Relative vaccine effectiveness of a CoronaVac booster dose in preventing symptomatic SARS-CoV-2 infection among healthcare workers during an Omicron period in Azerbaijan, January–August 2022

Among Azerbaijani healthcare workers (HCWs), compared to primary vaccine series, CoronaVac booster relative vaccine effectiveness was 60% (95% CI:25–79) and 79% (95% CI:44–92) against symptomatic and medically attended illness, respectively, during an Omicron BA.1/BA.2 period. Our results support timely CoronaVac booster uptake among Azerbaijani HCWs to reduce morbidity. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This study was funded by The 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 was approved by the WHO Research Ethics Review Committee (protocol: CERC.0097C) and the Ethics Committee of Azerbaijan State Academy of Physical Culture and Sport (March 3, 2021; Protocol #3/21). All participants provided informed, written consent. The study is registered in the [clinicaltrails.gov][1] registry (NCT050694). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the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 The data are not publicly available due to privacy or ethical restrictions. The authors do not have consent from study participants to share the data. [1]: http://clinicaltrails.gov