COVID­19 vaccines effectiveness against symptomatic SARS­CoV­2 Delta variant infection: a population­based case­control study in St. Petersburg, Russia

Background : Studies of mRNA and vector­based vaccines used in different countries report acceptable levels of effectiveness against SARS­CoV­2 infection caused by the Delta variants of SARS­CoV­2. No studies estimated vaccine effectiveness (VE) of Gam­COVID­Vac and other vaccines used in Russia against symptomatic infection with Delta variant. In this population­based case­control study, we aimed to estimate the effectiveness of the Russian COVID­19 vac­ cines against symptomatic SARS­CoV­2 during the recent outbreak caused by the Delta VOC in October 2021 in St. Petersburg, Russia. Methods : In a population­based case­control study with density sampling of controls, we acquired information on cases and controls from two independent studies conducted in St. Petersburg. Cases were symptomatic patients with confirmed SARS­CoV­2 (using polymerase chain reaction (PCR) test) referred to low­dose computed tomography (LDCT) triage in two outpatient centres between October 6 and 14, 2021 during the Delta variant outbreak. We recruited the controls during the representative survey of the seroprevalence study conducted during the same period in St. Petersburg using random digit dialling. In the primary analysis, we used logistic regression models to estimate the adjusted (age, gender, and history of confirmed COVID­19) VE against symptomatic SARS­CoV­2 resulted in a referral to triage centre for three vaccines used in Russia: Gam­COVID­Vac, EpiVacCorona, and CoviVac. Findings : We included 1,198 cases and 2,747 controls recruited between the 6th and 14th of October in the final analysis. VE was 58% (95% CI: 50–64) for Gam­COVID­Vac (Sputnik V), 50% (95% CI: 30–64) for 1­dose Gam­COVID­Vac (Sputnik V) or Sputnik Light, ­40% (95% CI: ­191–33) for EpiVacCorona and 38% (95% CI: 0–62) for CoviVac. Without adjustment for the history of confirmed COVID­19 VE for all vaccines was lower, except for one­dose Gam­ COVID­Vac (Sputnik Light). The adjusted VE was slightly lower in women — 52% (95% CI: 41–62) than men — 66% (95% CI: 55–74). It was also higher in younger age. However, in the analysis restricted to participants without a history of confirmed COVID­19, the differences in VE by age group were smaller. Interpretation : In contrast to other Russian vaccines, Gam­COVID­Vac is effective against symptomatic SARS­CoV­2 infection caused by Delta VOC. Effec­ tiveness is likely higher than the estimated 58% due to bias arising from high prevalence of the past COVID­19 in St. Petersburg. Funding : Population­based survey in St. Petersburg was funded by Polymetal International, plc.