Two doses of Covaxin 50% effective against symptomatic covid-19: Lancet
Premium- The study was conducted during India’s second covid-19 surge in a high-exposure population (healthcare workers)
NEW DELHI : Two doses of Bharat Biotech's Covaxin result in 50% effectiveness against symptomatic covid-19, as per the first real-world assessment of the India-developed vaccine, published in The Lancet Infectious Diseases journal. The study was conducted during India’s second covid-19 surge in a high-exposure population (healthcare workers).
The researchers assessed 2,714 hospital workers from the All India Institute of Medical Sciences (AIIMS) in Delhi, India, from April 15 to May 15, 2021, who were symptomatic and underwent RT-PCR testing for covid-19. The delta variant was the dominant strain in India during the study period, accounting for approximately 80% of all confirmed covid-19 cases.
“Our study offers a more complete picture of how Covaxin performs in the field and should be considered in the context of covid-19 surge conditions in India, combined with the possible immune evasive potential of the delta variant. Our findings add to the growing body of evidence that rapid vaccine rollout programmes remain the most promising path to pandemic control while public health policies must continue to include additional protective measures, such as mask-wearing and social distancing," said Dr Manish Soneja, additional professor of Medicine at AIIMS in New Delhi.
Covaxin developed by Bharat Biotech (India), is a vero cell-derived, inactivated whole-virion vaccine administered in a two-dose regimen, 28 days apart. In January 2021, BBV152 was approved for emergency use in India for people aged 18. The World Health Organization (WHO) added covaxin to its list of approved emergency use covid-19 vaccines in November 2021.
The study found that the effectiveness of two vaccine doses remained stable over the seven-week follow-up period. Requests for testing gradually declined toward the end of the study period (from May 6 to May 15). The median interval between receipt of the last vaccine dose and the end of the study period (May 15, 2021) for those who had received one dose was 37 days (range 7 to 119) days and 50 days (range 5 to 103) days for those who had received two doses. The adjusted vaccine effectiveness of the first dose, estimated after 7 and 21 days, was low, which is consistent with the performance of other vaccines against the delta variant and indicates the importance of a second dose to achieve vaccine effectiveness.
The majority of eligible participants were tested for SARS-CoV-2 infection during the first 20 days of the 30-day study when the test positivity rate for covid-19 was at its peak in India. “Findings from the study confirm previous research indicating that two doses of covaxin are required to achieve maximum protection and that all vaccine roll-out plans must follow the recommended dosing schedule. More research is needed to better understand how these findings translate to covaxin’s effectiveness against delta and other variants of concern, especially related to severe covid-19 infection, hospitalisation, and deaths," said Dr Parul Kodan, Assistant Professor of Medicine at AIIMS in New Delhi.
The authors note that several factors may be responsible for the lower vaccine effectiveness in this study. Firstly, this study population only included hospital employees who may have a higher risk of exposure to covid-19 infection than the general population. Secondly, the study was conducted during the peak of India’s second wave of covid-19 with high test positivity rates for both hospital employees and residents of Delhi. Thirdly, the prevalence of circulating variants of concern, especially delta, may have contributed to covaxin’s lower effectiveness.
The authors acknowledge several limitations in the study. Most importantly, this study does not estimate the vaccine effectiveness against hospitalisation, severe disease, and death, which require further assessment. Additionally, the study was not designed to estimate vaccine effectiveness for different time intervals after vaccination or to determine if vaccine effectiveness changed over time. Another limitation was the absence of data on comorbidities and prior covid-19 infection, which may affect health-seeking behaviour as well as vaccine effectiveness.
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