ABSTRACT
We estimated vaccine effectiveness (VE) of SARS-CoV-2 Omicron XBB.1.5 vaccination against self-reported infection between 9 October 2023 and 9 January 2024 in 23,895 XBB.1.5 vaccine-eligible adults who had previously received at least one booster. VE was 41% (95%CI:23-55) in 18-59-year-olds and 50% (95%CI:44-56) in 60-85-year-olds. Sequencing data in a subset of infections suggests immune escape of the emerging BA.2.86 (JN.1) variant from recent prior infection (OR:2.6; 95%CI:1.1-6.3) and, although not statistically significant, from XBB.1.5 vaccination (OR:1.6; 95%CI:0.9-2.9).
ABSTRACT
We present early vaccine effectiveness (VE) estimates of the 2023 seasonal COVID-19 vaccination campaign using XBB.1.5 vaccine against COVID-19 hospitalization and ICU admission in previously vaccinated adults [≥]60 years old in the Netherlands. We compared vaccination status of 2050 hospitalizations including 92 ICU admissions with age group-, sex-, region- and date-specific population vaccination coverage between 9 October and 5 December 2023. VE against hospitalization was 70.7% (95% CI: 66.6; 74.3), VE against ICU admission was 73.3% (95% CI: 42.2; 87.6).
Subject(s)
COVID-19ABSTRACT
Background Information on the magnitude and duration of antibody levels after COVID-19 vaccination in different groups may be useful for prioritizing of additional vaccinations. Methods Serum samples were collected every six months in a prospective cohort study among adults in the Netherlands. Geometric mean concentrations (GMCs) of antibodies against the receptor binding domain of the SARS-CoV-2 spike protein were calculated after the primary series, first, and second booster vaccinations. Effects of age (18-59 vs 60-85 years) and medical risk conditions on GMC 2-6 weeks and 21-25 weeks after each vaccination, and on waning during 3-25 weeks after each vaccination, were estimated by linear regression. Results We included 20,816, 16,820 and 5,879 samples collected after primary, first and second booster vaccination, respectively. GMCs at 2-6 and 21-25 weeks after primary series were lower in participants with older age or medical risk conditions. After the first booster, older age was associated with lower GMC at 2-6 weeks, higher GMC at 21-25 weeks, and slower waning. GMCs or waning after the first and second boosters (only 60-85) were not associated with medical risk conditions. Conclusions Since antibody differences by age and medical risk groups have become small with increasing number of doses, other factors such as disease severity rather than antibody levels are useful for prioritization of additional vaccinations.
Subject(s)
COVID-19ABSTRACT
Background: Registration in the Dutch national COVID-19 vaccination register requires consent from the vaccinee. This causes misclassification of non-consenting vaccinated persons as being unvaccinated. We quantified and corrected the resulting information bias in the estimation of vaccine effectiveness (VE). Methods: National data were used for the period dominated by the SARS-CoV-2 Delta variant (11 July to 15 November 2021). VE ((1-relative risk)*100%) against COVID-19 hospitalization and ICU admission was estimated for individuals 12-49, 50-69, and [≥]70 years of age using negative binomial regression. Anonymous data on vaccinations administered by the Municipal Health Services were used to determine informed consent percentages and estimate corrected VEs by iterative data augmentation. Absolute bias was calculated as the absolute change in VE; relative bias as uncorrected / corrected relative risk. Results: A total of 8,804 COVID-19 hospitalizations and 1,692 COVID-19 ICU admissions were observed. The bias was largest in the 70+ age group where the non-consent proportion was 7.0% and observed vaccination coverage was 87%: VE of primary vaccination against hospitalization changed from 75.5% (95% CI 73.5-77.4) before to 85.9% (95% CI 84.7-87.1) after correction (absolute bias -10.4 percentage point, relative bias 1.74). VE against ICU admission in this group was 88.7% (95% CI 86.2-90.8) before and 93.7% (95% CI 92.2-94.9) after correction (absolute bias -5.0 percentage point, relative bias 1.79). Conclusions: VE estimates can be substantially biased with modest non-consent percentages for registration of vaccination. Data on covariate specific non-consent percentages should be available to correct this bias.
Subject(s)
COVID-19ABSTRACT
We used data of 32,542 prospective cohort study participants who previously received primary and one or two monovalent booster COVID-19 vaccinations. Between 26 September and 19 December 2022, relative effectiveness of bivalent Original/Omicron BA.1 vaccination against self-reported Omicron SARS-CoV-2 infection was 31% in 18-59-year-olds and 14% in 60-85-year-olds. Protection was higher after prior Omicron infection than after bivalent vaccination without prior infection. Although bivalent booster vaccination increases protection against COVID-19 hospitalizations, we found limited added benefit in preventing SARS-CoV-2 infection.
Subject(s)
COVID-19ABSTRACT
Introduction. We aimed to estimate vaccine effectiveness against infection (VE-infection) and infectiousness (VE- infectiousness) in a household setting during Delta and Omicron. Knowing these effects can aid policy makers in deciding which groups to prioritize for vaccination. Methods. Participants with a positive SARS-CoV-2 test were asked about COVID-19 vaccination status and SARS-CoV-2 testing of their household members one month later. VE-infection and VE-infectiousness was estimated using GEE logistic regression adjusting for age and vaccination status, calendar week and household size. Results. 3,409 questionnaires concerning 4,123 household members were included. During the Delta-period, VE-infection of primary series was 47% (95% CI: -27%-78%) and VE-infectiousness of primary series was 70% (95% CI: 28%-87%). During the Omicron-period, VE-infection was -36% (95% CI: -88%-1%) for primary series and -30% (95% CI: -80%-6%) for booster vaccination. The VE-infectiousness was 45% (95% CI: -14%-74%) for primary series and 64% (95% CI: 31%-82%) for booster vaccination. Discussion. Our study shows that COVID-19 vaccination is effective against infection with SARS-CoV-2 Delta and against infectiousness of SARS-CoV-2 Delta and Omicron. Estimation of VE against infection with SARS-CoV-2 Omicron was limited by several factors. Our results support vaccination for those in close contact with vulnerable people to prevent transmission.
Subject(s)
COVID-19 , InfectionsABSTRACT
Introduction - Monitoring of COVID-19 vaccine effectiveness (VE) is needed to inform vaccine policy. We estimated VE of primary vaccination, and first and second booster vaccination, against SARS-CoV-2 infection overall, and in four risk groups defined by age and medical risk condition, in the Delta and Omicron BA.1/BA.2 periods. Methods - VASCO is an ongoing prospective cohort study among vaccinated and unvaccinated Dutch adults. The primary endpoint was a self-reported positive SARS-CoV-2 test during 12 July 2021-6 June 2022. Participants with a prior SARS-CoV-2 infection, based on a positive test or serology, were excluded. We used Cox proportional hazard models with vaccination status as time-varying exposure and adjustment for age, sex, educational level, and medical risk condition. We stratified by Delta and Omicron BA.1/BA.2 periods, risk group, and time since vaccination. Results - 37,170 participants (mean age 57 years) were included. In the Delta period, VE <6 weeks after primary vaccination was 80% (95%CI 69-87) and decreased to 71% (65-77) after 6 months. VE increased to 96% (86-99) shortly after the first booster vaccination. In the Omicron period these estimates were 46% (22-63), 25% (8-39) and 57% (52-62), respectively. VE was 50% (34-62) <6 weeks after a second booster vaccination in participants aged [≥]60 years. For the Omicron period, an interaction term between vaccination status and risk group significantly improved the model (p<0.001), with generally lower VEs for those with a medical risk condition. Conclusions - Our results show the benefit of booster vaccinations against infection, also in risk groups, although the additional protection wanes quite rapidly.
Subject(s)
COVID-19ABSTRACT
Objectives: To estimate the protective effect of previous infections and vaccinations on SARS-CoV-2 Omicron infection. Design: Prospective cohort study Setting: Community-based cohort, the Netherlands Participants: 43,257 Community-dwelling adults aged 18-85 years contributed 8,291,966 person-days between 10 January 2022 and 1 September 2022. Main outcome measures: SARS-CoV-2 infection, defined as either a reported positive (self-administered) antigen or PCR test, or seroconversion or 4-fold increase in Nucleoprotein-antibodies, based on 6-monthly serum samples. Cox proportional hazard models were used with SARS-CoV-2 infection and any COVID-19 vaccination as time-varying exposures, calendar time as underlying time scale and adjustment for age, sex, medical risk and educational level. Results: In participants with 2, 3 or 4 prior immunizing events (vaccination or previous infection), we found a relative reduction of 71-85% in Omicron infection in weeks 4-10 post-last event with hybrid immunity compared to vaccine-induced immunity. Differences in risk of infection were partly explained by differences in anti-Spike RBD (S) antibody concentration, which showed a similar pattern but with smaller differences between vaccine-induced and hybrid immunity. Compared to the lowest quartile, participants in subsequent quartiles of S-antibody concentrations had 19%, 35% and 71% reduced risk of infection, respectively. Among participants with hybrid immunity, with one previous pre-Omicron infection, there was no relevant difference in risk of Omicron infection by sequence of vaccination(s) and infection). Regardless of the type of previous immunizing events, additional events increased the protection against infection, but not above the level of the first weeks after the previous event. Conclusions: Our results showed that hybrid immunity is more protective against infection with SARS-CoV-2 Omicron than vaccine-induced immunity, up to at least 30 weeks after the last immunizing event. Among those with hybrid immunity, the sequence and number of immunizing events was not found to be of importance, and its protective effect was partly explained by circulating S-antibodies. In our population with a high level of immunity, additional immunizing events reduced risk of infection with Omicron variants only temporarily. Trial registration: Dutch Trial Register (NTR), registration number NL9279 (available via ICTRP Search Portal (who.int))
Subject(s)
COVID-19 , Severe Acute Respiratory SyndromeABSTRACT
Background: Vaccines against COVID-19 have proven effective in preventing COVID-19 hospitalisation. In this study, we aimed to quantify one aspect of the public health impact of COVID-19 vaccination by estimating the number of averted hospitalisations. We present results from the beginning of the vaccination campaign (period 1, January 6, 2021) and a period starting at August 2, 2021 (period 2) when all adults had the opportunity to complete their primary series, until August 30, 2022. Methods Using calendar-time specific vaccine effectiveness (VE) estimates and vaccine coverage (VC) by round (primary series, first booster and second booster) and the observed number of COVID-19 associated hospitalisations, we estimated the number of averted hospitalisations per age group for the two study periods. From January 25, 2022, when the indication of hospitalisation was registered, hospitalisations not causally related to COVID-19 were excluded. Results In period 1, there were an estimated 98,170 (95% confidence interval (CI) 96,123-99,928) averted hospitalisations, of which 90,753 (95% CI 88,790-92,531) in period 2, equalling 57.0% and 67.9% of all hospital admissions. Estimated averted hospitalisations were lowest for 12-49-year-olds and highest for 70-79-year-olds. More admissions were averted in the Delta period (72.2%) than in the Omicron period (64.0%). Conclusion COVID-19 vaccination prevented a large number of hospitalisations. Although the estimated number of hospitalisations during the study period could not have occurred realistically due to limits on health care, these findings underline the public health importance of the vaccination campaign to policy makers and the public.
Subject(s)
COVID-19ABSTRACT
We investigate differences in protection from previous infection and/or vaccination against infection with Omicron BA.4/5 or BA.2. We observed a higher percentage of registered previous SARS-CoV-2 infections among 19836 persons infected with Omicron BA.4/5 compared to 7052 persons infected with BA.2 (31.3% vs. 20.0%) between 2 May and 24 July 2022 (adjusted odds ratio (aOR) for testing week, age group and sex: 1.4 (95%CI: 1.3-1.5)). No difference was observed in the distribution of vaccination status between BA.2 and BA.4/5 cases (aOR: 1.1 for primary and booster vaccination). Among reinfections, those newly infected with BA4/5 had a shorter interval between infections and the previous infection was more often caused by BA.1, compared to those newly infected with BA.2 (aOR: 1.9 (1.5-2.6). This suggests immunity induced by BA.1 is less effective against a BA.4/5 infection than against a BA.2 infection.
Subject(s)
Severe Acute Respiratory Syndrome , COVID-19ABSTRACT
Background: We aimed to estimate vaccine effectiveness (VE) against COVID-19 mortality, and to explore whether an increased risk in non-COVID-19 mortality exists in the weeks following a COVID-19 vaccine dose. Methods: National registries of causes of death, COVID-19 vaccination and long-term care reimbursements were linked by a unique identifier using data from 1 January 2021 to 31 January 2022. We used Cox regression with calendar time as underlying time scale to, firstly, estimate VE against COVID-19 mortality after primary and first booster vaccination, per month since vaccination and, secondly, estimate risk of non-COVID-19 mortality in the 8 weeks following a first, second or booster dose, adjusting for birth year, sex and country of origin. Results: VE against COVID-19 mortality was >90% for all age groups two months after completion of the primary series. VE gradually decreased thereafter, to around 80% at 7-8 months post-primary series for most groups, and around 60% for elderly receiving a high level of long-term care and for people aged 90+ years. The risk of non-COVID-19 mortality was lower or similar in the 8 weeks following a first booster dose compared to no vaccination, first or second dose, respectively, for all age and long-term care groups. Conclusion: COVID-19 vaccination greatly reduced the risk of COVID-19 mortality and no increased risk of death from other causes was seen at the population level.
Subject(s)
COVID-19 , DeathABSTRACT
Given the emergence of the SARS-CoV-2 Omicron BA.1 variant and the roll-out of booster COVID-19 vaccination, evidence is needed on protection conferred by primary vaccination, booster vaccination and previous SARS-CoV-2 infection against Omicron BA.1 compared with Delta infection. We employed a test-negative design and used multinomial logistic regression on data from community PCR testing in the Netherlands, from 22 November 2021 to 19 January 2022. S-gene target failure (SGTF) was used as proxy for Omicron BA.1 infection versus Delta. A total of 528,488 tests were included, of which 38,975 SGTF and 41,245 non-SGTF infections. Protection from primary vaccination was 25% (95% confidence interval (CI): 21-29) and from previous infection 33% (95% CI: 31-35) against Omicron BA.1 infection. Protection against Delta infection was higher with 76% (95% CI: 75-76) for primary vaccination and 78% (95% CI: 76-80) for previous infection. Higher protection was observed in individuals with both primary vaccination and earlier infection compared with either one. Waning of vaccine- or infection-induced protection over time was observed against both variants. Booster vaccination considerably increased vaccine effectiveness against Omicron BA.1 to 76% (95% CI: 72-79) and 68% (95% CI: 67-69) with and without previous infection, respectively. Primary vaccination with current COVID-19 vaccines and pre-Omicron SARS-CoV-2 infections offer low protection against Omicron BA.1 infection. Booster vaccination considerably increases protection against Omicron BA.1, although protection remains lower than against Delta.
Subject(s)
COVID-19 , Severe Acute Respiratory Syndrome , Hepatitis DABSTRACT
We estimated vaccine effectiveness against onward transmission by comparing secondary attack rates among household members between vaccinated and unvaccinated index cases, based on source and contact tracing data collected when Delta variant was dominant. Effectiveness of full vaccination of the index against transmission to fully vaccinated household contacts was 40% (95% confidence interval (CI) 20-54%), which is in addition to the direct protection of vaccination of contacts against infection. Effectiveness of full vaccination of the index against transmission to unvaccinated household contacts was 63% (95%CI 46-75%). We previously reported effectiveness of 73% (95%CI 65-79%) against transmission to unvaccinated household contacts for the Alpha variant.
ABSTRACT
The objective of this study was to estimate vaccine effectiveness (VE) against COVID-19 hospitalization and ICU admission, per period according to dominating SARS-CoV-2 variant (Alpha and Delta), per vaccine and per time since vaccination. To this end, data from the national COVID-19 vaccination register was added to the national register of COVID-19 hospitalizations. For the study period 4 April - 29 August 2021, 15,571 hospitalized people with COVID-19 were included in the analysis, of whom 887 (5.7%) were fully vaccinated. Incidence rates of hospitalizations and ICU admissions per age group and vaccination status were calculated, and VE was estimated as 1-incidence rate ratio, adjusted for calendar date and age group in a negative binomial regression model. VE against hospitalization for full vaccination was 94% (95%CI 93-95%) in the Alpha period and 95% (95%CI 94-95%) in the Delta period. The VE for full vaccination against ICU admission was 93% (95%CI 87-96%) in the Alpha period and 97% (95%CI 97-98%) in the Delta period. VE was high in all age groups and did not show waning with time since vaccination up to 20 weeks after full vaccination.