Use of the Pfizer Pentavalent Meningococcal Vaccine Among Persons Aged ≥10 Years: Recommendations of the Advisory Committee on Immunization Practices - United States, 2023.

Meningococcal disease is a life-threatening invasive infection caused by Neisseria meningitidis. Two quadrivalent (serogroups A, C, W, and Y) meningococcal conjugate vaccines (MenACWY) (MenACWY-CRM [Menveo, GSK] and MenACWY-TT [MenQuadfi, Sanofi Pasteur]) and two serogroup B meningococcal vaccines (MenB) (MenB-4C [Bexsero, GSK] and MenB-FHbp [Trumenba, Pfizer Inc.]), are licensed and available in the United States and have been recommended by CDC's Advisory Committee on Immunization Practices (ACIP). On October 20, 2023, the Food and Drug Administration approved the use of a pentavalent meningococcal vaccine (MenACWY-TT/MenB-FHbp [Penbraya, Pfizer Inc.]) for prevention of invasive disease caused by N. meningitidis serogroups A, B, C, W, and Y among persons aged 10-25 years. On October 25, 2023, ACIP recommended that MenACWY-TT/MenB-FHbp may be used when both MenACWY and MenB are indicated at the same visit for the following groups: 1) healthy persons aged 16-23 years (routine schedule) when shared clinical decision-making favors administration of MenB vaccine, and 2) persons aged ≥10 years who are at increased risk for meningococcal disease (e.g., because of persistent complement deficiencies, complement inhibitor use, or functional or anatomic asplenia). Different manufacturers' serogroup B-containing vaccines are not interchangeable; therefore, when MenACWY-TT/MenB-FHbp is used, subsequent doses of MenB should be from the same manufacturer (Pfizer Inc.). This report summarizes evidence considered for these recommendations and provides clinical guidance for the use of MenACWY-TT/MenB-FHbp.

Tick-Borne Encephalitis Vaccine: Recommendations of the Advisory Committee on Immunization Practices, United States, 2023.

Tick-borne encephalitis (TBE) virus is focally endemic in parts of Europe and Asia. The virus is primarily transmitted to humans by the bites of infected: Ixodes species ticks but can also be acquired less frequently by alimentary transmission. Other rare modes of transmission include through breastfeeding, blood transfusion, solid organ transplantation, and slaughtering of viremic animals. TBE virus can cause acute neurologic disease, which usually results in hospitalization, often permanent neurologic or cognitive sequelae, and sometimes death. TBE virus infection is a risk for certain travelers and for laboratory workers who work with the virus. In August 2021, the Food and Drug Administration approved Ticovac TBE vaccine for use among persons aged ≥1 year. This report summarizes the epidemiology of and risks for infection with TBE virus, provides information on the immunogenicity and safety of TBE vaccine, and summarizes the recommendations of the Advisory Committee on Immunization Practices (ACIP) for use of TBE vaccine among U.S. travelers and laboratory workers.

Pneumococcal Vaccine for Adults Aged ≥19 Years: Recommendations of the Advisory Committee on Immunization Practices, United States, 2023

his report compiles and summarizes all published recommendations from CDC's Advisory Committee on Immunization Practices (ACIP) for use of pneumococcal vaccines in adults aged ≥19 years in the United States. This report also includes updated and new clinical guidance for implementation from CDC. Before 2021, ACIP recommended 23-valent pneumococcal polysaccharide vaccine (PPSV23) alone (up to 2 doses), or both a single dose of 13-valent pneumococcal conjugate vaccine (PCV13) in combination with 1­3 doses of PPSV23 in series (PCV13 followed by PPSV23), for use in U.S. adults depending on age and underlying risk for pneumococcal disease. In 2021, two new pneumococcal conjugate vaccines (PCVs), a 15-valent and a 20-valent PCV (PCV15 and PCV20), were licensed for use in U.S. adults aged ≥18 years by the Food and Drug Administration. ACIP recommendations specify the use of either PCV20 alone or PCV15 in series with PPSV23 for all adults aged ≥65 years and for adults aged 19­64 years with certain underlying medical conditions or other risk factors who have not received a PCV or whose vaccination history is unknown. In addition, ACIP recommends use of either a single dose of PCV20 or ≥1 dose of PPSV23 for adults who have started their pneumococcal vaccine series with PCV13 but have not received all recommended PPSV23 doses. Shared clinical decision-making is recommended regarding use of a supplemental PCV20 dose for adults aged ≥65 years who have completed their recommended vaccine series with both PCV13 and PPSV23. Updated and new clinical guidance for implementation from CDC includes the recommendation for use of PCV15 or PCV20 for adults who have received PPSV23 but have not received any PCV dose. The report also includes clinical guidance for adults who have received 7-valent PCV (PCV7) only and adults who are hematopoietic stem cell transplant recipients.

The Present and Future of the Adult Pneumococcal Vaccine Program in the United States.

Adult Pneumococcal Vaccine Program in the United StatesStreptococcus pneumoniae (pneumococcus) is a common cause of bacterial respiratory infections leading to substantial morbidity and mortality. Here, Kobayashi et al. discuss the recently updated U.S. guidelines for adult pneumococcal vaccination.

Use of 15-Valent Pneumococcal Conjugate Vaccine Among U.S. Children: Updated Recommendations of the Advisory Committee on Immunization Practices - United States, 2022.

The 13-valent pneumococcal conjugate vaccine (PCV13 [Prevnar 13, Wyeth Pharmaceuticals, Inc, a subsidiary of Pfizer, Inc]) and the 23-valent pneumococcal polysaccharide vaccine (PPSV23 [Merck Sharp & Dohme LLC]) have been recommended for U.S. children, and the recommendations vary by age group and risk group (1,2). In 2021, 15-valent pneumococcal conjugate vaccine (PCV15 [Vaxneuvance, Merck Sharp & Dohme LLC]) was licensed for use in adults aged ≥18 years (3). On June 17, 2022, the Food and Drug Administration (FDA) approved an expanded usage for PCV15 to include persons aged 6 weeks-17 years, based on studies that compared antibody responses to PCV15 with those to PCV13 (4). PCV15 contains serotypes 22F and 33F (in addition to the PCV13 serotypes) conjugated to CRM197 (genetically detoxified diphtheria toxin). On June 22, 2022, CDC's Advisory Committee on Immunization Practices (ACIP) recommended use of PCV15 as an option for pneumococcal conjugate vaccination of persons aged <19 years according to currently recommended PCV13 dosing and schedules (1,2). ACIP employed the Evidence to Recommendation (EtR) Framework,* using the Grading of Recommendations, Assessment, Development and Evaluation (GRADE)† approach to guide its deliberations regarding use of these vaccines. Risk-based recommendations on use of PPSV23 for persons aged 2-18 years with certain underlying medical conditions§ that increase the risk for pneumococcal disease have not changed.

Associations Between Weight and Lower Respiratory Tract Disease Outcomes in Hospitalized Children.

OBJECTIVE: To identify associations between weight status and clinical outcomes in children with lower respiratory tract infection (LRTI) or asthma requiring hospitalization. METHODS: We performed a retrospective cohort study of 2 to 17 year old children hospitalized for LRTI and/or asthma from 2009 to 2019 using electronic health record data from the PEDSnet clinical research network. Children <2 years, those with medical complexity, and those without a calculable BMI were excluded. Children were classified as having underweight, normal weight, overweight, or class 1, 2, or 3 obesity based on Body Mass Index percentile for age and sex. Primary outcomes were need for positive pressure respiratory support and ICU admission. Subgroup analyses were performed for children with a primary diagnosis of asthma. Outcomes were modeled with mixed-effects multivariable logistic regression incorporating age, sex, and payer as fixed effects. RESULTS: We identified 65 132 hospitalizations; 6.7% with underweight, 57.8% normal weight, 14.6% overweight, 13.2% class 1 obesity, 5.0% class 2 obesity, and 2.8% class 3 obesity. Overweight and obesity were associated with positive pressure respiratory support (class 3 obesity versus normal weight odds ratio [OR] 1.62 [1.38-1.89]) and ICU admission (class 3 obesity versus normal weight OR 1.26 [1.12-1.42]), with significant associations for all categories of overweight and obesity. Underweight was also associated with positive pressure respiratory support (OR 1.39 [1.24-1.56]) and ICU admission (1.40 [1.30-1.52]). CONCLUSIONS: Both underweight and overweight or obesity are associated with increased severity of LRTI or asthma in hospitalized children.

Dengue: A Growing Problem With New Interventions.

Dengue is the disease caused by 1 of 4 distinct, but closely related dengue viruses (DENV-1-4) that are transmitted by Aedes spp. mosquito vectors. It is the most common arboviral disease worldwide, with the greatest burden in tropical and sub-tropical regions. In the absence of effective prevention and control measures, dengue is projected to increase in both disease burden and geographic range. Given its increasing importance as an etiology of fever in the returning traveler or the possibility of local transmission in regions in the United States with competent vectors, as well as the risk for large outbreaks in endemic US territories and associated states, clinicians should understand its clinical presentation and be familiar with appropriate testing, triage, and management of patients with dengue. Control and prevention efforts reached a milestone in June 2021 when the Advisory Committee on Immunization Practices (ACIP) recommended Dengvaxia for routine use in children aged 9 to 16 years living in endemic areas with laboratory confirmation of previous dengue virus infection. Dengvaxia is the first vaccine against dengue to be recommended for use in the United States and one of the first to require laboratory testing of potential recipients to be eligible for vaccination. In this review, we outline dengue pathogenesis, epidemiology, and key clinical features for front-line clinicians evaluating patients presenting with dengue. We also provide a summary of Dengvaxia efficacy, safety, and considerations for use as well as an overview of other potential new tools to control and prevent the growing threat of dengue .

Use of 15-Valent Pneumococcal Conjugate Vaccine and 20-Valent Pneumococcal Conjugate Vaccine Among U.S. Adults: Updated Recommendations of the Advisory Committee on Immunization Practices - United States, 2022.

In 2021, 20-valent pneumococcal conjugate vaccine (PCV) (PCV20) (Wyeth Pharmaceuticals LLC, a subsidiary of Pfizer Inc.) and 15-valent PCV (PCV15) (Merck Sharp & Dohme Corp.) were licensed by the Food and Drug Administration for adults aged ≥18 years, based on studies that compared antibody responses to PCV20 and PCV15 with those to 13-valent PCV (PCV13) (Wyeth Pharmaceuticals LLC, a subsidiary of Pfizer Inc.). Antibody responses to two additional serotypes included in PCV15 were compared to corresponding responses after PCV13 vaccination, and antibody responses to seven additional serotypes included in PCV20 were compared with those to the 23-valent pneumococcal polysaccharide vaccine (PPSV23) (Merck Sharp & Dohme Corp.). On October 20, 2021, the Advisory Committee on Immunization Practices (ACIP) recommended use of either PCV20 alone or PCV15 in series with PPSV23 for all adults aged ≥65 years, and for adults aged 19-64 years with certain underlying medical conditions or other risk factors* who have not previously received a PCV or whose previous vaccination history is unknown. ACIP employed the Evidence to Recommendation (EtR) framework,† using the Grading of Recommendations, Assessment, Development and Evaluation (GRADE)§ approach to guide its deliberations regarding use of these vaccines. Before this, PCV13 and PPSV23 were recommended for use for U.S. adults and the recommendations varied by age and risk groups. This was simplified in the new recommendations.

Weight Status and Risk of Inpatient Admission for Children With Lower Respiratory Tract Disease.

OBJECTIVES: To identify associations between weight category and hospital admission for lower respiratory tract disease (LRTD), defined as asthma, community-acquired pneumonia, viral pneumonia, or bronchiolitis, among children evaluated in pediatric emergency departments (PEDs). METHODS: We performed a retrospective cohort study of children 2 to <18 years of age evaluated in the PED at 6 children's hospitals within the PEDSnet clinical research network from 2009 to 2019. BMI percentile of children was classified as underweight, healthy weight, overweight, and class 1, 2, or 3 obesity. Children with complex chronic conditions were excluded. Mixed-effects multivariable logistic regression was used to assess associations between BMI categories and hospitalization or 7- and 30-day PED revisits, adjusted for covariates (age, sex, race and ethnicity, and payer). RESULTS: Among 107 446 children with 218 180 PED evaluations for LRTD, 4.5% had underweight, 56.4% had healthy normal weight, 16.1% had overweight, 14.6% had class 1 obesity, 5.5% had class 2 obesity, and 3.0% had class 3 obesity. Underweight was associated with increased risk of hospital admission compared with normal weight (odds ratio [OR] 1.76; 95% confidence interval [CI] 1.69-1.84). Overweight (OR 0.87; 95% CI 0.85-0.90), class 1 obesity (OR 0.88; 95% CI 0.85-0.91), and class 2 obesity (OR 0.91; 95% CI 0.87-0.96) had negative associations with hospital admission. Class 1 and class 2, but not class 3, obesity had small positive associations with 7- and 30-day PED revisits. CONCLUSIONS: We found an inverse relationship between patient weight category and risk for hospital admission in children evaluated in the PED for LRTD.

Dengue Vaccine: Recommendations of the Advisory Committee on Immunization Practices, United States, 2021.

Dengue is a vectorborne infectious disease caused by dengue viruses (DENVs), which are predominantly transmitted by Aedes aegypti and Aedes albopictus mosquitos. Dengue is caused by four closely related viruses (DENV-1-4), and a person can be infected with each serotype for a total of four infections during their lifetime. Areas where dengue is endemic in the United States and its territories and freely associated states include Puerto Rico, American Samoa, the U.S. Virgin Islands, the Federated States of Micronesia, the Republic of Marshall Islands, and the Republic of Palau. This report summarizes the recommendations of the Advisory Committee on Immunization Practices (ACIP) for use of the Dengvaxia vaccine in the United States. The vaccine is a live-attenuated, chimeric tetravalent dengue vaccine built on a yellow fever 17D backbone. Dengvaxia is safe and effective in reducing dengue-related hospitalizations and severe dengue among persons who have had dengue infection in the past. Previous natural infection is important because Dengvaxia is associated with an increased risk for severe dengue in those who experience their first natural infection (i.e., primary infection) after vaccination. Dengvaxia was licensed by the Food and Drug Administration for use among children and adolescents aged 9-16 years (referred to in this report as children). ACIP recommends vaccination with Dengvaxia for children aged 9-16 having evidence of a previous dengue infection and living in areas where dengue is endemic. Evidence of previous dengue infection, such as detection of anti-DENV immunoglobulin G with a highly specific serodiagnostic test, will be required for eligible children before vaccination.

Suboptimal uptake of human papillomavirus (HPV) vaccine in survivors of childhood and adolescent and young adult (AYA) cancer.

PURPOSE: To estimate the population-based incidence of HPV vaccination after childhood cancer. METHODS: Pediatric and young adult cancer survivors identified in the institutional Comprehensive Cancer Center registry were linked to the North Carolina Immunization Registry (NCIR). Initiation and completion of any HPV vaccine was evaluated in survivors born between 1984 and 2002 with an NCIR record by December 2014. Descriptive statistics and Kaplan-Meier estimates of cumulative incidence were stratified by sex and age at eligibility for vaccine. Cox proportional hazards were conducted and stratified by sex. RESULTS: Among 879 (n = 428 female; n = 451 male) study-eligible cancer survivors without prior HPV vaccination (n = 501 < 18 years, n = 378 ≥ 18 years at the time of eligibility), the cumulative incidence of HPV vaccine initiation following cancer therapy was 48.1% among females at 8.2 years and 29.2% among males at 5.0 years after vaccine eligibility among those < 18 years, and 6.2% among females at 8.1 years and 2.0% among males at 4.2 years after vaccine eligibility among those ≥ 18 years. Among those who initiated vaccination, 53% of females and 43% of males completed a 3-dose series. Younger age at cancer diagnosis (≤ 10 and 11-14 years vs. ≥ 15 years) and shorter interval from diagnosis to vaccine eligibility were more likely to initiate vaccination in models adjusted for age at eligibility, race/ethnicity, cancer type, relapse, and transplant. CONCLUSIONS: Despite the benefit of a cancer prevention strategy, cancer survivors are sub-optimally vaccinated against HPV. IMPLICATIONS FOR CANCER SURVIVORS: Immunization registries can help oncologists and primary care providers identify gaps in vaccination and target HPV vaccine delivery in survivors.

Is weight associated with severity of acute respiratory illness?

BACKGROUND/OBJECTIVES: Obesity was an independent risk factor for severe disease in hospitalized adults during the 2009 pandemic H1N1 influenza season. Few studies have investigated the association between weight and severity of acute respiratory illnesses in children or in adults seeking care in the emergency department (ED) during other winter respiratory seasons. SUBJECTS/METHODS: We prospectively and systematically enrolled patients ≥2 years of age who presented to the ED or inpatient setting in a single geographic region with fever/acute respiratory illness over four consecutive winter respiratory seasons (2010-2014). We collected demography, height and weight, and high risk co-morbid conditions. Multivariable logistic regression was used for prediction of hospital admission (primary outcome), length of stay and supplemental oxygen requirement among those hospitalized, and antibiotic prescription (secondary outcomes). RESULTS: We enrolled 3560 patients (N = 749 children, 2811 adults), 1405 (39%) with normal weight, 860 (24%) with overweight, and 1295 (36%) with obesity. Following multivariable logistic regression, very young or very old age (p < 0.001) and high-risk conditions (p < 0.001) predicted hospitalization. Risk of hospitalization was decreased for adults with overweight [aOR 0.8 (95% CI 0.6-1.0)], class 1 obesity [aOR 0.7 (95% CI 0.5-1.0)], and class 2 obesity [aOR 0.6 (95% CI 0.4-0.8)] compared to normal-weight. Class 3 obesity was associated with supplemental oxygen requirement in adults [aOR 1.6 (95% CI 1.1-2.5)]. No association was seen in children. CONCLUSION: Overweight and obesity were not associated with increased risk of hospitalization during winter respiratory seasons in children or adults.

2015-2016 Vaccine Effectiveness of Live Attenuated and Inactivated Influenza Vaccines in Children in the United States.

Background: In the 2015-2016 season, quadrivalent live attenuated influenza vaccine (LAIV) and both trivalent and quadrivalent inactivated influenza vaccine (IIV) were available in the United States. Methods: This study, conducted according to a test-negative case-control design, enrolled children aged 2-17 years presenting to outpatient settings with fever and respiratory symptoms for <5 days at 8 sites across the United States between 30 November 2015 and 15 April 2016. A nasal swab was obtained for reverse-transcriptase polymerase chain reaction (RT-PCR) testing for influenza, and influenza vaccination was verified in the medical record or vaccine registry. Influenza vaccine effectiveness (VE) was estimated using a logistic regression model. Results: Of 1012 children retained for analysis, most children (59%) were unvaccinated, 10% received LAIV, and 31% received IIV. Influenza A (predominantly antigenically similar to the A/California/7/2009 strain) was detected in 14% and influenza B (predominantly a B/Victoria lineage) in 10%. For all influenza, VE was 46% (95% confidence interval [CI], 7%-69%) for LAIV and 65% (48%-76%) for IIV. VE against influenza A(H1N1)pdm09 was 50% (95% CI, -2% to 75%) for LAIV and 71% (51%-82%) for IIV. The odds ratio for vaccine failure with RT-PCR-confirmed A(H1N1)pdm09 was 1.71 (95% CI, 0.78-3.73) in LAIV versus IIV recipients. Conclusions: LAIV and IIV demonstrated effectiveness against any influenza among children aged 2-17 years in 2015-2016. When compared to all unvaccinated children, VE against influenza A(H1N1)pdm09 was significant for IIV but not LAIV. Clinical Trials Registration: NCT01997450.

Association of Prior Vaccination With Influenza Vaccine Effectiveness in Children Receiving Live Attenuated or Inactivated Vaccine.

Importance: Some studies have reported negative effects of prior-season influenza vaccination. Prior-season influenza vaccination effects on vaccine effectiveness (VE) in children are not well understood. Objective: To assess the association of prior-season influenza vaccination with subsequent VE in children aged 2 to 17 years. Design, Setting, and Participants: This multiseason, test-negative case-control study was conducted in outpatient clinics at 4 US sites among children aged 2 to 17 years with a medically attended febrile acute respiratory illness. Participants were recruited during the 2013-2014, 2014-2015, and 2015-2016 seasons when influenza circulated locally. Cases were children with influenza confirmed by reverse-transcription polymerase chain reaction. Test-negative control individuals were children with negative test results for influenza. Exposures: Vaccination history, including influenza vaccine type received in the enrollment season (live attenuated influenza vaccine [LAIV], inactivated influenza vaccine [IIV], or no vaccine) and season before enrollment (LAIV, IIV, or no vaccine), determined from medical records and immunization registries. Main Outcomes and Measures: LAIV and IIV effectiveness by influenza type and subtype (influenza A[H1N1]pdm09, influenza A[H3N2], or influenza B), estimated as 100 × (1 - odds ratio) in a logistic regression model with adjustment for potential confounders. Prior season vaccination associations were assessed with an interaction term. Results: Of 3369 children (1749 [52%] male; median age, 6.6 years [range, 2-17 years]) included in the analysis, 772 (23%) had a positive test result for influenza and 1674 (50%) were vaccinated in the enrollment season. Among LAIV recipients, VE against influenza A(H3N2) was higher among children vaccinated in both the enrollment and 1 prior season (50.3% [95% CI, 17.0% to 70.2%]) than among those without 1 prior season vaccination (-82.4% [95% CI, -267.5% to 9.5%], interaction P < .001). The effectiveness of LAIV against influenza A(H1N1)pdm09 was not associated with prior season vaccination among those with prior season vaccination (47.5% [95% CI, 11.4% to 68.9%]) and among those without prior season vaccination (7.8% [95% CI, -101.9% to 57.9%]) (interaction P = .37). Prior season vaccination was not associated with effectiveness of IIV against influenza A(H3N2) (38.7% [95% CI, 6.8% to 59.6%] among those with prior-season vaccination and 23.2% [95% CI, -38.3% to 57.4%] among those without prior-season vaccination, interaction P = .16) or with effectiveness of IIV against influenza A[H1N1]pdm09 (72.4% [95% CI, 56.0% to 82.7%] among those with prior season vaccination and 67.5% [95% CI, 32.1% to 84.4%] among those without prior season vaccination, interaction P = .93). Residual protection from prior season vaccination only (no vaccination in the enrollment season) was observed for influenza B (LAIV: 60.0% [95% CI, 36.8% to 74.7%]; IIV: 60.0% [36.9% to 74.6%]). Similar results were observed in analyses that included repeated vaccination in 2 and 3 prior seasons. Conclusions and Relevance: Influenza VE varied by influenza type and subtype and vaccine type, but prior-season vaccination was not associated with reduced VE. These findings support current recommendations for annual influenza vaccination of children.

Effectiveness of live attenuated influenza vaccine and inactivated influenza vaccine in children during the 2014-2015 season.

BACKGROUND: A clinical study found that live attenuated influenza vaccine (LAIV) was superior to inactivated influenza vaccine (IIV) against drifted A(H3N2) viruses in children. During the 2014-2015 influenza season, widespread circulation of antigenically and genetically drifted A(H3N2) viruses provided an opportunity to evaluate subtype-specific vaccine effectiveness (VE) of quadrivalent LAIV (LAIV4) and IIV in children. METHODS: Children (2-17years) with febrile acute respiratory illness <5days' duration were enrolled at 4 outpatient sites in the United States during the 2014-2015 influenza season. Nasal swabs were tested for influenza by reverse transcription polymerase chain reaction; vaccination dates were obtained from medical records or immunization registries. VE was estimated using a test-negative design comparing odds of vaccination among influenza cases and test-negative controls with adjustment for potential confounders. RESULTS: Among 1696 children enrolled, 1511 (89%) were included in the analysis. Influenza was detected in 427 (28%) children; 317 had influenza A(H3N2) and 110 had influenza B. Most influenza isolates were characterized as a drifted strain of influenza A(H3N2) or a drifted strain of B/Yamagata. For LAIV4, adjusted VE was 50% (95% confidence interval [CI], 27-66%) against any influenza, 30% (95% CI, -6% to 54%) against influenza A(H3N2), and 87% (95% CI, 63-96%) against type B. For IIV, adjusted VE was 39% (95% CI, 18-54%) against any influenza, 40% (95% CI, 16-58%) against A(H3N2), and 29% (95% CI, -15% to 56%) against type B. Odds of influenza for LAIV4 versus IIV recipients were similar against influenza A(H3N2) (odds ratio [OR], 1.17; 95% CI, 0.73-1.86) and lower against influenza B (OR, 0.18; 95% CI, 0.06-0.55). CONCLUSIONS: LAIV4 and IIV provided similar protection against a new antigenic variant A(H3N2). LAIV4 provided significantly greater protection than IIV against a drifted influenza B strain. ClinicalTrials.gov identifier: NCT01997450.

Estimating the Burden of Pandemic Infectious Disease: The Case of the Second Wave of Pandemic Influenza H1N1 in Forsyth County, North Carolina.

BACKGROUND: Understanding the burden of influenza A(H1N1)pdm09 virus during the second wave of 2009-2010 is important for future pandemic planning. METHODS: Persons who presented to the emergency department (ED) or were hospitalized with fever and/or acute respiratory symptoms at the academic medical center in Forsyth County, North Carolina were prospectively enrolled and underwent nasal/throat swab testing for influenza A(H1N1)pdm09. Laboratory-confirmed cases of influenza A(H1N1)pdm09 virus identified through active surveillance were compared by capture-recapture analysis to those identified through independent, passive surveillance (physician-ordered influenza testing). This approach estimated the number of total cases, including those not captured by either surveillance method. A second analysis estimated the total number of influenza A(H1N1)pdm09 cases by multiplying weekly influenza percentages determined via active surveillance by weekly counts of influenza-associated discharge diagnoses from administrative data. Market share adjustments were used to estimate influenza A(H1N1)pdm09 virus ED visits or hospitalizations per 1,000 residents. RESULTS: Capture-recapture analysis estimated that 753 residents (95% confidence interval [CI], 424-2,735) with influenza A(H1N1)pdm09 virus were seen in the academic medical center from September 2009 through mid-April 2010; this result yielded an estimated 4.7 (95% CI, 2.6-16.9) influenza A(H1N1)pdm09 virus ED visits or hospitalizations per 1,000 residents. Similarly, 708 visits were estimated using weekly influenza percentages and influenza-associated discharge diagnoses, yielding an estimated 4.4 influenza A(H1N1)pdm09 virus ED visits or hospitalizations per 1,000 residents. CONCLUSION: This study demonstrates that the burden of influenza A(H1N1)pdm09 virus in ED and inpatient settings by capture-recapture analysis was 4-5 per 1,000 residents; this rate was approximately 8-fold higher than that detected by physician-ordered influenza testing.