Effectiveness of Four Vaccines in Preventing SARS-CoV-2 Infection in Kazakhstan

BACKGROUND

In February 2021 Kazakhstan began offering COVID-19 vaccines to adults. Breakthrough SARS-CoV-2 infections raised concerns about real-world vaccine effectiveness. We aimed to evaluate effectiveness of four vaccines against SARS-CoV-2 infection.

METHODS

We conducted a retrospective cohort analysis among adults in Almaty using aggregated vaccination data and individual-level breakthrough COVID-19 cases (≥14 days from 2 ^nd dose) using national surveillance data. We ran time-adjusted Cox-proportional-hazards model with sensitivity analysis accounting for varying entry into vaccinated cohort to assess vaccine effectiveness for each vaccine (measured as 1-adjusted hazard ratios) using the unvaccinated population as reference (N=565,390). We separately calculated daily cumulative hazards for COVID-19 breakthrough among vaccinated persons by age and vaccine month.

RESULTS

From February 22 to Sept 1, 2021 in Almaty, 747,558 (57%) adults were fully vaccinated (received 2 doses) and 108,324 COVID-19 cases (11,472 breakthrough) were registered. Vaccine effectiveness against infection was 78% (sensitivity estimates: 74–82%) for QazVac, 77% (72– 81%) for Sputnik V, 71% (69–72%) for Hayat-Vax, and 69% (64–72%) for CoronaVac. Among vaccinated persons, the 90-day follow-up cumulative hazard for breakthrough infection was 2.2%. Cumulative hazard was 2.9% among people aged ≥60 years versus 1.9% among persons aged 18–39 years (p<0.001), and 1.2% for people vaccinated in February–May versus 3.3% in June–August (p<0.001).

CONCLUSION

Our analysis demonstrates high effectiveness of COVID-19 vaccines against infection in Almaty similar to other observational studies. Higher cumulative hazard of breakthrough among people >60 years of age and during variant surges warrants targeted booster vaccination campaigns.

What is already known on this topic

• Plenty of data are published on effectiveness of mRNA vaccines; however, these vaccines were not widely available in many low- and middle-income countries in 2021.

• There are no real-world effectiveness studies on several vaccines available in the Central Asia region, including QazVac vaccine, an inactivated vaccine developed by Kazakhstan.

• Understanding how these vaccines are performing outside of clinical trials is critical for the COVID-19 response and lack of published data can contribute to vaccine hesitancy.

What this study adds

• Our study demonstrated that at the population-level the four vaccines against COVID-19 used in Kazakhstan were effective at preventing SARS-CoV-2 infection.

• Vaccination reduced the risk of infection by 76% and prevented over 100,000 cases of SARS-CoV-2 infection in Almaty, the country’s most populous city.

• This is also the first study that demonstrated high vaccine effectiveness in real-world conditions of QazVac, developed in Kazakhstan.

How this study might affect research, practice or policy

• Policy makers in Kazakhstan and the Central Asia region need data on vaccines provided in the region to update evidence-based vaccine guidelines for different populations.