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Preprint Dans Anglais | medRxiv | ID: ppmedrxiv-22275958


Concerns about the duration of protection conferred by COVID-19 vaccines have arisen in postlicensure evaluations. However, "depletion of susceptibles" bias driven by differential accrual of infection among vaccinated and unvaccinated individuals may contribute to the appearance of waning vaccine effectiveness (VE) in epidemiologic studies, potentially hindering interpretation of estimates. We enrolled California residents who received molecular SARS-CoV-2 tests in a matched, test-negative design case-control study to estimate VE of mRNA-based COVID-19 vaccines between 23 February and 5 December 2021. We analyzed waning protection following 2 vaccine doses using conditional logistic regression models. Additionally, we used data from case-based surveillance along with estimated case-to-infection ratios from a population-based serological study to quantify the potential contribution of the "depletion-of-susceptibles" bias to time-varying VE estimates for 2 doses. We also estimated VE for 3 doses relative to 0 doses and 2 doses, by time since second dose receipt. Pooled VE of BNT162b2 and mRNA-1273 against symptomatic SARS-CoV-2 infection was 91.3% (95% confidence interval: 83.8-95.4%) at 14 days after second-dose receipt and declined to 50.8% (31.2-75.6%) at 7 months. Accounting for differential depletion-of-susceptibles among vaccinated and unvaccinated individuals, we estimated VE was 53.2% (23.6-71.2%) at 7 months among individuals who had completed the primary series (2 doses). With receipt of a third dose of BN162b2 or mRNA-1273, VE increased to 95.0% (82.8-98.6%), compared with zero doses. These findings confirm that observed waning of protection is not attributable to epidemiologic bias and support ongoing efforts to administer additional vaccine doses to mitigate burden of COVID-19.

Preprint Dans Anglais | medRxiv | ID: ppmedrxiv-21267565


ImportanceUnderstanding how SARS-CoV-2 seroprevalence varies regionally across California is critical to the public health response to the pandemic. ObjectiveTo estimate how many Californians have antibodies against SARS-CoV-2 from prior infection or vaccination. DesignWave 1 of CalScope: a repeated cross-sectional serosurvey of adults and children enrolled between April 20, 2021 and June 16, 2021. SettingA population-based random sample of households in seven counties in California (Alameda, El Dorado, Kern, Los Angeles, Monterey, San Diego, and Shasta) were invited to complete an at-home SARS-CoV-2 antibody test and survey instrument. ParticipantsInvitations were sent to 200,000 randomly selected households in the seven counties. From each household, 1 adult (18 years and older) and 1 child (aged 6 months to 17 years) could enroll in the study. There were no exclusion criteria. Main Outcome(s) and MeasuresAll specimens were tested for antibodies against the nucleocapsid and spike proteins of SARS-CoV-2. The primary outcome was serostatus category, which was determined based on antibody test results and self-reported vaccination status: seronegative, antibodies from infection only, antibodies from infection and vaccination, and antibodies from vaccination alone. We used inverse probability of selection weights and iterative proportional fitting to account for non-response. Results11,161 households enrolled in wave 1 of CalScope, with 7,483 adults and 1,375 children completing antibody testing. As of June 2021, 27% (95%CI [23%, 31%]) of adults and 30% (95%CI [24%, 36%]) of children had evidence of prior SARS-CoV-2 infection; 33% (95%CI [28%, 37%]) of adults and 57% (95%CI [48%, 66%]) of children were seronegative. Serostatus varied regionally. Californians 65 years or older were most likely to have antibodies from vaccine alone (59%; 95%CI [48%, 69%]) and children between 5-11 years old were most likely to have antibodies from prior infection alone (36%; 95%CI [21%, 52%]). Conclusions and RelevanceAs of June 2021, a third of adults in California and most children under 18 remained seronegative. Seroprevalence varied regionally and by demographic group, suggesting that some regions or populations might remain more vulnerable to subsequent surges than others. Key PointsO_ST_ABSQuestionC_ST_ABSWhat is the prevalence of vaccine and infection derived antibodies against SARS-CoV-2 in adults and children in California? FindingsIn this population-based serosurvey that included 11,161 households, as of June 2021, 33% of adults and 57% of children were seronegative; 18% of adults and 26% of children had antibodies from infection alone; 9% of adults and 5% of children had antibodies from both infection and vaccination; and 41% of adults and 13% of children had antibodies from vaccination alone. MeaningSerostatus varied considerably across geographic regions, suggesting that certain areas might be at increased risk for future COVID-19 surges.

Preprint Dans Anglais | medRxiv | ID: ppmedrxiv-21266195


BackgroundInformation on the occupational distribution of COVID-19 mortality is limited. ObjectiveTo characterize COVID-19 fatalities among working Californians. DesignRetrospective study of laboratory-confirmed COVID-19 fatalities with dates of death from January 1 to December 31, 2020. SettingCalifornia. ParticipantsCOVID-19 accounted for 8,050 (9.9%) of 81,468 fatalities among Californians 18-64 years old. Of these decedents, 2,486 (30.9%) were matched to state employment records and classified as "confirmed working." The remainder were classified as "likely working" (n=4,121 [51.2%]) or "not working" (n=1,443 [17.9%]) using death certificate and case registry data. MeasurementsWe calculated age-adjusted overall and occupation-specific COVID-19 mortality rates using 2019 American Community Survey denominators. ResultsConfirmed and likely working COVID-19 decedents were predominantly male (76.3%), Latino (68.7%), and foreign-born (59.6%), with high school or less education (67.9%); 7.8% were Black. The overall age-adjusted COVID-19 mortality rate was 30.0 per 100,000 workers (95% confidence interval [CI], 29.3-30.8). Workers in nine occupational groups had mortality rates higher than this overall rate, including those in farming (78.0; 95% CI, 68.7-88.2); material moving (77.8; 95% CI, 70.2-85.9); construction (62.4; 95% CI, 57.7-67.4); production (60.2; 95% CI, 55.7-65.0); and transportation (57.2; 95% CI, 52.2-62.5) occupations. While occupational differences in mortality were evident across demographic groups, mortality rates were three-fold higher for male compared with female workers and three- to seven-fold higher for Latino and Black workers compared with Asian and White workers. LimitationsThe requirement that fatalities be laboratory-confirmed and the use of 2019 denominator data may underestimate the occupational burden of COVID-19 mortality. ConclusionCalifornians in manual labor and in-person service occupations experienced disproportionate COVID-19 mortality, with the highest rates observed among male, Latino, and Black workers.

Preprint Dans Anglais | medRxiv | ID: ppmedrxiv-21265295


BackgroundNon-pharmaceutical interventions (NPIs) are recommended for COVID-19 mitigation. However, the effectiveness of NPIs in preventing SARS-CoV-2 transmission remains poorly quantified. MethodsWe conducted a test-negative design case-control study enrolling cases (testing positive for SARS-CoV-2) and controls (testing negative) with molecular SARS-CoV-2 diagnostic test results reported to California Department of Public Health between 24 February-26 September, 2021. We used conditional logistic regression to assess predictors of case status among participants who reported contact with an individual known or suspected to have been infected with SARS-CoV-2 ("high-risk exposure") within [≤]14 days of testing. Results643 of 1280 cases (50.2%) and 204 of 1263 controls (16.2%) reported high-risk exposures [≤]14 days before testing. Adjusted odds of case status were 2.94-fold (95% confidence interval: 1.66-5.25) higher when high-risk exposures occurred with household members (vs. other contacts), 2.06-fold (1.03-4.21) higher when exposures occurred indoors (vs. not indoors), and 2.58-fold (1.50-4.49) higher when exposures lasted [≥]3 hours (vs. shorter durations) among unvaccinated and partially-vaccinated individuals; excess risk associated with such exposures was mitigated among fully-vaccinated individuals. Mask usage by participants or their contacts during high-risk exposures reduced adjusted odds of case status by 48% (8-72%). Adjusted odds of case status were 68% (32-84%) and 77% (59-87%) lower for partially- and fully-vaccinated participants, respectively, than for unvaccinated participants. Benefits of mask usage were greatest when exposures lasted [≥]3 hours, occurred indoors, or involved non-household contacts. ConclusionsNPIs reduced the likelihood of SARS-CoV-2 infection following high-risk exposure. Vaccine effectiveness was substantial for partially and fully vaccinated persons. KEY POINTSO_LISARS-CoV-2 infection risk was greatest for unvaccinated participants when exposures to known or suspected cases occurred indoors or lasted [≥]3 hours. C_LIO_LIFace mask usage when participants were exposed to a known or suspect case reduced odds of infection by 48%. C_LI

Preprint Dans Anglais | medRxiv | ID: ppmedrxiv-21255135


BackgroundEstimates of COVID-19 vaccine effectiveness under real-world conditions, and understanding of barriers to uptake, are necessary to inform vaccine rollout. MethodsWe enrolled cases (testing positive) and controls (testing negative) from among the population whose SARS-CoV-2 molecular diagnostic test results from 24 February-29 April 2021 were reported to the California Department of Public Health. Participants were matched on age, sex, and geographic region. We assessed participants self-reported history of COVID-19 vaccine receipt (BNT162b2 and mRNA-1273). Participants were considered fully vaccinated two weeks after second dose receipt. Among unvaccinated participants, we assessed willingness to receive vaccination, when eligible. We measured vaccine effectiveness (VE) via the matched odds ratio of prior vaccination, comparing cases with controls. ResultsWe enrolled 1023 eligible participants aged [≥]18 years. Among 525 cases, 71 (13.5%) received BNT162b2 or mRNA-1273; 20 (3.8%) were fully vaccinated with either product. Among 498 controls, 185 (37.1%) received BNT162b2 or mRNA-1273; 86 (16.3%) were fully vaccinated with either product. Two weeks after second dose receipt, VE was 86.8% (95% confidence interval: 68.6-94.7%) and 85.6% (69.1-93.9%) for BNT162b2 and mRNA-1273, respectively. Fully vaccinated participants receiving either product experienced 91.3% (79.7-96.3%) and 68.3% (28.5-86.0%) VE against symptomatic and asymptomatic infection, respectively. Among unvaccinated participants, 42.4% (159/375) residing in rural regions and 23.8% (67/281) residing in urban regions reported hesitancy to receive COVID-19 vaccination. ConclusionsAuthorized mRNA vaccines are effective at reducing documented SARS-CoV-2 infections within the general population of California. Vaccine hesitancy presents a barrier to reaching coverage levels needed for herd immunity. Brief pointsO_LIVaccination is preventing documented SARS-CoV-2 infection in California, with 68% and 91% effectiveness against asymptomatic and symptomatic infection, respectively. C_LIO_LIVaccine effectiveness was equivalent for BNT126b2 and mRNA-1273. C_LIO_LIOnly 66% of unvaccinated participants were willing to receive the vaccine when eligible. C_LI

Preprint Dans Anglais | medRxiv | ID: ppmedrxiv-21254568


Vaccination and non-pharmaceutical interventions (NPIs) reduce transmission of SARS-CoV-2 infection, but their effectiveness depends on coverage and adherence levels. We used scenario modeling to evaluate their effects on cases and deaths averted and herd immunity. NPIs and vaccines worked synergistically in different parts of the pandemic to reduce disease burden.

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