immunogenicity of ccIIV/ccIIV was similar to that of IIV/IIV. Differences in HA antigen content may play a role in immunogenicity of influenza vaccination in consecutive seasons. CLINICAL TRIALS REGISTRATION: NCT03722589.

Leveraging International Influenza Surveillance Systems and Programs during the COVID-19 Pandemic.

A network of global respiratory disease surveillance systems and partnerships has been built over decades as a direct response to the persistent threat of seasonal, zoonotic, and pandemic influenza. These efforts have been spearheaded by the World Health Organization, country ministries of health, the US Centers for Disease Control and Prevention, nongovernmental organizations, academic groups, and others. During the COVID-19 pandemic, the US Centers for Disease Control and Prevention worked closely with ministries of health in partner countries and the World Health Organization to leverage influenza surveillance systems and programs to respond to SARS-CoV-2 transmission. Countries used existing surveillance systems for severe acute respiratory infection and influenza-like illness, respiratory virus laboratory resources, pandemic influenza preparedness plans, and ongoing population-based influenza studies to track, study, and respond to SARS-CoV-2 infections. The incorporation of COVID-19 surveillance into existing influenza sentinel surveillance systems can support continued global surveillance for respiratory viruses with pandemic potential.

Vital Signs: Influenza Hospitalizations and Vaccination Coverage by Race and Ethnicity-United States, 2009-10 Through 2021-22 Influenza Seasons.

Introduction: CDC estimates that influenza resulted in 9-41 million illnesses, 140,000-710,000 hospitalizations, and 12,000-52,000 deaths annually during 2010-2020. Persons from some racial and ethnic minority groups have historically experienced higher rates of severe influenza and had lower influenza vaccination coverage compared with non-Hispanic White (White) persons. This report examines influenza hospitalization and vaccination rates by race and ethnicity during a 12-13-year period (through the 2021-22 influenza season). Methods: Data from population-based surveillance for laboratory-confirmed influenza-associated hospitalizations in selected states participating in the Influenza-Associated Hospitalization Surveillance Network (FluSurv-NET) from the 2009-10 through 2021-22 influenza seasons (excluding 2020-21) and influenza vaccination coverage data from the Behavioral Risk Factor Surveillance System (BRFSS) from the 2010-11 through 2021-22 influenza seasons were analyzed by race and ethnicity. Results: From 2009-10 through 2021-22, age-adjusted influenza hospitalization rates (hospitalizations per 100,000 population) were higher among non-Hispanic Black (Black) (rate ratio [RR] = 1.8), American Indian or Alaska Native (AI/AN; RR = 1.3), and Hispanic (RR = 1.2) adults, compared with the rate among White adults. During the 2021-22 season, influenza vaccination coverage was lower among Hispanic (37.9%), AI/AN (40.9%), Black (42.0%), and other/multiple race (42.6%) adults compared with that among White (53.9%) and non-Hispanic Asian (Asian) (54.2%) adults; coverage has been consistently higher among White and Asian adults compared with that among Black and Hispanic adults since the 2010-11 season. The disparity in vaccination coverage by race and ethnicity was present among those who reported having medical insurance, a personal health care provider, and a routine medical checkup in the past year. Conclusions and Implications for Public Health Practice: Racial and ethnic disparities in influenza disease severity and influenza vaccination coverage persist. Health care providers should assess patient vaccination status at all medical visits and offer (or provide a referral for) all recommended vaccines. Tailored programmatic efforts to provide influenza vaccination through nontraditional settings, along with national and community-level efforts to improve awareness of the importance of influenza vaccination in preventing illness, hospitalization, and death among racial and ethnic minority communities might help address health care access barriers and improve vaccine confidence, leading to decreases in disparities in influenza vaccination coverage and disease severity.

Prevention and Control of Seasonal Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices - United States, 2022-23 Influenza Season.

THIS REPORT UPDATES THE 2021-22 RECOMMENDATIONS OF THE ADVISORY COMMITTEE ON IMMUNIZATION PRACTICES (ACIP) CONCERNING THE USE OF SEASONAL INFLUENZA VACCINES IN THE UNITED STATES: (MMWR Recomm Rep 2021;70[No. RR-5]:1-24). Routine annual influenza vaccination is recommended for all persons aged ≥6 months who do not have contraindications. For each recipient, a licensed and age-appropriate vaccine should be used. With the exception of vaccination for adults aged ≥65 years, ACIP makes no preferential recommendation for a specific vaccine when more than one licensed, recommended, and age-appropriate vaccine is available. All seasonal influenza vaccines expected to be available in the United States for the 2022-23 season are quadrivalent, containing hemagglutinin (HA) derived from one influenza A(H1N1)pdm09 virus, one influenza A(H3N2) virus, one influenza B/Victoria lineage virus, and one influenza B/Yamagata lineage virus. Inactivated influenza vaccines (IIV4s), recombinant influenza vaccine (RIV4), and live attenuated influenza vaccine (LAIV4) are expected to be available. Trivalent influenza vaccines are no longer available, but data that involve these vaccines are included for reference. INFLUENZA VACCINES MIGHT BE AVAILABLE AS EARLY AS JULY OR AUGUST, BUT FOR MOST PERSONS WHO NEED ONLY 1 DOSE OF INFLUENZA VACCINE FOR THE SEASON, VACCINATION SHOULD IDEALLY BE OFFERED DURING SEPTEMBER OR OCTOBER. HOWEVER, VACCINATION SHOULD CONTINUE AFTER OCTOBER AND THROUGHOUT THE SEASON AS LONG AS INFLUENZA VIRUSES ARE CIRCULATING AND UNEXPIRED VACCINE IS AVAILABLE. FOR MOST ADULTS (PARTICULARLY ADULTS AGED ≥65 YEARS) AND FOR PREGNANT PERSONS IN THE FIRST OR SECOND TRIMESTER, VACCINATION DURING JULY AND AUGUST SHOULD BE AVOIDED UNLESS THERE IS CONCERN THAT VACCINATION LATER IN THE SEASON MIGHT NOT BE POSSIBLE. CERTAIN CHILDREN AGED 6 MONTHS THROUGH 8 YEARS NEED 2 DOSES; THESE CHILDREN SHOULD RECEIVE THE FIRST DOSE AS SOON AS POSSIBLE AFTER VACCINE IS AVAILABLE, INCLUDING DURING JULY AND AUGUST. VACCINATION DURING JULY AND AUGUST CAN BE CONSIDERED FOR CHILDREN OF ANY AGE WHO NEED ONLY 1 DOSE FOR THE SEASON AND FOR PREGNANT PERSONS WHO ARE IN THE THIRD TRIMESTER IF VACCINE IS AVAILABLE DURING THOSE MONTHS: UPDATES DESCRIBED IN THIS REPORT REFLECT DISCUSSIONS DURING PUBLIC MEETINGS OF ACIP THAT WERE HELD ON OCTOBER 20, 2021; JANUARY 12, 2022; FEBRUARY 23, 2022; AND JUNE 22, 2022. PRIMARY UPDATES TO THIS REPORT INCLUDE THE FOLLOWING THREE TOPICS: 1) THE COMPOSITION OF 2022-23 U.S. SEASONAL INFLUENZA VACCINES; 2) UPDATES TO THE DESCRIPTION OF INFLUENZA VACCINES EXPECTED TO BE AVAILABLE FOR THE 2022-23 SEASON, INCLUDING ONE INFLUENZA VACCINE LABELING CHANGE THAT OCCURRED AFTER THE PUBLICATION OF THE 2021-22 ACIP INFLUENZA RECOMMENDATIONS; AND 3) UPDATES TO THE RECOMMENDATIONS CONCERNING VACCINATION OF ADULTS AGED ≥65 YEARS. FIRST, THE COMPOSITION OF 2022-23 U.S. INFLUENZA VACCINES INCLUDES UPDATES TO THE INFLUENZA A(H3N2) AND INFLUENZA B/VICTORIA LINEAGE COMPONENTS. U.S.-LICENSED INFLUENZA VACCINES WILL CONTAIN HA DERIVED FROM AN INFLUENZA A/VICTORIA/2570/2019 (H1N1)PDM09-LIKE VIRUS (FOR EGG-BASED VACCINES) OR AN INFLUENZA A/WISCONSIN/588/2019 (H1N1)PDM09-LIKE VIRUS (FOR CELL CULTURE-BASED OR RECOMBINANT VACCINES); AN INFLUENZA A/DARWIN/9/2021 (H3N2)-LIKE VIRUS (FOR EGG-BASED VACCINES) OR AN INFLUENZA A/DARWIN/6/2021 (H3N2)-LIKE VIRUS (FOR CELL CULTURE-BASED OR RECOMBINANT VACCINES); AN INFLUENZA B/AUSTRIA/1359417/2021 (VICTORIA LINEAGE)-LIKE VIRUS; AND AN INFLUENZA B/PHUKET/3073/2013 (YAMAGATA LINEAGE)-LIKE VIRUS. SECOND, THE APPROVED AGE INDICATION FOR THE CELL CULTURE-BASED INACTIVATED INFLUENZA VACCINE, FLUCELVAX QUADRIVALENT (CCIIV4), WAS CHANGED IN OCTOBER 2021 FROM ≥2 YEARS TO ≥6 MONTHS. THIRD, RECOMMENDATIONS FOR VACCINATION OF ADULTS AGED ≥65 YEARS HAVE BEEN MODIFIED. ACIP RECOMMENDS THAT ADULTS AGED ≥65 YEARS PREFERENTIALLY RECEIVE ANY ONE OF THE FOLLOWING HIGHER DOSE OR ADJUVANTED INFLUENZA VACCINES: QUADRIVALENT HIGH-DOSE INACTIVATED INFLUENZA VACCINE (HD-IIV4), QUADRIVALENT RECOMBINANT INFLUENZA VACCINE (RIV4), OR QUADRIVALENT ADJUVANTED INACTIVATED INFLUENZA VACCINE (AIIV4). IF NONE OF THESE THREE VACCINES IS AVAILABLE AT AN OPPORTUNITY FOR VACCINE ADMINISTRATION, THEN ANY OTHER AGE-APPROPRIATE INFLUENZA VACCINE SHOULD BE USED: THIS REPORT FOCUSES ON RECOMMENDATIONS FOR THE USE OF VACCINES FOR THE PREVENTION AND CONTROL OF SEASONAL INFLUENZA DURING THE 2022-23 INFLUENZA SEASON IN THE UNITED STATES. A BRIEF SUMMARY OF THE RECOMMENDATIONS AND A LINK TO THE MOST RECENT BACKGROUND DOCUMENT CONTAINING ADDITIONAL INFORMATION ARE AVAILABLE AT: https://www.cdc.gov/vaccines/hcp/acip-recs/vacc-specific/flu.html. These recommendations apply to U.S.-licensed influenza vaccines used according to Food and Drug Administration-licensed indications. Updates and other information are available from CDC's influenza website (https://www.cdc.gov/flu). Vaccination and health care providers should check this site periodically for additional information.

SARS-CoV-2 Convalescent Sera Binding and Neutralizing Antibody Concentrations Compared with COVID-19 Vaccine Efficacy Estimates against Symptomatic Infection.

Previous COVID-19 vaccine efficacy (VE) studies have estimated neutralizing and binding antibody concentrations that correlate with protection from symptomatic infection; how these estimates compare to those generated in response to SARS-CoV-2 infection is unclear. Here, we assessed quantitative neutralizing and binding antibody concentrations using standardized SARS-CoV-2 assays on 3,067 serum specimens collected during 27 July 2020 to 27 August 2020 from COVID-19-unvaccinated persons with detectable anti-SARS-CoV-2 antibodies. Neutralizing and binding antibody concentrations were severalfold lower in the unvaccinated study population compared to published concentrations at 28 days postvaccination. In this convenience sample, ~88% of neutralizing and ~63 to 86% of binding antibody concentrations met or exceeded concentrations associated with 70% COVID-19 VE against symptomatic infection; ~30% of neutralizing and 1 to 14% of binding antibody concentrations met or exceeded concentrations associated with 90% COVID-19 VE. Our study not only supports observations of infection-induced immunity and current recommendations for vaccination postinfection to maximize protection against COVID-19, but also provides a large data set of pre-COVID-19 vaccination anti-SARS-CoV-2 antibody concentrations that will serve as an important comparator in the current setting of vaccine-induced and hybrid immunity. As new SARS-CoV-2 variants emerge and displace circulating virus strains, we recommend that standardized binding antibody assays that include spike protein-based antigens be utilized to estimate antibody concentrations correlated with protection from COVID-19. These estimates will be helpful in informing public health guidance, such as the need for additional COVID-19 vaccine booster doses to prevent symptomatic infection. IMPORTANCE Although COVID-19 vaccine efficacy (VE) studies have estimated antibody concentrations that correlate with protection from COVID-19, how these estimates compare to those generated in response to SARS-CoV-2 infection is unclear. We assessed quantitative neutralizing and binding antibody concentrations using standardized assays on serum specimens collected from COVID-19-unvaccinated persons with detectable antibodies. We found that most unvaccinated persons with qualitative antibody evidence of prior infection had quantitative antibody concentrations that met or exceeded concentrations associated with 70% VE against COVID-19. However, only a small proportion had antibody concentrations that met or exceeded concentrations associated with 90% VE, suggesting that persons with prior COVID-19 would benefit from vaccination to maximize protective antibody concentrations against COVID-19.

Influenza Activity and Composition of the 2022-23 Influenza Vaccine - United States, 2021-22 Season.

Before the emergence of SARS-CoV-2, the virus that causes COVID-19, influenza activity in the United States typically began to increase in the fall and peaked in February. During the 2021-22 season, influenza activity began to increase in November and remained elevated until mid-June, featuring two distinct waves, with A(H3N2) viruses predominating for the entire season. This report summarizes influenza activity during October 3, 2021-June 11, 2022, in the United States and describes the composition of the Northern Hemisphere 2022-23 influenza vaccine. Although influenza activity is decreasing and circulation during summer is typically low, remaining vigilant for influenza infections, performing testing for seasonal influenza viruses, and monitoring for novel influenza A virus infections are important. An outbreak of highly pathogenic avian influenza A(H5N1) is ongoing; health care providers and persons with exposure to sick or infected birds should remain vigilant for onset of symptoms consistent with influenza. Receiving a seasonal influenza vaccine each year remains the best way to protect against seasonal influenza and its potentially severe consequences.

United States Centers for Disease Control and Prevention support for influenza surveillance, 2013-2021.

Objective: To assess the stability of improvements in global respiratory virus surveillance in countries supported by the United States Centers for Disease Control and Prevention (CDC) after reductions in CDC funding and with the stress of the coronavirus disease 2019 (COVID-19) pandemic. Methods: We assessed whether national influenza surveillance systems of CDC-funded countries: (i) continued to analyse as many specimens between 2013 and 2021; (ii) participated in activities of the World Health Organization's (WHO) Global Influenza Surveillance and Response System; (iii) tested enough specimens to detect rare events or signals of unusual activity; and (iv) demonstrated stability before and during the COVID-19 pandemic. We used CDC budget records and data from the WHO Global Influenza Surveillance and Response System. Findings: While CDC reduced per-country influenza funding by about 75% over 10 years, the number of specimens tested annually remained stable (mean 2261). Reporting varied substantially by country and transmission zone. Countries funded by CDC accounted for 71% (range 61-75%) of specimens included in WHO consultations on the composition of influenza virus vaccines. In 2019, only eight of the 17 transmission zones sent enough specimens to WHO collaborating centres before the vaccine composition meeting to reliably identify antigenic variants. Conclusion: Great progress has been made in the global understanding of influenza trends and seasonality. To optimize surveillance to identify atypical influenza viruses, and to integrate molecular testing, sequencing and reporting of severe acute respiratory syndrome coronavirus 2 into existing systems, funding must continue to support these efforts.

Interim Estimates of 2021-22 Seasonal Influenza Vaccine Effectiveness - United States, February 2022.

In the United States, annual vaccination against seasonal influenza is recommended for all persons aged ≥6 months except when contraindicated (1). Currently available influenza vaccines are designed to protect against four influenza viruses: A(H1N1)pdm09 (the 2009 pandemic virus), A(H3N2), B/Victoria lineage, and B/Yamagata lineage. Most influenza viruses detected this season have been A(H3N2) (2). With the exception of the 2020-21 season, when data were insufficient to generate an estimate, CDC has estimated the effectiveness of seasonal influenza vaccine at preventing laboratory-confirmed, mild/moderate (outpatient) medically attended acute respiratory infection (ARI) each season since 2004-05. This interim report uses data from 3,636 children and adults with ARI enrolled in the U.S. Influenza Vaccine Effectiveness Network during October 4, 2021-February 12, 2022. Overall, vaccine effectiveness (VE) against medically attended outpatient ARI associated with influenza A(H3N2) virus was 16% (95% CI = -16% to 39%), which is considered not statistically significant. This analysis indicates that influenza vaccination did not reduce the risk for outpatient medically attended illness with influenza A(H3N2) viruses that predominated so far this season. Enrollment was insufficient to generate reliable VE estimates by age group or by type of influenza vaccine product (1). CDC recommends influenza antiviral medications as an adjunct to vaccination; the potential public health benefit of antiviral medications is magnified in the context of reduced influenza VE. CDC routinely recommends that health care providers continue to administer influenza vaccine to persons aged ≥6 months as long as influenza viruses are circulating, even when VE against one virus is reduced, because vaccine can prevent serious outcomes (e.g., hospitalization, intensive care unit (ICU) admission, or death) that are associated with influenza A(H3N2) virus infection and might protect against other influenza viruses that could circulate later in the season.

Twelve-Month Follow-up of Early COVID-19 Cases in the United States: Cellular and Humoral Immune Longevity.

We quantify antibody and memory B-cell responses to severe acute respiratory syndrome coronavirus 2 at 6 and 12 months postinfection among 7 unvaccinated US coronavirus disease 2019 cases. All had detectable S-specific memory B cells and immunoglobulin G at both time points, with geometric mean titers of 117.2 BAU/mL and 84.0 BAU/mL at 6 and 12 months, respectively.

Severity of the COVID-19 pandemic assessed with all-cause mortality in the United States during 2020.

BACKGROUND: In the United States, infection with SARS-CoV-2 caused 380,000 reported deaths from March to December 2020. METHODS: We adapted the Moving Epidemic Method to all-cause mortality data from the United States to assess the severity of the COVID-19 pandemic across age groups and all 50 states. By comparing all-cause mortality during the pandemic with intensity thresholds derived from recent, historical all-cause mortality, we categorized each week from March to December 2020 as either low severity, moderate severity, high severity, or very high severity. RESULTS: Nationally for all ages combined, all-cause mortality was in the very high severity category for 9 weeks. Among people 18 to 49 years of age, there were 29 weeks of consecutive very high severity mortality. Forty-seven states, the District of Columbia, and New York City each experienced at least 1 week of very high severity mortality for all ages combined. CONCLUSIONS: These periods of very high severity of mortality during March through December 2020 are likely directly or indirectly attributable to the COVID-19 pandemic. This method for standardized comparison of severity over time across different geographies and demographic groups provides valuable information to understand the impact of the COVID-19 pandemic and to identify specific locations or subgroups for deeper investigations into differences in severity.

Laboratory-Confirmed COVID-19 Among Adults Hospitalized with COVID-19-Like Illness with Infection-Induced or mRNA Vaccine-Induced SARS-CoV-2 Immunity - Nine States, January-September 2021.

Previous infection with SARS-CoV-2 (the virus that causes COVID-19) or COVID-19 vaccination can provide immunity and protection from subsequent SARS-CoV-2 infection and illness. CDC used data from the VISION Network* to examine hospitalizations in adults with COVID-19-like illness and compared the odds of receiving a positive SARS-CoV-2 test result, and thus having laboratory-confirmed COVID-19, between unvaccinated patients with a previous SARS-CoV-2 infection occurring 90-179 days before COVID-19-like illness hospitalization, and patients who were fully vaccinated with an mRNA COVID-19 vaccine 90-179 days before hospitalization with no previous documented SARS-CoV-2 infection. Hospitalized adults aged ≥18 years with COVID-19-like illness were included if they had received testing at least twice: once associated with a COVID-19-like illness hospitalization during January-September 2021 and at least once earlier (since February 1, 2020, and ≥14 days before that hospitalization). Among COVID-19-like illness hospitalizations in persons whose previous infection or vaccination occurred 90-179 days earlier, the odds of laboratory-confirmed COVID-19 (adjusted for sociodemographic and health characteristics) among unvaccinated, previously infected adults were higher than the odds among fully vaccinated recipients of an mRNA COVID-19 vaccine with no previous documented infection (adjusted odds ratio [aOR] = 5.49; 95% confidence interval [CI] = 2.75-10.99). These findings suggest that among hospitalized adults with COVID-19-like illness whose previous infection or vaccination occurred 90-179 days earlier, vaccine-induced immunity was more protective than infection-induced immunity against laboratory-confirmed COVID-19. All eligible persons should be vaccinated against COVID-19 as soon as possible, including unvaccinated persons previously infected with SARS-CoV-2.

Effectiveness of 2-Dose Vaccination with mRNA COVID-19 Vaccines Against COVID-19-Associated Hospitalizations Among Immunocompromised Adults - Nine States, January-September 2021.

Immunocompromised persons, defined as those with suppressed humoral or cellular immunity resulting from health conditions or medications, account for approximately 3% of the U.S. adult population (1). Immunocompromised adults are at increased risk for severe COVID-19 outcomes (2) and might not acquire the same level of protection from COVID-19 mRNA vaccines as do immunocompetent adults (3,4). To evaluate vaccine effectiveness (VE) among immunocompromised adults, data from the VISION Network* on hospitalizations among persons aged ≥18 years with COVID-19-like illness from 187 hospitals in nine states during January 17-September 5, 2021 were analyzed. Using selected discharge diagnoses,† VE against COVID-19-associated hospitalization conferred by completing a 2-dose series of an mRNA COVID-19 vaccine ≥14 days before the index hospitalization date§ (i.e., being fully vaccinated) was evaluated using a test-negative design comparing 20,101 immunocompromised adults (10,564 [53%] of whom were fully vaccinated) and 69,116 immunocompetent adults (29,456 [43%] of whom were fully vaccinated). VE of 2 doses of mRNA COVID-19 vaccine against COVID-19-associated hospitalization was lower among immunocompromised patients (77%; 95% confidence interval [CI] = 74%-80%) than among immunocompetent patients (90%; 95% CI = 89%-91%). This difference persisted irrespective of mRNA vaccine product, age group, and timing of hospitalization relative to SARS-CoV-2 (the virus that causes COVID-19) B.1.617.2 (Delta) variant predominance in the state of hospitalization. VE varied across immunocompromising condition subgroups, ranging from 59% (organ or stem cell transplant recipients) to 81% (persons with a rheumatologic or inflammatory disorder). Immunocompromised persons benefit from mRNA COVID-19 vaccination but are less protected from severe COVID-19 outcomes than are immunocompetent persons, and VE varies among immunocompromised subgroups. Immunocompromised persons receiving mRNA COVID-19 vaccines should receive 3 doses and a booster, consistent with CDC recommendations (5), practice nonpharmaceutical interventions, and, if infected, be monitored closely and considered early for proven therapies that can prevent severe outcomes.

Performance of Self-Collected Anterior Nasal Swabs and Saliva Specimens for Detection of SARS-CoV-2 During Symptomatic and Asymptomatic Periods.

BACKGROUND: Anterior nasal swabs (ANS) are established specimen collection methods for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection detection. While saliva (SA) specimens provide an alternative, few studies have comprehensively characterized the performance of SA specimens in longitudinal studies. METHODS: We compared SARS-CoV-2 detections between paired self-collected ANS and SA specimens from a household transmission study. Participants recorded symptoms and paired ANS and SA specimens daily for 14 days. Specimens were tested using RT-PCR. We calculated the proportion of detections identified by each specimen type among the detections from both types combined. We computed percent agreement and Kappa statistics to assess concordance in detections. We also computed estimates stratified by presence of symptoms and examined the influence of traditional and inactivating transport media on the performance of ANS. RESULTS: We examined 2535 self-collected paired specimens from 216 participants. Among 1238 (49%) paired specimens with detections by either specimen type, ANS identified 77.1% (954; 95% CI, 74.6% to 79.3%) and SA 81.9% (1014; 95% CI, 79.7% to 84.0%), with a difference of 4.9% (95% CI, 1.4% to 8.5%). Overall agreement was 80.0%, and Kappa was 0.6 (95% CI, 0.5 to 0.6). Nevertheless, the difference in the proportion of detections identified by ANS and SA using traditional and inactivating transport media was 32.5% (95% CI, 26.8% to 38.0%) and -9.5% (95% CI, -13.7% to -5.2%), respectively. Among participants who remained asymptomatic, the difference in detections between SA and ANS was 51.2% (95% CI, 31.8% to 66.0%) and 26.1% (95% CI, 0% to 48.5%) using traditional and inactivating media, respectively. CONCLUSIONS: Self-collected saliva specimens provide a noninvasive alternative to nasal swabs, especially to those collected in traditional transport media, for longitudinal field studies that aim to detect both symptomatic and asymptomatic SARS-CoV-2 infections.