Abstract
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%) femal e 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.
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