Covaxin is 77.8% effective against symptomatic Covid: reading interim trial data

Covaxin, or BBV152, is an inactivated whole virion vaccine formulated with a novel adjuvant and administered in a two-dose regimen, 28 days apart.

Antibody response was found robust; no vaccine-related adverse events or deaths were recorded in the trial. (Express Photo: Partha Paul)

Interim data from a phase 3 trial of the Covid-19 vaccine Covaxin, developed in India by Bharat Biotech, show that two doses offer 77.8% protection against symptomatic Covid. The findings have been published in The Lancet. It comes days after Covaxin received emergency use approval from the World Health Organization (WHO) for people aged 18 and older.

Covaxin, or BBV152, is an inactivated whole virion vaccine formulated with a novel adjuvant and administered in a two-dose regimen, 28 days apart.

The trial & findings

The study was funded by Bharat Biotech International Limited and the Indian Council of Medical Research (ICMR). The trial took place between November 16, 2020 and May 17, 2021. It included 25,798 adult participants, of whom 24,419 adults were randomly assigned to receive two doses of the vaccine (12,221) or a placebo (12,198). The participants received the doses in 25 hospitals across the country.

The efficacy analysis was based on 130 symptomatic Covid-19 cases among 16,973 participants who were initially seronegative. These cases were recorded at least two weeks after participants had received a second dose.

There were 24 positive cases in the vaccine group (8,471 people) and 106 in the placebo group of 8,502, suggesting an overall efficacy of 77.8%.

Among the positive cases, there were a total of 16 cases of severe symptomatic Covid-19 disease. These included one in the vaccine group and 15 in the placebo group.

The findings indicate that Covaxin induces a robust antibody response, the paper said. No severe vaccine-related adverse events or deaths were reported among the trial participants. The majority of the adverse events, including headache, fatigue, fever, and pain at the injection site, were mild and occurred within seven days of vaccination.

Story continues below this ad

Also read | Molnupiravir and Paxlovid: Two new oral drugs and the treatment of Covid-19

Covishield & its efficacy

Covaxin is one of three vaccines being administered in India, alongside Covishield and Sputnik V (which constitutes a very small fraction of the total doses given). Covishield, from the Serum Institute is a version of the Oxford-AstraZeneca vaccine, or ChAdOx1 nCoV-19.

In data for the Oxford-AstraZeneca vaccine published in The Lancet in December 2020 and updated in March 2021, the vaccine showed varied efficacy depending on the strength of the doses and the interval between them. The updated analysis showed vaccine efficacy of 81.3% against symptomatic Covid when two standard doses were given 12 weeks apart.

Covaxin & Delta

In the Covaxin study, researchers conducted a preliminary analysis of efficacy against the Delta variant and found the vaccine to be 65% effective against symptomatic Covid-19 infection from this delta variant. They noted, however, that this data should be presented as preliminary and further observations are necessary to confirm clinical efficacy against Delta and other variants.

Also in Explained | New research: An oral version of remdesivir

Limitations

The authors of the Covaxin study have noted that the data are preliminary, and more research with a larger sample size is needed.

Story continues below this ad

They cited several limitations. Due to the low number of cases reported between the first and second vaccine doses, the researchers could not calculate vaccine efficacy after a single dose.

The data on efficacy against variants other than Alpha and Delta must be considered preliminary; the numbers reported are small, they said.

The study population was limited to India and therefore lacked ethnic and racial diversity, underscoring the importance of evaluating the efficacy of the vaccine in other populations.

Some groups, including pregnant women, and those living with HIV or with severe comorbidities, were excluded by the study inclusion/exclusion criteria.

Story continues below this ad

Newsletter | Click to get the day’s best explainers in your inbox

Anuradha Mascarenhas

Anuradha Mascarenhas is a Senior Editor at The Indian Express, based in Pune. With a career spanning three decades, she is one of the most respected voices in Indian journalism regarding healthcare, science and environment and research developments. She also takes a keen interest in covering women's issues . Professional Background Education: A gold medalist in Communication and Journalism from Savitribai Phule Pune University and a Master’s degree in Literature. Author: She authored the biography At The Wheel Of Research, which chronicles the life and work of Dr. Soumya Swaminathan, the former Chief Scientist at the WHO. Key Focus: She combines scientific accuracy with storytelling, translating complex medical research into compelling public and human-interest narratives. Awards and Recognition Anuradha has won several awards including the Press Council of India's national award for excellence in journalism under the gender based reporting category in 2019 and the Laadli Media award (gender sensitivity -2024). A recipient of the Lokmat journalism award (gender category-2022), she was also shortlisted for the RedInk awards for excellence in journalism-2021. Her debut book At The Wheel Of Research, an exclusive biography of Dr Soumya Swaminathan the inaugural chief scientist of World Health Organisation was also nominated in the Popular Choice Category of JK Paper AUTHER awards. She has also secured competitive fellowships including the Laadli Media Fellowship (2022), the Survivors Against TB – New Research in TB Media Fellowship (2023) and is part of the prestigious 2025 India Cohort of the WomenLift Health Leadership Journey.” Recent Notable Articles (Late 2025) 1. Cancer & Specialized Medical Care "Tata Memorial finds way to kill drug-resistant cancer cells" (Nov 26, 2025): Reporting on a breakthrough for triple-negative breast cancer, one of the most aggressive forms of the disease. Discipline, diet and purpose; How a 97-year-old professor defies ageing'' (Nov 15, 2025) Report about Prof Gururaj Mutalik, the first Head of Department at Pune's B J Government Medical College who at 97 credits his longevity to healthy habits and a strong sense of purpose. 2. Environmental Health (The "Breathless Pune" Series) Long-term exposure even to 'moderate' air leads to chronic heart, lung, kidney issues" (Nov 26, 2025): Part of an investigative series highlighting that even "safe" pollution levels are damaging to vital organs. "For every 10 µg/m3 increase in PM2.5 level, there was 6-8% jump in medicine sales" (Nov 23, 2025): Using commercial data to prove the direct link between air quality and respiratory illnesses in Pune. 3. Lifestyle & Wellness News "They didn't let cancer, diabetes and heart disease stop them from travelling" (Dec 22, 2025): A collaborative piece featuring survivors who share practical tips for traveling with chronic conditions. At 17, his BP shot up to 200/120 mmHG; Lancet study flags why child and teen hypertension doubled between 2000 and 2020'' (Nov 12,2025)--A report that focusses on 17-year-old-boy's hypertensive crisis and reflects the rising global trend of high blood pressure among children and adolescents. 4. Scientific Recognition & Infrastructure For promoting sci-comm, gender diversity: IUCAA woman prof highlighted in Nature" (Nov 25, 2025): Covering the global recognition of Indian women scientists in gender studies and physics. Pune researchers find a spiral galaxy like the Milky Way from early universe'' (December 3, 2025)- A report on how Indian researchers discovered a massive galaxy that existed when the universe was just 1.5 billion years old , one of the earliest to have been observed so far. Signature Beat: Health, Science & Women in Leadership Anuradha is known for her COVID-19 reportage, where she was one of the first journalists to provide detailed insights into the Covishield and Covaxin trials. She has a dedicated interest in gender diversity in health and science, often profiling women researchers who are breaking the "leaky pipeline" in STEM fields. Her writing style is scrupulous, often featuring interviews with top-tier scientists and health experts from various institutions. ... Read More