Primary series and booster COVID-19 vaccine effectiveness in a cohort of healthcare workers in Albania during a BA.1 and BA.2 variant period, January - May 2022

BackgroundHealthcare workers (HCWs) have experienced high rates of COVID-19 morbidity and mortality. We estimated COVID-19 two-dose primary series and monovalent booster vaccine effectiveness (VE) against symptomatic SARS-CoV-2 Omicron (BA.1 and BA.2) infection among HCWs in three Albanian hospitals during January-May 2022. MethodsStudy participants completed weekly symptom questionnaires, underwent PCR testing when symptomatic, and provided quarterly blood samples for serology. We estimated VE using Cox regression models (1-hazard ratio), with vaccination status as the time-varying exposure and unvaccinated HCWs as the reference group, adjusting for potential confounders: age, sex, prior SARS-CoV-2 infection (detected by PCR, rapid-antigen test or serology), and household size. ResultsAt the start of the analysis period, 76% of 1,462 HCWs had received a primary series, 10% had received a booster dose, and 9% were unvaccinated; 1,307 (89%) HCWs had evidence of prior infection. Overall, 86% of primary series and 98% of booster doses received were BNT162b2. The median time interval from the second dose and the booster dose to the start of the analysis period was 289 days (IQR:210- 292) and 30 days (IQR:22-46), respectively. VE against symptomatic PCR-confirmed infection was 34% (95%CI: -36;68) for the primary series and 88% (95%CI: 38;98) for the booster. ConclusionsAmong Albanian HCWs, most of whom had been previously infected, COVID-19 booster dose offered improved VE during a period of Omicron BA.1 and BA.2 circulation. Our findings support promoting booster dose uptake among Albanian HCWs, which, as of January 2023, was only 20%.