Pharmaceutical company Bharat Biotech’s coronavirus vaccine, Covaxin, was on Monday declared “safe” and “immunogenic with no serious side effects”, according to a study published in The Lancet medical journal on its second phase results. This came a week after Bharat Biotech announced that the homegrown vaccine has shown 81% efficacy in the third phase of clinical trials.

Covaxin, developed in collaboration with the Indian Council of Medical Research and the National Institute of Virology, is one of the two vaccines approved for emergency use in India.

The study found that Bharat Biotech’s vaccine showed “better reactogenicity and safety outcomes, and enhanced humoral and cell-mediated immune responses” in comparison to phase one trial. It, however, added that the second phase results reported do not permit efficacy assessments and further corroboration with third phase outcome was required.

The Lancet publication said:

“The evaluation of safety outcomes requires extensive phase 3 clinical trials. We were unable to assess other immune responses (ie, binding antibody and cell-mediated responses) in convalescent serum samples due to the low quantity. Furthermore, no additional data on the age of the participant or the severity of disease from symptomatic individuals were obtained. Comparisons between phase 1 and 2 trials were not done in a randomised set of participants, and no adjustments on baseline parameters were made. Conclusions are to be considered as post-hoc analyses.”

It noted that the vaccine induced “high neutralising antibody responses” which were “elevated in all participants” at three months after the second inoculation. It said the proportion of participants reporting adverse events in the second phase trials was also lower than those in first.

“Longitudinal follow-up of additional post-vaccination visits (at months 3, 6, and 12) is important for understanding the durability of immune responses, and is ongoing,” The Lancet study said.

Faheem Younus, Chief of Infectious Diseases at the University of Maryland Upper Chesapeake Health, US, called the development “good news”.

Covaxin had earlier raised concerns among experts as the Central Drugs and Standards Committee approved it for use before completing the third phase human trials. Health authorities, including ICMR chief Balram Bhargava and Union Health Minister Harsh Vardhan, have repeatedly said the shot is “safe and immunogenic”.