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Primary Series COVID-19 Vaccine Effectiveness Among Health Care Workers in Albania, February–December 2021
34 Pages Posted: 7 Dec 2022
More...Abstract
Background: Healthcare workers (HCWs) have experienced high rates of morbidity and mortality from COVID-19.
Methods: We conducted a prospective cohort study among HCWs in three Albanian hospitals between February 19 and December 14, 2021. All underwent PCR and serology testing at enrolment, regular serology throughout, and PCR testing when symptomatic. We estimated vaccine effectiveness (VE) against PCR-confirmed symptomatic COVID-19, and against all SARS-CoV-2 infections (symptomatic or asymptomatic), measured by PCR and/or seroconversion. VE was estimated using a Cox regression model, with vaccination status as a time-varying variable, adjusting for a priori fixed covariates, and considered potential confounders that changed the VE estimate by more than 5%.
Findings: We enrolled 1504 HCWs; 70% had evidence of prior SARS-CoV-2 infection. By the end of the analysis period, 1220 (82%) participants had completed a primary vaccine series. VE against COVID-19 was 65·1% (95% CI 37·7–80·5); 58·2% (95% CI 15·7–79·3) among participants without prior SARS-CoV-2 infection; and 73·6% (95% CI 24·3–90·8) among previously-infected participants. For BNT162b2 only, VE was 69·5% (95% CI 44·5–83·2). During the Delta variant-predominant period, VE was 67·1% (95% CI 38·3–82·5). VE against SARS-CoV-2 infection for the full study period was 36·9% (95% CI 15·8–52·7).
Interpretation: We found moderate primary-series VE against COVID-19 among HCWs in Albania. Our results support the continued promotion of COVID-19 vaccine in Albania, and highlight the benefit of vaccination in populations with high levels of prior infection.
Trial Registration Details: The study is also registered with clinicaltrials.gov (Identifier NCT04811391).
Funding Information: This study was supported by the World Health Organization/European Regional Office, US Centers for Disease Control and Prevention.
Declaration of Interests: None.
Ethics Approval Statement: The study protocol was approved by the WHO Ethical Review Board (ERC) (reference number CERC.0097A) and the Albania IPH ERC (reference number 156). The CDC humans review determined the activity to be a public health evaluation. All participants provided written informed consent
Keywords: COVID-19, COVID-19 vaccine, vaccine effectiveness, hybrid immunity, SARS-CoV-2, healthcare workers, Albania, Delta variant
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