Bharat Bio's COVAXIN: Ten takeaways from successful animal trials of the experimental COVID-19 vaccine

The animal trials demonstrate that COVAXIN protected against SARS-CoV-2, and amped up two kinds of antibodies needed for a strong immune response against the virus.


Indian vaccine maker Bharat Biotech recently shared the results of their COVID-19 vaccine candidate safety trials in animals. The experimental shot, called 'COVAXIN', was found safe in rhesus monkeys that were vaccinated and exposed to the SARS-CoV-2.

The Drugs Controller General of India (DCGI), India's regulatory agency, granted approval for Phase I and II trials of the vaccine in June. Bharat Biotech, in a partnership with the National Institute of Virology, has concluded phase 1 human trials of their COVAXIN candidate at most of the 12 chosen centres as of 14 August. The results from the preliminary trial suggests that the vaccine is safe, principal investigators conducting the trials told the Economic Times. The second phase of human trials for the vaccine are likely to begin in the first week of September, as per the report.

Developed with the Indian Council of Medical Research (ICMR) and National Institute of Virology (NIV), Covaxin is an inactivated vaccine candidate. The inactivated vaccine is designed to produce unique elements of the SARS-CoV-2 virus, which are used by the immune system to recognize a threat if the whole virus in ever encountered in the real world.

An illustration of the two-dose vaccine regimen for COVAXIN that was tested in macaques. Image: Bharat Bio

An illustration of the two-dose vaccine regimen for COVAXIN that was tested in macaques. Image: Bharat Bio

Here are ten things we learned about the COVAXIN animal trials.

  1. Safety and protection against SARS-CoV-2 tested in monkeys. The animal trial (part of Phase I) was a test of how safe (three different formulations of) the inactivated COVID-19 vaccine was in rhesus macaques. Also measured was the shot's ability to offer protection against exposure to the SARS-CoV-2 virus.
  2. Robust immune response was produced. The experimental COVAXIN shots reportedly prompted "robust" immune responses in monkeys. It worked in preventing SARS-CoV-2 infection and COVID-19 in all the monkeys given the vaccine. The vaccinated monkeys didn't fall ill with COVID-19 even when exposed to high levels of live SARS-CoV-2 virus in an artificial challenge.
  3. Live virus challenge in monkeys. The vaccine was tested in 20 rhesus macaques, who were divided into 4 groups of 5 each. One group was given a placebo, while the other three groups were immunized with 3 different vaccine candidates at day 0 and day 14. Fourteen days after the macaques were given the second shot, scientists challenged them with live SARS-CoV-2 virus.
  4. Two-dose regimen. COVAXIN is intended as a 2-dose vaccination, and was tested in monkeys at two different concentrations – 3 µg and 6 µg doses, along with an adjuvant that enhances immune response. This regimen produced a "significant immune response" and offered protection against the SARS-CoV-2 virus, experts said in the trial report.
  5. Two kinds of protective antibodies. The results from animal trial show that COVAXIN protected monkeys against the SARS-CoV-2 virus. There was an increase in two kinds of antibodies needed for a strong immune response – anitbodies that can neutralize SARS-CoV-2 virus, and an important class of antibodies used to fight infection (SARS-CoV-2-specific IgG). This indicates that the experimental vaccine could similarly bring down the amount of virus replicating in the respiratory tract and organs like the nasal cavity, throat, and lung tissues.
  6. Protection kicks in 3 weeks after vaccination. The protective response of COVAXIN seems to be much better in the third week of immunization, as per the report. This was when the levels of SARS-CoV-2-specific IgG and neutralizing antibodies were considerably higher than other time points in the trial.
  7. No pneumonia after virus challenge. There was no evidence of pneumonia in the vaccinated macaques. Pneumonia has proven to be a key indicator in severe COVID-19 cases. When the placebo group was challenged with the SARS-CoV-2 virus, the monkeys showed interstitial pneumonia and virus particles in the lung tissue, showing that the infection continued.
  8. Adverse events. The trial report claims that no adverse effects were seen in the animals with the two-dose vaccination regimen, which is an encouraging finding for the ongoing human safety trials.
  9. Phase I human trials still underway. The information collected from the Phase I study substantiate the immunogenicity of the vaccine candidates and BBV152 is being evaluated in Phase I clinical trials in India (NCT04471519). The Phase I study involves 375 volunteers at 12 sites across the country, including PGI and All India Institute of Medical Sciences (AIIMS), Delhi. It is expected to be completed by the end of this month.
  10. Report is under peer-review. The study has been pre-published in Nature Research, and is still awaiting peer-review.

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