Will India go for mixing vaccines for booster shot? Decision soon

A third shot that does not match the first two doses may be allowed

The decision on whether to all­ow heterologous boosting — or a different vaccine for the third shot — in India is expected soon. Investigators from Christ­ian Medical College, Vellore, who have been carrying out a cl­inical study on mixing vaccin­­es, are likely to present their int­erim data from 400 volunteers.

Multiple sources confirmed that a presentation before the subject expert committee of the Central Drugs Standards Con­t­rol Organisation (CDSCO) is ex­p­ected this week. “We have sou­g­ht permission from the Drugs Co­ntroller General of India (DCGI) to present the data be­fo­re the experts,” said Winsley Rose, principal investigator of the study, adding that the interim data was ready. Rose, however, did not divulge the results of the study, which tested if heterologous boosting gives beneficial results.

A senior government official said that the DCGI is also likely to take a call on whether any va­c­cine would be allowed as a boo­ster shot. Sputnik Light and na­sal Covid vaccines from Bha­rat Biotech have already sought pe­rmission to be used as boosters. “Bharat Biotech has sought app­roval for using the nasal vaccine both as a preliminary dose and also as a booster after one has received two doses of any Co­vid-19 vaccine,” said the official.

“So far studies conducted globally, and also locally, have shown that heterologous boosting, or mixing vaccines, gives good results. We are awaiting details from the CMC study, based on which a final call will be taken,” the official added. When and for which age group the third vaccine dose will be allowed is a decision that the National Immunization Tech­nical Advisory Group (NTAGI) will take, the official added.

The DCGI had approved the CMC, Vellore, study on mixing vaccines in July last year. The study has tested 200 volunteers who got two doses of Covishield and 200 who were fully vaccinated with Covaxin. “Of these, 100 of those who got two Covishield doses were given Covaxin as the third shot. The remaining 100 were given Covishield as the third shot. The same was done for volunteers fully vaccinated with Covaxin,” Rose explained.

“There would be significant advantages to having flexible immunisation programmes where the second vaccine dose is not necessarily the same as the first dose, and the intervals between the doses are similar. Accordingly, this study will determine the safety as well as the immune responses to mixed administration of Covishield following Covaxin and vice-versa given at an interval of 56 +/- 7 days and make comparisons with the same two-dose administration of these two vaccines,” according to the Clinical Trials Registry of India’s (CTRI’s) summary of the study.

Last October, the Indian Co­u­ncil of Medical Research had said that a limited study conducted among 18 participants had found that a combination of Covishield and Covaxin shots is not only safe but also offers better immunogenicity (ability of cells/tissues to provoke an immune response) than two doses of the same vaccine.

The researchers, however, had said the evidence was limited and called for multi-centre randomised clinical trials to conclusively prove the findings.