Centre’s decision on mix-and-match boosters likely in two weeks: Official

The government may be able to decide in two weeks whether to mix and match the booster doses of approved Covid-19 vaccines based on India-specific trial data being prepared by the Christian Medical College in Vellore, according to people familiar with the development.

CMC Vellore, which was permitted to conduct homologous as well as heterologous booster dose trial by the national drugs regulator last year, is soon going to generate adequate data to be able to present before the subject experts of Central Drug Standard Control Organisation (CDSCO).

“We got permission from the health ministry screening committee to test samples from the study late last week. Two weeks would be needed to generate data,” said Gagandeep Kang, senior vaccine expert and faculty at CMC Vellore, who is spearheading the study.

“The sample testing has begun and in a week or so we should be able to generate relevant data that will be submitted first to the data safety and monitoring board. Following their approval, we will present the data to CDSCO,” Kang said. “We have already sought an appointment from the drugs regulator on this,”

In July last year, the national drugs regulator permitted CMC Vellore to conduct the study, and in March, the preliminary findings were shared with national technical advisory group on immunization (NTAGI) for analysis.

NTAGI in its last meeting asked for more data on neutralizing antibodies, according to people familiar with the matter. The researchers again applied to the health ministry for approval to conduct further testing after generating additional funds for it.

“The data on IgG anti-spike antibodies was presented to NTAGI’s Covid19 Working Group by Dr. Winsley Rose. With health ministry screening committee permission, we will be able to measure antibodies to other parts of the virus and also surrogate neutralizing antibodies that measure the ability to reduce binding of the spike protein to the ACE2 receptor,” Kang said. “We will also be able to assess differences in surrogate neutralizing antibodies to different spike proteins of variants.”

The vaccines being tested are the primary dose of Covishield, and Covaxin as the booster dose, and vice versa, as both these vaccines have been largely administered under the national Covid-19 immunisation programme.

The data, if approved, will then be presented before NTAGI that is already looking at scientific evidence in favour of recommending mix and match booster dose against Covid-19 to the health ministry.

Even though the exact data is not in public domain yet, preliminary findings of the study seem to show better response when heterologous booster dose is given, according to people familiar with the matter.

The Indian Council of Medical Research’s National Institute of Pune (ICMR-NIV) also analysed safety and immunogenicity of the heterologous vaccination regimen of Covishield followed by Covaxin, and compared it with two other cohorts, receiving either two doses of homologous Covishield or Covaxin.

In May last year, 20 villagers in Uttar Pradesh accidentally received first dose of Covishield and second of Covaxin. ICMR-NIV followed 17 of them and found better response as compared to those who received homologous dose.

“We could follow-up 17 individuals in the second round at 6 months following administration of the second dose. Here, we report the findings of the IgG antibody responses against S1-RBD and the neutralizing antibody (NAb) titres of the heterologous and homologous vaccination regimes against the SARS-CoV-2 VOCs (Alpha, Beta and Delta) and its comparison with prototype B.1 at 1 and 6 months and with Omicron post-6 months,” said researchers in a paper published on the analysis in February.

“It is very clear from the geometric mean titre of the heterologous group at 1, 6 months and their ratio compared with homologous vaccination groups that the heterologous CS and CV vaccination is immunogenically superior to homologous vaccination,” they said.