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.

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 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.

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.

Relative Effectiveness and Waning of a Third Dose of mRNA COVID-19 Vaccine in Medicare Beneficiaries Aged 65 Years and Older during the BA.1/BA.2 Omicron Period.

BACKGROUND: We assessed the added benefit and waning effectiveness of a third COVID-19 vaccine dose (original formula) for preventing COVID-19-related outcomes. METHODS: We used Medicare claims data to conduct a retrospective cohort study in U.S. community-dwelling Medicare Fee-for-Service beneficiaries aged ≥65 years during the BA.1/BA.2 Omicron period (December 19, 2021 - March 26, 2022). We estimated relative vaccine effectiveness (RVE) of 3 versus 2 doses of mRNA COVID-19 vaccines using marginal structural Cox regression models. RESULTS: Among 8,135,020 eligible beneficiaries, 73.3% were 3-dose vaccinated by March 26, 2022. At 14-60 days since vaccination, a third dose provided significant added benefit against COVID-19-related hospitalization for Moderna (RVE: 77.2%; 95% confidence interval (CI): 76.0%, 78.4%) and Pfizer-BioNTech (RVE: 72.5%; 95% CI: 70.8%, 74.0%). Added benefit was lower >120 days. For those with prior medically attended COVID-19 diagnoses, Pfizer-BioNTech provided an added benefit for 120 days, while Moderna provided some added benefit >120 days. Added benefit for either vaccine was higher against death compared to less severe outcomes, which still decreased >120 days. CONCLUSIONS: A third dose COVID-19 vaccine provided significant added benefit against COVID-19-related hospitalization and death, even for beneficiaries with prior medically attended COVID-19 diagnoses. This added benefit decreased after 4 months.

Effectiveness of bivalent HPV vaccination against genital HPV DNA-positivity of a catch-up campaign at age 13-16 years compared to routine vaccination at age 12 years: a biennial repeated cross-sectional study.

BACKGROUND: The Netherlands is one of few countries worldwide which has used the bivalent HPV vaccine for girls-only for over a decade. This allows assessment of vaccine effectiveness (VE) against female genital HPV DNA-positivity of this vaccine in an observational post-licencing real-world setting. Additionally, it is unclear whether catch-up vaccination campaigns result in similar VE as routine vaccination. Therefore, type-specific and grouped VE were assessed and compared for women who had been eligible for catch-up vaccination at 13-16 years with those who had been eligible for routine vaccination at 12 years. METHODS: PASSYON is a Dutch biennial repeated cross-sectional (2011-2021) study among sexual health clinic clients aged 16-24 years old. Women provided self-collected vaginal samples, questionnaires on demographics and sexual behaviour were administered, and women self-reported HPV vaccination status. Samples were analysed using a PCR-based assay (SPF10-LiPA25). Type-specific and grouped VE estimates, adjusted with propensity score stratification, were assessed against genital positivity for 14 HPV types. VE for targeted and non-targeted genotypes were compared between women who had been eligible for the catch-up and those who had been eligible for routine vaccination. RESULTS: The study included 4488 female participants who had been eligible for HPV vaccination and provided genital swabs (1561 eligible for catch-up, 2927 for routine vaccination). Very high VE against genital HPV-16 and HPV-18 was observed (resp. 93.5% and 89.5%) and significant cross-protection against six other genotypes (HPV-31/33/35/45/52/58), varying from 18.0% (HPV-52) to 79.6% (HPV-45). VE estimates were comparable between women who had been eligible for the catch-up campaign and those eligible for routine vaccination: VE HPV-16/HPV-18: 92.2% (95%CI: 87.9-94.9) vs. 91.8% (95%CI: 86.0-95.2). CONCLUSIONS: In real-world settings, the VE of bivalent vaccine is high against targeted genotypes, with cross-protection against 6 other genotypes. Catch-up campaigns up to age 16 years can be as effective as routine vaccination at age 12, although it is recommendable to provide HPV vaccination at an age at which most are likely not sexually active yet. This may inform countries considering catch-up campaigns when introducing or extending the use of HPV vaccination within their national immunisation programmes.

Modeling the population-level impact of a third dose of MMR vaccine on a mumps outbreak at the University of Iowa.

Mumps outbreaks among fully vaccinated young adults have raised questions about potential waning of immunity over time and need for a third dose of the measles, mumps, rubella (MMR) vaccine. However, there are currently limited data on real-life effectiveness of the third-dose MMR vaccine in preventing mumps. Here, we used a deterministic compartmental model to infer the effectiveness of the third-dose MMR vaccine in preventing mumps cases by analyzing the mumps outbreak that occurred at the University of Iowa between August 24, 2015, and May 13, 2016. The modeling approach further allowed us to evaluate the population-level impact of vaccination by different timing in relation to the start of the outbreak and varied coverage levels, and to account for potential sources of bias in estimating vaccine effectiveness. We found large uncertainty in vaccine effectiveness estimates; however, our models showed that early introduction of a third dose of MMR vaccine during a mumps outbreak can be effective in preventing transmission. School holidays, such as the winter break, likely played important roles in preventing mumps transmission.

Improved Methods for Vaccine Effectiveness Studies.

Evaluating the impact of public health investments in vaccination programs is crucial for ensuring their efficiency and effectiveness. Vaccine effectiveness (VE) studies, such as those using the test-negative design (TND), are commonly used to confirm the impact of vaccines and to guide future improvements. The TND, favored for its simplicity and cost efficiency, mitigates biases common in other epidemiological study designs. However, its validity can be compromised by inconsistent symptom definitions and retrospective data application. Here we summarize recent findings that highlight the need to address correlated vaccination behaviors when estimating VE, that suggest using negative control variables to reduce confounding, and that recommend accounting for prior infection history in VE studies to improve accuracy and reliability. These insights are important for refining VE estimation methods.

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.

A population database analysis to estimate the varicella vaccine effectiveness in children < 14 years in a high vaccination coverage area from 2004 to 2022.

INTRODUCTION: In the Veneto Region of Italy, universal varicella vaccination (VV) started in 2007 with a two-dose schedule at 12-15 months and 5-6 years of age achieving 90 % coverage in 2019. The study aimed at evaluating the vaccine effectiveness (VE) in children using a primary-care database METHODS: This retrospective analysis used Pedianet, a comprehensive database of 73 family paediatricians in the Veneto Region. Incidence rates (IR) of varicella were evaluated in children aged <14 years enrolled since birth, between January 2004 to April 2022. Cases were classified as breakthrough if happening beyond 42 days post-VV. Complications and prescription were evaluated. Subject were followed up from 2004 or the enrollment date, until the end of assistance/study or the first or second VV dose. Kaplan-Meier curves and log-rank tests were used to compare the varicella incidence by vaccination status. Hazard ratios of varicella infection, adjusted (aHRs) for sex, vaccinal status, age group, prematurity and socioeconomic status were estimated with Cox's regression. VE for one and two VV doses was defined as 1-aHR*. RESULTS: 36,498 children, followed for 233,508 person-years from 2004 to 2022 experienced 1006 cases of varicella (13 complicated and 35 breakthrough). Younger children had a higher risk of experiencing varicella compared to children aged >7 years, irrespective of their vaccination status. Indeed, the IR increased from 5.5 to 19.5 × 1000 person-years and from 1.1 to 5.4 × 1000 person-years in unvaccinated and vaccinated children aged <12 months versus those aged 5-6 years, respectively. Varicella VE was 83.4 % and 94.7 % in those vaccinated with one and two doses. After six years, the cumulative probability of experiencing varicella was 10.7 % for unvaccinated subjects, and 2.5 % and 0.4 % for those vaccinated with one and two-doses (log-rank test, p < 0.001). CONCLUSIONS: Two-dose schedule VV is effective in drastically reduce varicella episodes. Breakthrough varicella episodes remain rare events.

Effectiveness of the ten- and thirteen-valent pneumococcal conjugate vaccines to prevent serotype 19A invasive pneumococcal disease in Quebec, Canada. A Canadian immunization research network (CIRN) study.

In the province of Quebec, Canada, a 2 + 1 dose pneumococcal conjugate vaccine (PCV) program for children was implemented in 2004. PCV7, PCV10, PCV13 and a mixed PCV10/PCV13 schedule were sequentially used without catch-up. The effectiveness of vaccination schedules to prevent serotype 19A invasive pneumococcal disease (IPD) in <5-year-old children was estimated by the indirect cohort method during 2009-2023. A total of 248 19A IPD cases and 457 IPD controls were included in the analysis. Adjusted vaccine effectiveness (VEa) for ≥1 dose was 57 % [95 %CI: -1 %,82 %] for PCV10 and 62 % [16 %,83 %] for PCV13. VEa for 3 doses was 69 % [17 %,88 %] for PCV10, 76 % [39 %,90 %] for PCV13 and 86 % [64 %,95 %] for the 2PCV10 + 1PCV13 schedule. Protection provided by the PCV10-only schedule tended to be of lower magnitude compared to the two other schedules. The mixed PCV10 + PCV13 schedule showed a protection against 19A IPD at least comparable to that of 3 PCV-13 doses.

The impact of the implementation of the two-dose varicella vaccine immunization strategy in Quzhou: A retrospective birth cohort study.

Varicella is a vaccine-preventable disease caused by the varicella zoster virus (VZV), but the varicella incidence among children has increased in recent years. This was a retrospective birth cohort study based on the Zhejiang Provincial Immune Information System (ZJIIS) and the China Information System for Disease Control and Prevention (CISDCP) in Quzhou. A total of 1,291 clinically diagnosed varicella cases born from 2009 to 2014 were collected during 2009-2023, which were analyzed the impact of changes in vaccination strategy on the incidence of varicella based on the Cox-proportional hazards model. It was observed that the onset age of varicella shifted to the older age group and later to 9-11 years. After the change to the two-dose varicella vaccination strategy, the population affected by varicella was concentrated among students and received more than one dose of live attenuated varicella vaccine (VarV). Based on the Coxproportional hazards model and adjusting for all covariates, the risk of varicella infection in children decreased after the introduction of the two-dose varicella vaccination strategy (HR = 0.04, 95% CI: 0.03-0.05). Meanwhile, the Kaplan-Meier curves also showed that the hazards were lower after the change in vaccination strategy. It is recommended that two doses of VarV should be included in the national immunization schedule and that full vaccination should be completed approximately four years after the first dose.

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.

Estimates of vaccine effectiveness of the updated monovalent XBB.1.5 COVID-19 vaccine against symptomatic SARS-CoV-2 infection, hospitalization, and receipt of oxygen therapy in South Korea - October 26 to December 31, 2023.

OBJECTIVES: We evaluated the vaccine effectiveness of monovalent XBB.1.5 vaccine against symptomatic COVID-19 infection, hospitalization, and the need for oxygen therapy in South Korea. DESIGN: This study employed a test-negative case-control design. COVID-19 test results in symptomatic subjects from six university hospitals across South Korea were collected (October 26-December 31, 2023). The adjusted absolute and relative vaccine effectiveness were assessed. RESULTS: In total, 5516 subjects were enrolled: 4,824 were unvaccinated with XBB.1.5, and 692 were vaccinated with XBB.1.5 COVID-19 mRNA vaccines. The absolute vaccine effectiveness when comparing the odds between XBB.1.5 vaccination and no vaccination against symptomatic COVID-19 infection, hospitalization, and oxygen therapy was 65.2% (95% CI, 36.1-81.0), 77.3% (95% CI, 51.1-89.5), and 85.3% (95% CI, 57.8-94.9), respectively. The relative vaccine effectiveness when comparing the odds between XBB.1.5 vaccination and no XBB.1.5 vaccination against symptomatic COVID-19 infection, hospitalization, and oxygen therapy was 57.7% (95% CI, 34.7-72.6), 64.3% (95% CI, 35.9-80.2), and 65.5% (95% CI, 27.0-83.7), respectively. CONCLUSION: The short-term effectiveness of the XBB.1.5 vaccine against symptomatic COVID-19 infection, hospitalization, and receipt of oxygen therapy in South Korea was significant. Long-term vaccine effectiveness warrants evaluation, and these assessments should be conducted regularly.

Varicella vaccine effectiveness evaluation in Wuxi, China: A retrospective cohort study.

Varicella is a vaccine-preventable infectious disease. Since 1 December 2018, the varicella vaccine has been included in the local Expanded Programme on Immunization (EPI) in Wuxi, China, and children born after 1 December 2014 are eligible for free vaccination. To evaluate the effect of varicella vaccination in Wuxi city, we selected 382 397 children born from 2012 to 2016 as subjects. Their disease data were obtained from the Chinese Disease Prevention and Control Information System, and their vaccination data were obtained from the Jiangsu Province Vaccination Integrated Service Management Information System. The incidence of breakthrough varicella cases increased in the first 4 years and reached the peak in the fifth year. With the increase of vaccination rate, the incidence of varicella decreased significantly. The vaccine effectiveness (VE) was found to be 88.17%-95.78% for one dose and 98.65%-99.93% for two doses. Although the VE per dose decreased from 99.57% in the first year to 93.04% in the eighth year, it remained high. These findings confirmed the effectiveness of varicella vaccination in children, supported the use of a two-dose varicella vaccination strategy to achieve better protection, and provided important insights into the optimal vaccination strategy for varicella prevention in children.

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.

Protection of vaccine boosters and prior infection against mild/asymptomatic and moderate COVID-19 infection in the UK SIREN healthcare worker cohort: October 2023 to March 2024.

OBJECTIVES: Bivalent original/BA.4-5 and monovalent XBB.1.5 mRNA boosters were offered to UK healthcare workers (HCWs) in the autumn of 2023. We aimed to estimate booster vaccine effectiveness (VE) and post-infection immunity among the SIREN HCW cohort over the subsequent 6-month period of XBB.1.5 and JN.1 variant circulation. METHODS: Between October 2023 to March 2024, 2867 SIREN study participants tested fortnightly for SARS-CoV-2 and completed symptoms questionnaires. We used multi-state models, adjusted for vaccination, prior infection, and demographic covariates, to estimate protection against mild/asymptomatic and moderate SARS-CoV-2 infection. RESULTS: Half of the participants (1422) received a booster during October 2023 (280 bivalent, 1142 monovalent), and 536 (19%) had a PCR-confirmed infection over the study period. Bivalent booster VE was 15.1% (-55.4 to 53.6%) at 0-2 months and 4.2% (-46.4 to 37.3%) at 2-4 months post-vaccination. Monovalent booster VE was 44.2% (95% CI 21.7 to 60.3%) at 0-2 months, and 24.1% (-0.7 to 42.9%) at 2-4 months. VE was greater against moderate infection than against mild/asymptomatic infection, but neither booster showed evidence of protection after 4 months. Controlling for vaccination, compared to an infection >2 years prior, infection within the past 6 months was associated with 58.6% (30.3 to 75.4%) increased protection against moderate infection and 38.5% (5.8 to 59.8%) increased protection against mild/asymptomatic infection. CONCLUSIONS: Monovalent XBB.1.5 boosters provided short-term protection against SARS-CoV-2 infection, particularly against moderate symptoms. Vaccine formulations that target the circulating variant may be suitable for inclusion in seasonal vaccination campaigns among HCWs.

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.