​Covaxin Was 50% Effective Against Symptomatic Covid During Second Wave: Real-​World Study In AIIMS

​A real-world study assessed 2,714 AIIMS workers and found the adjusted vaccine effectiveness of ​Bharat Biotech's ​BBV152 against symptomatic Covid-19 to be 50% after 2 doses of Covaxin.

Representative image of Covaxin vials | Photo: Getty

New Delhi​: Two doses of Bharat Biotech's COVAXIN (BBV152) are 50 per cent effective against symptomatic Covid-19, suggests the first real-world study of the vaccine. 

Real world studies investigat​e the health interventions whose design does not follow that of a highly-controlled randomised controlled trial (RCT). Also, real​-world studies aim to reflect health intervention effectiveness in routine clinical practice. 

The real-world study of BBV152 ​has been published in The Lancet Infectious Diseases Journal. As many as 2,714 hospital workers from the All India Institute of Medical Sciences (AIIMS), Delhi, India were assessed from April 15 to May 15, 2021, as part of this study. These workers were symptomatic for Covid-19, and underwent RT-PCR testing. During the time the study was conducted, the Delta variant was the dominant strain in India. Around 80 per cent of all confirmed Covid-19 cases in India were attributed to the Delta variant.

In January 2021, BBV152 was approved for emergency use in India for people aged 18 and above. 

An interim analysis of the Phase III controlled trials for BBV152 showed that two doses of the vaccine provide 77.8 per cent protection against symptomatic Covid-19, two weeks after receiving the second dose. Following this, the vaccine received emergency use approval from the World Health Organization (WHO) for people aged 18 and older, in November 2021.

BBV152 is India's first indigenous, whole-virion, inactivated vaccine developed by Bharat Biotech in collaboration with the Indian Medical Research Council (ICMR) and the National Institute of Virology (NIV) for the treatment of Covid-19. 

BBV152 is Vero cell-derived, and is formulated with a novel adjuvant. It is administered in two doses, with a gap of 28 days between the first and second doses.

Evaluating The Real-World Effectiveness Of BBV152

The new study was conducted during India's second Covid-19 surge on healthcare workers, who constitute a high-exposure population. Also, the BBV152 vaccine was primarily offered to them. This presented a unique opportunity to evaluate the real-world effectiveness of the vaccine, ​The Lancet ​said in a ​statement. 

Dr Manish Soneja, Additional Professor of Medicine at AIIMS in New Delhi, said the study offers a more complete picture of how BBV152 performs in the field. He said the findings add to the body of evidence that vaccine rollout programmes are the most promising path to pandemic control. Public health policies must continue to include additional protective measures, such as mask-wearing and social distancing, he noted.

AIIMS has exclusively offered BBV152 to all of its 23,000 employees since January 16, 2021. 

Between April 15 and May 15, 2021, as many as 2,714 employees participants were involved in the study population, to evaluate the effectiveness of BBV152 vaccine against symptomatic RT-PCR confirmed SARS-CoV-2 infection. In the study population, as many as 1,617 people tested positive for SARS-CoV-2 infection, while 1,097 persons tested negative. The negative RT-PCR tests were considered as controls, and were matched with the positive cases, using 1:1 ratio based on age and gender. 

The probabilities of effectiveness of BBV152 were compared between cases and controls. The vaccine effectiveness was adjusted for occupational exposure to Covid-19, previous SARS-CoV-2 infection, and infection dates, the study ​said. 

Adjusted Vaccine Effectiveness Against Symptomatic Covid-19 Is 50 per cent

The study found the adjusted vaccine effectiveness of BBV152 against symptomatic Covid-19 to be 50 per cent, after two doses, with the second dose being administered 14 or more days before undergoing RT-PCR testing.

The effectiveness of the vaccine was observed to remain stable over a follow-up period of seven weeks.

The test positivity rate for Covid-19 was at its peak in India during the study period. From May 6 to May 15, the requests for testing declined. 

The adjusted vaccine effectiveness of the first dose was estimated after seven and 21 says. It was observed to be low, which is consistent with the performance of other vaccines against the Delta variant. This indicates the importance of a second dose to achieve vaccine effectiveness, mentions the study.

Dr Parul Kodan, Assistant Professor of Medicine at AIIMS in New Delhi, said ​in The Lancet statement that ​the findings from the study confirm previous research that indicated the need for two doses of BBV152 to achieve maximum protection. The findings also confirmed previous research which stated that all vaccine roll-out plans must follow the recommended dosing schedule, she added. In order to better understand how the findings translate to BBV152's effectiveness against Delta and other variants, and effectiveness against severe Covid-19 infection, more research is needed, she stated.

The assessment of vaccine effectiveness in a real-world setting, after being authorised or licensed, is an essential part of a vaccine roll-out plan. This is because the real-world performance can often differ from controlled trial conditions. The authors acknowledged the fact that the vaccine effectiveness in the study is lower than the efficacy observed during the interim analysis of the phase III randomised controlled trials, wherein it was found to be 77.8 per cent effective against symptomatic Covid-19 after two doses, according to the Lancet statement.

Factors Responsible For The Lower Vaccine Efficacy

Several factors may be responsible for the lower vaccine effectiveness, the authors noted. Firstly, only hospital employees were included in the study population. These participants have a higher risk of exposure to Covid-19 infection than the general population.

Secondly, there were high test positivity rates for both hospital employees and residents of Delhi, as the study was conducted during the peak of India's second Covid-19 wave. 

Thirdly, the authors attributed BBV152's lower effectiveness to the prevalence of circulating variants of concern, especially Delta variant.

Limitations Of The Study

Vaccine effectiveness against hospitalisation, severe disease, and death, which require further assessment, were not estimated in the study, the authors noted. Also, the study was not designed to estimate vaccine effectiveness for different time intervals after vaccination, or to determine if vaccine effectiveness wanes over time. 

Data on comorbidities and prior Covid-19 infection was absent. 

Also, the RT-PCR positive patients were not tested for SARS-CoV-2 variants, which means the type of variant that caused the infection was not known for any participant. As a result, the authors could not definitively estimate the vaccine effectiveness against symptomatic Covid-19 due to a specific variant, mentions the statement. 

The Delta variant's escape potential must be examined in future studies, the authors noted.

Professor Naveet Wig, Head of Medicine at AIIMS, said the study took place when the Covid-19 test positivity rate in Delhi was around 35 per cent, which is the highest since the beginning of the pandemic. He added this is an important to consider while interpreting the impact of a vaccine, mentions the statement.