Evaluating COVID-19 vaccine effectiveness during pre-Delta, Delta and Omicron dominant periods among pregnant people in the U.S.: Retrospective cohort analysis from a nationally sampled cohort in National COVID Collaborative Cohort (N3C).

Objectives: To evaluate the effectiveness of COVID-19 vaccinations (initial and booster) during pre-Delta, Delta, and Omicron dominant periods among pregnant people via (1) COVID-19 incident and severe infections among pregnant people who were vaccinated vs. unvaccinated and (2) post-COVID-19 vaccination breakthrough infections and severe infections among vaccinated females who were pregnant vs. non-pregnant. Design: Retrospective cohort study using nationally sampled electronic health records data from the National COVID Cohort Collaborative (N3C), December 10, 2020, to June 07, 2022. Participants: Cohort 1 included pregnant people (15-55 years), and Cohort 2 included vaccinated females of reproductive age (15-55 years). Exposures: (1) COVID-19 vaccination and (2) pregnancy. Main outcome measures: Adjusted hazard ratios (aHRs) for COVID-19 incident or breakthrough infections and severe infections (i.e., COVID-19 infections with related hospitalizations). Results: In Cohort 1, 301,107 pregnant people were included. Compared to unvaccinated pregnant people, the aHRs for pregnant people with initial vaccinations during pregnancy of incident COVID-19 were 0.77 (95% CI: 0.62, 0.96) and 0.88 (95%CI: 0.73, 1.07) and aHRs of severe COVID-19 infections were 0.65 (95% CI: 0.47, 0.90) and 0.79 (95% CI: 0.51, 1.21) during the Delta and Omicron periods, respectively. Compared to pregnant people with full initial vaccinations, the aHR of incident COVID-19 for pregnant people with booster vaccinations was 0.64 (95% CI: 0.58, 0.71) during the Omicron period. In Cohort 2, 934,337 vaccinated people were included. Compared to vaccinated non-pregnant females, the aHRs of severe COVID-19 infections for people with initial vaccinations during pregnancy was 2.71 (95% CI: 1.31, 5.60) during the Omicron periods. Conclusions: Pregnant people with initial and booster vaccinations during pregnancy had a lower risk of incident and severe COVID-19 infections compared to unvaccinated pregnant people across the pandemic stages. However, vaccinated pregnant people still had a higher risk of severe infections compared to non-pregnant females.

Effectiveness of influenza vaccines in children aged 6 to 59 months: a test-negative case-control study at primary care and hospital level, Spain 2023/24.

During 2023/24, all children aged 6 to 59 months were targeted for seasonal influenza vaccination in Spain nationally. Using a test-negative case-control design with sentinel surveillance data, we estimated adjusted influenza vaccine effectiveness (IVE) against any influenza type to be 70% (95% confidence interval (CI): 51 to 81%) for primary care patients with acute respiratory illness (ARI) and 77% (95% CI: 21 to 93%) for hospitalised patients with severe ARI. In primary care, where most subtyped viruses (61%; 145/237) were A(H1N1), adjusted IVE was 77% (95% CI: 56 to 88%) against A(H1N1)pdm09.

Real-world effectiveness of influenza vaccine over a decade during the 2011-2021 seasons-Implications of vaccine mismatch.

BACKGROUND: Influenza imposes a significant healthcare burden in Korea, leading the government to initiate a national immunization program. Previous studies on vaccine effectiveness (VE) were limited to single-season estimation in Korea. METHODS: This multicenter prospective cohort study enrolled patients with influenza-like illnesses at 10 medical centers in Korea from 2011 to 2021. The demographic and clinical data were collected from questionnaire surveys and electronic medical records. Using a test-negative design, we aimed to investigate the effectiveness of a seasonal influenza vaccine for antigenic matching of the vaccine and circulating viral strains over 10 seasons. RESULTS: Overall, 5322 adults aged ≥65 years were enrolled. Only three (33.3 %) of nine seasons showed >70 % antigenic match between vaccine and circulating strains. Influenza VE was significantly variable by season, ranging from -46.9 % (95 %confidence interval [CI]: -127.6-5.2) in the 2011/12 season to 47.7 % (95 %CI: 22.6-64.7) in the 2016/17 season. A significant difference was observed in the VE depending on whether the vaccine strains matched with epidemic strains: 28.8 % (95 %CI: 8.8-44.8) in matched seasons versus -12.0 % (95 %CI: -30.0-3.7) in mismatched seasons. Across the study period, influenza-related hospitalizations were reduced by 13.6 % (95 %CI: 0.7-24.8) with vaccination. In a subgroup analysis, the VE against influenza-related hospitalization was 48.4 % (95 %CI 29.6-62.2) in A/H3N2 dominant seasons and 53.8 % (95 %CI: -73.4-87.7) in A/H1N1 dominant seasons, respectively. CONCLUSION: Influenza vaccine mismatch was frequent over the study period, leading to negligibly low VE in mismatched seasons. Influenza vaccination reduces the risk of influenza-related hospitalizations.

Relative effectiveness of COVID-19 vaccine booster doses in people aged 65 and older-a retrospective cohort study in Türkiye.

Background: Immunization in the elderly population is critical due to the high frequency of health outcomes related to COVID-19. Objectives: This study aimed to compare the effectiveness levels of COVID-19 vaccine schedules in preventing SARS-CoV-2 infection in the older adult group who received at least one booster dose. Design: Retrospective cohort study. Methods: This study evaluated 8969 adults aged 65 and over in the Sultanbeyli district of Istanbul. COVID-19 vaccination and SARS-CoV-2 polymerase chain reaction testing data between January 14, 2021 and December 2, 2022 were obtained from the National Public Health Management System. Results: The median age of participants was 71 years. The vaccines were mostly administered as CoronaVac for the first and second doses (81.4% and 82.2%, respectively) and BNT162b2 for the third and fourth doses (61.8% and 73.1%, respectively). Turkovac was administered only in booster doses (third dose 0.6%, fourth dose 4.8%). The adjusted relative vaccine effectiveness (rVE) was found to be 61.8% (95% confidence interval (CI) 51.5-69.9) in two doses of inactivated vaccine and one dose of mRNA vaccine schedule compared to the homolog booster of CoronaVac primary vaccine schedule. In two booster doses receipts, the adjusted rVE was found to be 45.4% (95% CI 13.8-65.4) in three doses of inactivated and one dose mRNA vaccine schedule and 43.0% (95% CI 20.5-59.2) in two doses of inactivated and two doses of mRNA vaccines schedule compared to the two homolog boosters with CoronaVac primary vaccine schedule. Conclusion: In this study, the effectiveness of the mRNA vaccine as a booster dose was higher than that of the homologous boosters in participants receiving the CoronaVac primary series for those aged 65 and over.

Mpox in People With Human Immunodeficiency Virus: Predictors of Diagnosis, Outcomes, and Vaccine Effectiveness in a Multisite Cohort.

INTRODUCTION: Since its global reemergence in 2022, monkeypox (mpox) has demonstrated increased incidence and severity among people with human immunodeficiency virus (HIV [PWH]). Predictors of mpox diagnosis, vaccination, and outcomes among PWH are limited. METHODS: We included PWH with primary care visits after 1 January 2022 at 9 US sites participating in the Centers for AIDS Research Network of Integrated Clinic Systems Network. We identified mpox diagnosed between 1 June 2022 and 31 May 2023, through a combination of polymerase chain reaction result, diagnosis code, and/or tecovirimat receipt. We examined validated clinical diagnoses, laboratory results, vaccine data, and patient reported outcomes. We evaluated relative risks (RR) of mpox diagnosis, hospitalization, tecovirimat treatment, and vaccine receipt. FINDINGS: Among 19 777 PWH in care, 413 mpox cases (all male sex at birth) occurred (2.2 cases/100 person-years). Age <40 years, geographic region, Hispanic/Latine ethnicity, lack of antiretroviral therapy, detectable HIV viral load, and recent bacterial sexually transmitted infection predicted mpox diagnosis. PWH with CD4 200-349 cells/mm3 were most likely to be hospitalized (adjusted RR, 3.20; 95% confidence interval: 1.44-7.09) compared to CD4 ≥500, but half as likely as those with CD4 <200 to receive tecovirimat. Overall, smallpox/mpox vaccine effectiveness of ≥1 vaccine was 71% (adjusted RR, 0.29; 95% confidence interval: .14-.47) at preventing mpox, and 86% or better with CD4 ≥350 or HIV viral suppression. Non-Hispanic Black PWH were less likely to be vaccinated than other racial/ethnic identities. INTERPRETATION: PWH not on antiretroviral therapy or with unsuppressed HIV were more likely to be diagnosed with, and hospitalized for, mpox. Mpox/smallpox vaccine effectiveness was high, inclusive of those with low CD4 count and HIV viremia.

Molecular epidemiology and vaccine compatibility analysis of seasonal influenza A viruses in the context of COVID-19 epidemic in Wuhan, China.

The COVID-19 pandemic had a significant impact on the global influenza vaccination and the epidemics of seasonal influenza. To further explore the molecular epidemiology of influenza viruses and assess vaccine effectiveness, we collected influenza cases in Wuhan during the 2022-2023 influenza season. Among 1312 clinical samples, 312 samples tested positive for influenza viruses using reverse transcription polymerase chain reaction. These positive samples included 146A/H1N1 subtypes (46.8%), 164A/H3N2 subtypes (52.6%) and 2 influenza B virus types (0.6%). Based on the whole genome sequence information of hemagglutinin (HA) and neuraminidase (NA) from 27A/H1N1 influenza virus strains and 26A/H3N2 influenza virus strains obtained in this study, a phylogenetic analysis was conducted. The analysis revealed that all A/H1N1 strains belonged to the evolutionary branch 6B.1A.5a.2a, and they exhibited specific substitutions at positions K71Q, Q206E, E241A, and R276K. Similarly, all A/H3N2 strains were classified into the 3C.2a1b.2a.1a subclade and displayed amino acid substitutions at positions S172H, N175Y, I176T, K187N, and S214P. Notably, the A/H3N2 strains also acquired a new potential glycosylation site at position N174. Using an epitope model, the predicted vaccine effectiveness was assessed for the A/H1N1 and A/H3N2 strains. The predicted vaccine effectiveness against the Wuhan influenza epidemic strain was over 85% for the A/H1N1 vaccine strain. However, the effectiveness against the A/H3N2 vaccine strain was only 48.7%. To further verify the protection of influenza vaccine against circulating influenza viruses in the region, we conducted in vivo and in vitro animal studies. The results of in vitro neutralization experiment showed that rabbit serum antibodies inoculated with quadrivalent isolated influenza vaccine had neutralization ability against all 24 isolated influenza viruses. In vivo experiments showed that vaccinated mice had fewer lung lesions when infected with the influenza strain circulating in Wuhan, suggesting that vaccination can effectively reduce the occurrence of severe lung damage. These findings emphasize the importance of accurately predicting seasonal influenza strains for effective influenza prevention and control, especially during the co-circulation of SARS-CoV-2 and influenza viruses. This study provides valuable information on the seasonal influenza virus in Wuhan during the COVID-19 pandemic and serves as a basis for vaccine prediction and updates.

Effectiveness of the Bivalent mRNA COVID-19 Vaccine for Preventing Critical Infection From the SARS-CoV-2 Omicron Variant in the Republic of Korea.

BACKGROUND: This retrospective observational matched cohort study assessed the differences in critical infections caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) during the omicron-predominant period of the coronavirus disease 2019 (COVID-19) pandemic. We evaluated the vaccine effectiveness of bivalent mRNA vaccine compared to unvaccinated individuals. METHODS: We collected COVID-19 case data from the Korean COVID-19 vaccine effectiveness cohort. We calculated the probability of critical COVID-19 cases by comparing the vaccinated and unvaccinated groups. RESULTS: The risk of being critically infected due to SAR-CoV-2 infection was 5.96 times higher (95% confidence interval, 5.63-6.38) among older individuals who were unvaccinated compared to those who received the bivalent COVID-19 vaccine. CONCLUSION: Our findings indicate that the bivalent vaccine reduces the disease burden of the SARS-CoV-2 omicron variant, particularly among the older population. Further studies are warranted to determine the effectiveness of booster doses of vaccines for SARS-CoV-2 infection.

Mpox Epidemiology and Vaccine Effectiveness, England, 2023.

Reported mpox cases in England continued at a low but steady frequency during 2023. Of 137 cases reported in 2023, approximately half were acquired overseas and half were in vaccinated persons. Estimated effectiveness of 2-dose vaccine was 80%, and no vaccinated mpox patient was hospitalized.

Effectiveness of a serogroup B meningococcal vaccine against gonorrhea: A retrospective study.

BACKGROUND: Outer membrane vesicle (OMV) meningococcal serogroup B (MenB) vaccines might be protective against gonorrhea. We evaluated the effectiveness of MenB-4C, an OMV MenB vaccine, against gonorrhea. METHODS: We identified gonococcal mono-infections, chlamydial mono-infections, and gonococcal/chlamydial co-infections among persons aged 15-30 years in the electronic health records of Kaiser Permanente Northern California during 2016-2021. We determined MenB-4C vaccination status (vaccinated [≥1 MenB-4C vaccine dose] or unvaccinated [MenB-4C vaccine naïve]) at each infection. We used log-binomial regression with generalized estimating equations to calculate adjusted prevalence ratios (APR) and 95 % confidence intervals (CI) to determine if MenB-4C vaccination was protective against gonococcal mono-infections compared to chlamydial mono-infection. We also evaluated if MenB-4C vaccination was protective against gonococcal/chlamydial co-infections. Because of concerns with small sample size of vaccinated persons, we estimated effects using a limited model (adjusting for race/ethnicity only) and an expanded model (adjusting for additional potential confounders). RESULTS: Of 68,454 persons, we identified 558 (0.8 %) MenB-4C vaccinated persons and 85,393 infections (13,000 gonococcal mono-infections, 68,008 chlamydial mono-infections, and 4385 gonococcal/chlamydial co-infections). After adjusting for race/ethnicity, MenB-4C vaccination was 23 % protective against gonococcal mono-infection compared to chlamydial mono-infection (APR = 0.77, 95 % CI = 0.64-0.99) in the limited model but not in the expanded model. CONCLUSION: MenB-4C vaccination was protective against gonococcal mono-infection, independent of race/ethnicity. This protective effect was not observed when other potential confounders were included in the analysis. Protection against gonococcal/chlamydial co-infection was not observed. Efficacy data from clinical trials are needed.

Monovalent rotavirus vaccine effectiveness and long-term impact among children <5 years old in Antananarivo, Madagascar, 2010-2022.

BACKGROUND: Monovalent rotavirus vaccine substantially reduced rotavirus disease burden after introduction (May 2014) in Madagascar. We examined the effectiveness and long-term impact on acute watery diarrhea and rotavirus-related hospitalizations among children <5 years old at two hospitals in Antananarivo, Madagascar (2010-2022). METHODS: We used a test-negative case-control design to estimate monovalent rotavirus vaccine effectiveness (VE) against laboratory-confirmed rotavirus hospitalizations among children age 6-23 months with documented vaccination status adjusted for year of symptom onset, rotavirus season, age group, nutritional status, and clinical severity. To evaluate the impact, we expanded to children age 0-59 months with acute watery diarrhea. First, we used admission logbook data to compare the proportion of all hospitalizations attributed to diarrhea in the pre-vaccine (January 2010-December 2013), transition period (January 2014-December 2014), and post-vaccine (January 2015-December 2022) periods. Second, we used active surveillance data (June 2013-May 2022) to describe rotavirus positivity and detected genotypes by vaccine introduction period and surveillance year (1 June-31 May). RESULT: Adjusted VE of at least one dose against hospitalization due to rotavirus diarrhea among children age 6-23 months was 61 % (95 % CI: -39 %-89 %). The annual median proportion of hospitalizations attributed to diarrhea declined from 28 % in the pre-vaccine to 10 % in the post-vaccine period. Rotavirus positivity among hospitalized children age 0-59 months with acute watery diarrhea was substantially higher during the pre-vaccine (59 %) than the post-vaccine (23 %) period. In the pre-vaccine period, G3P[8] (76 %) and G2P[4] (12 %) were the dominant genotypes detected. Although genotypes varied by surveillance year, G1P[8] and G2P[4] represented >50 % of the genotypes detected post-introduction. CONCLUSIONS: Rotavirus vaccine has been successfully implemented in Madagascar's routine childhood immunization program and had a large impact on rotavirus disease burden, supporting continued use of rotavirus vaccines in Madagascar.

Relative effectiveness of bivalent boosters against severe COVID-19 outcomes among people aged ≥ 65 years in Finland, September 2022 to August 2023.

BackgroundLong-term effectiveness data on bivalent COVID-19 boosters are limited.AimWe evaluated the long-term protection of bivalent boosters against severe COVID-19 among ≥ 65-year-olds in Finland.MethodsIn this register-based cohort analysis, we compared the risk of three severe COVID-19 outcomes among ≥ 65-year-olds who received a bivalent booster (Original/Omicron BA.1 or Original/BA.4-5; exposed group) between 1/9/2022 and 31/8/2023 to those who did not (unexposed). We included individuals vaccinated with at least two monovalent COVID-19 vaccine doses before 1/9/2022 and ≥ 3 months ago. The analysis was divided into two periods: 1/9/2022-28/2/2023 (BA.5 and BQ.1.X predominating) and 1/3/2023-31/8/2023 (XBB predominating). The hazards for the outcomes between exposed and unexposed individuals were compared with Cox regression.ResultsWe included 1,191,871 individuals. From 1/9/2022 to 28/2/2023, bivalent boosters were associated with a reduced risk of hospitalisation due to COVID-19 (hazard ratio (HR): 0.45; 95% confidence interval (CI): 0.37-0.55), death due to COVID-19 (HR: 0.49; 95% CI: 0.38-0.62), and death in which COVID-19 was a contributing factor (HR: 0.40; 95% CI: 0.31-0.51) during 14-60 days since vaccination. From 1/3/2023 to 31/8/2023, bivalent boosters were associated with lower risks of all three severe COVID-19 outcomes during 61-120 days since a bivalent booster (e.g. HR: 0.53; 95% CI: 0.39-0.71 for hospitalisation due to COVID-19); thereafter no notable risk reduction was observed. No difference was found between Original/Omicron BA.1 and Original/BA.4-5 boosters.ConclusionBivalent boosters initially reduced the risk of severe COVID-19 outcomes by ca 50% among ≥ 65-year-olds, but protection waned over time. These findings help guide vaccine development and vaccination programmes.

Elevated body mass index is not significantly associated with reduced influenza vaccine effectiveness.

Elevated body mass index (BMI) has been linked to severe influenza illness and impaired vaccine immunogenicity, but the relationship between BMI and clinical vaccine effectiveness (VE) is less well described. This secondary analysis of data from a test-negative study of outpatients with acute respiratory illness assessed BMI and VE against medically attended, PCR-confirmed influenza over seven seasons (2011-12 through 2017-18). Vaccination status was determined from electronic medical records (EMR) and self-report; BMI was estimated from EMR-documented height and weight categorized for adults as obesity (≥ 30 kg/m2), overweight (25-29 kg/m2), or normal and for children based on standardized z-scales. Current season VE by virus type/subtype was estimated separately for adults and children. Pooled VE for all seasons was calculated as 1-adjusted odds ratios from logistic regression with an interaction term for BMI and vaccination. Among 28,089 adults and 12,380 children, BMI category was not significantly associated with VE against outpatient influenza for any type/subtype. Adjusted VE against A/H3N2, A/H1N1pdm09, and B in adults ranged from 16-31, 46-54, and 44-57%, and in children from 29-34, 57-65, and 50-55%, respectively, across the BMI categories. Elevated BMI was not associated with reduced VE against laboratory confirmed, outpatient influenza illness.

Health impact of rotavirus vaccination in China.

Rotavirus (RV) vaccines have demonstrated substantial effectiveness in reducing the healthcare burden caused by gastroenteritis (RVGE) worldwide. This study aims to understand the differential impact of RV vaccination in reducing RVGE burden in children under 7 years old in China. A Markov Model was used to investigate the health impact of introducing two different RV vaccines into the Chinese population. The analysis was conducted for RV5, a live pentavalent human-bovine reassortant vaccine, and Lanzhou Lamb RV (LLR), a live-attenuated monovalent RV vaccine, separately, by comparing the strategy of each vaccine to no vaccination within a Chinese birth cohort, including 100,000 children modeled until 7 years of age. The vaccination scenario assumed a vaccination coverage of 2.5%, 2.5%, 90% and 5% for doses one, two, three and no vaccine, respectively, for both vaccines. Strategies with RV5, LLR, and no vaccination were associated with 9,895, 49,069, and 64,746 symptomatic RV infections, respectively. RV5 and LLR were associated with an 85% and 24% reduction in the total symptomatic RV infections, respectively, suggesting that the health benefits of RV5 are at least three-fold greater than those associated with the LLR. Further, strategies with RV5 and LLR resulted in an estimated 206 and 59-year increase in quality-adjusted life years (QALYs), respectively. Sensitivity and scenario analyses supported the robustness of the base-case findings. Use of RV vaccine is expected to improve RV-associated health outcomes and its adoption will help alleviate the burden of RVGE in China. RV5 use will result in significantly better health outcomes.

COVID-19 breakthrough infections in vaccinated individuals at BPKIHS, Nepal.

BACKGROUND: Although there have been reports of COVID-19 breakthrough infections in vaccinated individuals, the vaccines have demonstrated a high efficacy in preventing severe illness and death. Nepal has reported fewer studies of COVID-19 breakthrough infections. Hence, this study has objective to assess the prevalence, and to describe clinical characteristics of severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) breakthrough infection. METHODS: This descriptive study was conducted from January to December 2022. The study enrolled 200 individuals who had received the recommended doses of the COVID-19 vaccine and they were RT-PCR positive diagnosed with vaccine breakthrough infections after 14 days of completing the vaccination course. The patient's demographic and clinical profiles, as well as their outcomes in terms of severity, length of hospital stay, and mortality were recorded. RESULTS: The prevalence of SARS-CoV2 infection was 6.3% (547/8682). Among fully vaccinated personnel, the prevalence of breakthrough infections was 6.2% (200/3175). This study found the Omicron variants in respondents. The mean age of the patients was 38.28 years, and 41.5% (83/200) of the breakthrough cases were healthcare workers. The mean time gap between the second dose of vaccination and a positive RT-PCR test was 354.68 days. Of the 200 breakthrough cases, 89% (178) had mild symptoms, 9% (17) had moderate symptoms requiring hospitalization, and 2% (4) were severe cases that required intensive care facility. Among the severe cases, 3 out 4 were above 60 years old. Furthermore, the patients greater than 60 years had longer hospital stays (p < 0.0001) however no deaths were recorded. CONCLUSION: Fully vaccinated individuals can experience COVID-19 breakthrough infections and the majority of cases present with mild symptoms. Elderly patients have a higher likelihood of severe disease and longer hospital stay compared to younger patients. The results of this study emphasize the importance of vaccination in mitigating the severity of the disease.

Effectiveness of inactivated COVID-19 vaccines in preventing COVID-19-related hospitalization during the Omicron BF.7-predominant epidemic wave in Beijing, China: a cohort study.

BACKGROUND: To estimate vaccine effectiveness(VE) against COVID-19-related hospitalization for inactivated vaccines during the Omicron BF.7-predominant epidemic wave in Beijing, China. METHODS: We recruited a cohort in Beijing on 17 and 18 December 2022, collected status of vaccination and COVID-19-related hospitalization since 1 November 2022 and prospectively followed until 9 January 2023. A Poisson regression model was used to estimate the VE. RESULTS: 16(1.15%) COVID-19-related hospitalizations were reported in 1391 unvaccinated participants; 7(0.25%) in 2765 participants with two doses, resulting in a VE of 70.89%(95% confidence interval[CI] 26.25 to 87.73); 32(0.27%) in 11,846 participants with three doses, with a VE of 65.25%(95% CI 32.24 to 81.83). The VE of three doses remained above 64% at 1 year or more since the last dose. Elderly people aged ≥ 60 years had the highest hospitalization incidence(0.66%), VE for two doses was 74.11%(95%CI: - 18.42 to 94.34) and VE for three doses was 80.98%(95%CI:52.83 to 92.33). We estimated that vaccination had averted 65,007(95%CI: 12,817 to 97,757) COVID-19-related hospitalizations among people aged ≥ 60 years during the BF.7-predominant period in Beijing. CONCLUSION: Inactivated COVID-19 vaccines were effective against COVID-19-related hospitalization, especially for the elderly population who have increased risk of severe disease owing to SARS-CoV-2 infection.

Comparative effectiveness of bivalent BA.4-5 or BA.1 mRNA booster vaccines among immunocompromised individuals across three Nordic countries: A nationwide cohort study.

OBJECTIVES: To estimate the effectiveness and waning of the bivalent BA.4-5 or BA.1 mRNA booster vaccine against Covid-19-related hospitalization and death in immunocompromised individuals. METHODS: Nationwide analyses across Nordic countries from 1 September 2022 to 31 October 2023 using a matched cohort design. Individuals boosted with a BA.4-5 or BA.1 vaccine were matched 1:1 with unboosted individuals. The outcomes of interest were country-combined vaccine effectiveness (VE) estimates against Covid-19-related hospitalization and death at day 270 of follow-up. Waning was assessed in 45-day intervals. RESULTS: A total of 352,762 BA.4-5 and 191,070 BA.1 booster vaccine doses were included. At day 270, the comparative VE against Covid-19-related hospitalization was 34.2% (95% CI, 7.1% to 61.3%) for the bivalent BA.4-5 vaccine and 42.6% (95% CI, 31.3% to 53.9%) for the BA.1 vaccine compared with matched unboosted. The comparative VE against Covid-19-related death was 53.9% (95% CI, 38.6% to 69.3%) for the bivalent BA.4-5 vaccine and 57.9% (95% CI, 48.5% to 67.4%) for the BA.1 vaccine. CONCLUSIONS: In immunocompromised individuals, vaccination with bivalent BA.4-5 or BA.1 booster lowered the risk of Covid-19-related hospitalization and death over a follow-up period of 9 months. The effectiveness was highest during the first months since vaccination with subsequent gradual waning.

Evaluation of the COVID-19 vaccine effectiveness on the outcomes of COVID 19 disease in Iran: a test-negative case-control study.

Introduction: This study measures the COVID-19 vaccine effectiveness (CVE) against hospital admission and severe COVID-19. Methods: This study is a test-negative case-control design using data from eight provinces in April, 2021 until March, 2022. The individuals were classified as cases and controls based on the results of the RT-PCR test for SARS-CoV-2 and matched based on the timing of the test being conducted as well as the timing of hospital admission. The measure of association was an odds ratio (OR) by univariate and multiple logistic regression. The multiple logistic regression has been carried out to take confounding factors and potential effect modifiers into account. The CVE was computed as CVE = (1 - OR)*100 with 95% confidence interval. Results: Among 19314 admitted patients, of whom 13216 (68.4%) were cases and 6098 (31.6%) were controls, 1313 (6.8%) died. From total, 5959 (30.8%) patients had received the vaccine in which one, two, and booster doses were 2443 (12.6%), 2796 (14.5Ùª), and 720 (3.7Ùª), respectively. The estimated adjusted effectiveness of only one dose, two doses and booter vaccination were 22% (95% CI: 14%-29%), 35% (95% CI: 29%-41%) and 33% (95% CI: 16%-47%), respectively. In addition, the adjusted vaccine effectiveness against severe outcome was 33% (95% CI: 19%- 44%), 34% (95% CI: 20%- 45%) and 20% (95% CI: -29%- 50%) for those who received one, two and booster vaccinations, respectively. Conclusion: Our study concluded that full vaccination, though less effective compared to similar studies elsewhere, decreased hospital admissions and deaths from COVID-19 in Iran, particularly during the Delta variant period, with an observed decline during the Omicron variant dominance.

Evaluating the impact of extended dosing intervals on mRNA COVID-19 vaccine effectiveness in adolescents.

BACKGROUND: Extending the dosing interval of a primary series of mRNA COVID-19 vaccination has been employed to reduce myocarditis risk in adolescents, but previous evaluation of impact on vaccine effectiveness (VE) is limited to risk after second dose. METHODS: We quantified the impact of the dosing interval based on case notifications and vaccination uptake in Hong Kong from January to April 2022, based on calendar-time proportional hazards models and matching approaches. RESULTS: We estimated that the hazard ratio (HR) and odds ratio (OR) of infections after the second dose for extended (28 days or more) versus regular (21-27 days) dosing intervals ranged from 0.86 to 0.99 from calendar-time proportional hazards models, and from 0.85 to 0.87 from matching approaches, respectively. Adolescents in the extended dosing groups (including those who did not receive a second dose in the study period) had a higher hazard of infection than those with a regular dosing interval during the intra-dose period (HR 1.66; 95% CI 1.07, 2.59; p = 0.02) after the first dose. CONCLUSIONS: Implementing an extended dosing interval should consider multiple factors including the degree of myocarditis risk, the degree of protection afforded by each dose, and the extra protection achievable using an extended dosing interval.

Wastewater-Based Surveillance Reveals the Effectiveness of the First COVID-19 Vaccination Campaigns in Assisted Living Facilities.

The COVID-19 pandemic has disproportionately affected vulnerable populations, including residents of assisted living facilities (ALFs). This study investigates the impact of non-pharmaceutical interventions (NPIs) and mass vaccination campaigns on SARS-CoV-2 transmission dynamics within four ALFs in Maricopa County, Arizona, United States from January to April 2021. Initial observations reveal a significant SARS-CoV-2 prevalence in Maricopa County, with 7452 new COVID-19 cases reported on 4 January 2021. Wastewater surveillance indicates elevated viral loads within ALFs with peak concentrations reaching 1.35 × 107 genome copies/L at Facility 1 and 4.68 × 105 copies/L at Facility 2. The implementation of NPIs, including isolation protocols, resulted in a rapid decline in viral loads in wastewater. Following mass vaccination campaigns, viral loads reduced across all facilities, except Facility 4. Facility 1 demonstrated a mean viral load decrease from 1.65 × 106 copies/L to 1.04 × 103 copies/L post-vaccination, with a statistically significant U-statistic of 28.0 (p-value = 0.0027). Similar trends are observed in Facilities 2 and 3, albeit with varying degrees of statistical significance. In conclusion, this study provides evidence supporting the role of NPIs and vaccination campaigns in controlling SARS-CoV-2 transmission within ALFs.

Indirect effectiveness of COVID-19 vaccines in the pre-omicron and omicron periods: A nation-wide test-negative case-control study in Brazil.

OBJECTIVES: Mass COVID-19 immunization campaigns altered the pandemic's progress by protecting the vaccine recipient and reducing transmission. However, evidence for indirect vaccine effectiveness (IVE) is limited due to the difficulties of ascertaining this type of protection. METHODS: Using linked national Brazilian databases, we adapted the test-negative design to evaluate the IVE against symptomatic infection. We analyzed data from January 1 to December 1, 2021 (pre-omicron) and January 1 to April 30, 2022 (omicron BA.1 and BA.2). We compared the probability of testing positive across various levels of second ancestral-strain monovalent COVID-19 vaccine dose coverage, including only unvaccinated individuals in the main analysis and both vaccinated and unvaccinated individuals in additional analyses. Sensitivity analysis focused on children younger than 12 years who did not have access to COVID-19 vaccines during the pre-omicron period. RESULTS: We included 11,039,315 unvaccinated individuals tested during the pre-omicron study period. IVE was minimal until 30% vaccination coverage (<10%), then it followed a dose-dependent pattern, peaking at 37.7 (95% confidence interval 32-42.8) at 70% coverage. For children younger than 12 years, IVE peaked at 59.8% (95% confidence interval 52.7-65.9) at 70% coverage. During the omicron period, IVE remained constant at about 5% across all comparisons. CONCLUSIONS: Our findings confirm that high vaccination coverage using vaccines that prevent infection indirectly protects the community. However, IVE was substantially higher during the pre-omicron period.