Vaccine effectiveness of CanSino (Adv5-nCoV) COVID-19 vaccine among childcare workers – Mexico, March–December 2021

Background Beginning in March 2021, Mexico vaccinated childcare workers with a single-dose CanSino Biologics (Adv5-nCoV) COVID-19 vaccine. Although CanSino is currently approved for use in 10 Latin American, Asian, and European countries, little information is available about its vaccine effectiveness (VE). Methods We evaluated CanSino VE within a childcare worker cohort that included 1,408 childcare facilities. Participants were followed during March–December 2021 and tested through SARS-CoV-2 RT-PCR or rapid antigen test if they developed any symptom compatible with COVID-19. Vaccination status was obtained through worker registries. VE was calculated as 100% × (1−hazard ratio for SARS-CoV-2 infection in fully vaccinated vs. unvaccinated participants), using an Andersen-Gill model adjusted for age, sex, state, and local viral circulation. Results The cohort included 43,925 persons who were mostly (96%) female with a median age of 32 years; 37,646 (86%) were vaccinated with CanSino. During March–December 2021, 2,250 (5%) participants had laboratory-confirmed COVID-19, of whom 25 were hospitalized and 6 died. Adjusted VE was 20% (95% CI = 10–29%) against illness, 76% (42–90%) against hospitalization, and 94% (66–99%) against death. VE against illness declined from 48% (95% CI = 33–61) after 14–60 days following full vaccination to 20% (95% CI = 9–31) after 61–120 days. Conclusions CanSino vaccine was effective at preventing COVID-19 illness and highly effective at preventing hospitalization and death. It will be useful to further evaluate duration of protection and assess the value of booster doses to prevent COVID-19 and severe outcomes. Summary We evaluated CanSino (Adv5-nCoV) COVID-19 vaccine effectiveness during March–December 2021 using a childcare worker cohort that included 43,925 participants across Mexico. Vaccination decreased the risk of COVID-19 illness by 20%, hospitalization by 76%, and death by 94%. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This evaluation has been funded through the IMSS, Government of Mexico. ### 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 Instituto Mexicano del Seguro Social waived ethical approval for this work as the evaluation was a non-research, public health surveillance activity and both data collection and illness tracking were a requirement for working in these childcare centers during the pandemic. 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 and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes Data produced in the present study are available upon reasonable request to the authors.