“In the long term, if effective and safe, such a strategy could help countries manage supply constraints, while providing flexibility in vaccination programmes. It is also possible that combinations have an advantage in stimulating immune responses, but this can only be confirmed through research studies,” Swaminathan told TOI.
Two studies recently demonstrated that the AstraZeneca vaccine followed by the Biontech/Pfizer as the second dose resulted in high levels of neutralizing antibodies. “There are studies going on. We need to wait for those, but at the moment we only have data on the Oxford AstraZeneca vaccine followed by Biontech/Pfizer, which is encouraging. We need both safety and immunogenicity data on different combinations” she said.
India is yet to start any studies in this regard, officials from the Indian Council of Medical Research (ICMR) said. “As of now, we are not carrying any such studies. However, we may explore it in the near future,” senior epidemiologist Dr Samiran Panda said.
Eminent virologist T Jacob John also agreed with Dr Swaminathan. “Studies have to be done to explore this option. If it helps in eliciting greater immune response, it can help in addressing shortage of vaccines too,” he said.
On the Emergency Use Listing for Covaxin, the WHO chief scientist said the organisation was expected to take a decision in this regard in four to six weeks as an independent technical assessment panel was evaluating the proposal and the submitted data.
With many countries discussing booster doses, she said there was a need to prioritise doses for countries where healthcare and frontline workers, as well as the elderly and the vulnerable, are yet to receive their first dose.
“If countries start administering the booster shots, this would require a huge number of doses. Moreover, there is no scientific evidence to suggest that boosters are definitely needed. What we have observed is persistence of immune responses in the majority of vaccinated individuals for at least 8-9 months. Whether a certain group of people will eventually need boosters is something we need to understand through cohort follow up studies,” she said.
She said the need for boosters may also differ by vaccine type since they are made using different technologies.