Lancet study shows Bharat Biotech's COVID-19 vaccine is 50% effective

A new study published in The Lancet finds that Bharat Biotech’s Covaxin is 50% effective against symptomatic COVID-19, lower than the vaccine’s published Phase 3 clinical trial efficacy results, which showed it to be 77.8% effective against symptomatic COVID-19.

It’s the “first real-world study” on the vaccine’s effectiveness against symptomatic COVID-19, and took place from April to May 2021. The vaccine was given to employees of the All India Institute of Medical Sciences, a tertiary care hospital and COVID-19 treatment center in New Delhi.

Why it matters: Real-world assessments of vaccine effectiveness often differ from controlled, clinical trial conditions, for which efficacy data is based on.

Experts commenting on the study, however, said the decline is “neither surprising nor exclusive” to Covaxin. The Delta variant is known to be highly transmissible, and other studies have shown reduced effectiveness of other COVID-19 vaccines against the Delta variant.

What are the caveats? The authors identified several factors that may have contributed to the vaccine’s lower effectiveness in their study, such as the study population potentially having a higher risk of exposure to COVID-19 as they work in a hospital, and the study being conducted during the peak of the India’s deadly second COVID-19 wave — during which the positivity rate in Delhi was around 35%. The Delta variant was also the dominant COVID-19 strain in the country at that time, although the study did not determine the variants affecting patients.

The study does not provide an estimate on the vaccine’s effectiveness against hospitalization, severe disease, and death. The study also did not have data on patients’ comorbidities and if they previously had a COVID-19 infection, which “may affect health-seeking behaviour as well as vaccine effectiveness,” according to a news release.