Covaxin, one of the main vaccines used in India's coronavirus immunization drive, provides only 50% protection against symptomatic COVID-19, according to a real-world study that suggests the shot is less effective than initially thought.
As India was slammed by its second major Covid wave earlier this year, researchers at the All India Institute of Medical Sciences in Delhi analyzed data from 2,714 of the hospital's health workers who were showing signs of infection and underwent RT-PCR testing between April 15 and May 15, according to a study published in The Lancet Infectious Diseases journal. At the start of the country's vaccination campaign in January, staff at AIIMS had exclusively been offered Covaxin, a shot co-developed by India's state-funded health research agency and local company Bharat Biotech International Ltd.
The authors found that two weeks or more after completing a two-dose regime the vaccine's adjusted effectiveness against symptomatic Covid was lower than the 77.8% that interim results established during final stage tests, a study of which was published in The Lancet earlier this month. High infection rates and virus exposure among the hospital's employees may have contributed to Covaxin's weaker real-world efficacy, along with the possibility that the then recently emerged delta variant blunted the shot's protection, the researchers said.
"Our study offers a more complete picture of how BBV152 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," Manish Soneja, an additional professor of medicine at AIIMS in New Delhi, said in a statement referring to the vaccine's scientific name.
While various studies indicate almost all Covid vaccines show reduced effectiveness against the highly infectious delta variant, which began its rampant spread across India in early 2021, the new research on Covaxin may dent the inoculation's appeal at a time when Bharat Biotech is scaling up manufacturing and as India restarts overseas vaccine shipments.
So far more than 130 million doses of Covaxin have been administered in India. Bharat Biotech and the government, which has widely promoted the shot, have sought to close the door on controversies involving the vaccine's early authorization in January before it had completed phase 3 human trials, prompting widespread hesitancy in the country at the time.
The World Health Organization's independent technical panel also took months before granting emergency approval to Covaxin in early November, repeatedly asking Bharat Biotech for further data. Krishna Ella, chairman of the Hyderabad-based vaccine maker, said the WHO green light took as long as it did because of criticism surrounding the shot, which was developed using traditional inactivated-virus technology.
The researchers said the AIIMs study didn't estimate the vaccine's effectiveness against hospitalization, severe disease and death, while acknowledging that it wasn't designed to estimate protection over different time intervals. Patients weren't tested to find if they were symptomatic due to a specific variant and the authors also pointed to the lack of data on comorbidities and prior infections.