People who have received the first dose of Covid-19 vaccine need not restart their vaccination schedule if the gap between the prime and the booster shot goes beyond the stipulated 4-6 week interval, according to a top health official. As the country faces a shortage of vaccines, there has been a rising concern among the first dose recipients that the delay in getting the booster shot might leave the prime dose ineffective. However, according to experts, that is not the case and recipients need not worry.
“We know there are many single-dosers whose second shots have been delayed. They need not worry. Even if the gap between two doses increases to 8-10 weeks, in case of any of the two vaccines (Covishield and Covaxin), beneficiaries can take the second shot and it will still be effective. There is not need to repeat the vaccine schedule due to delayed second dose," a TOI report quoted Dr NK Arora, member of the National Committee on Adverse Events Following Immunisation.
Immunologist Dr Vineeta Bal from the Indian Institute of Science Education and Research (IISER) Pune explained that the immune response triggered by the first dose does not disappear because of delay in taking second dose, just that it’s not optimum. “A booster dose essentially increases the quality and quantity of the first dose response," she told the newspaper.
Adding a word of caution, Bal suggested the elderly people to avoid crowded vaccination centres as they might contract the infection there.
Although the prime dose remains in the body, it has its own limited half-life. All antibodies get degraded within the body and so, the immune respose generated by the first jab may start tapering after 4-5 months.
During the international trials of Covishield, it was found that the vaccine remains effective even when the second dose is administered as late as after 12 weeks. Covaxin was not tested for such a variation of duration between the two doses in human beings. “The makers had uniformly tested at the end of four weeks. That’s why everybody is recommending booster for Covaxin at the end of 28 days. Theoretically, if there is enough response that lasted for 4 week, maybe it will last up to 5 weeks too. But we don’t know that since there is no data," said Bal.
Those, who contract COVID-19 even after getting the first jab and take 6-10 weeks to recover, should still take the second dose and complete the vaccination schedule.
Meanwhile, Dr Naveen Thacker, executive director of the Internationa Pediatric Association and a member of the Gujarat Covid task force told TOI, “Irrespective of the vaccine, it is always better to have a slightly longer gap in most case. In case of Covaxin, the data published so far suggests a minimum interval of 4-6 weeks, but perhaps a longer gap could be more effective. Either way, those due for their second shots must take it even if it’s delayed."
He also stated that people don’t need to get their first dose again if the follow-up is delayed. The same viewpoint was voiced by Dr Subhash Salunke, advisor to the state on Covd control.