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

Background Healthcare 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. Methods Study 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. Results At 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. Conclusions Among 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%. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This study was funded by Task Force for Global Health and World Health Organisation Regional Office for Europe. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The study protocol was approved by the WHO Research Ethics Review Committee (ERC) (reference number CERC.0097A) and the Albania IPH ERC (reference number 156). This activity was determined to meet the requirements of public health surveillance as defined in 45 CFR 46.102(l) (2) (CDC reference number 0900f3eb81ce0ede). All participants provided written informed consent. The study is registered with clinicaltrials.gov (Identifier [NCT04811391][1]). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors. [1]: /lookup/external-ref?link_type=CLINTRIALGOV&access_num=NCT04811391&atom=%2Fmedrxiv%2Fearly%2F2023%2F05%2F05%2F2023.05.05.23289503.atom