What happens if you miss second dose of Covid-19 vaccine?

The Centre has announced Phase 3 of the vaccination drive against the coronavirus under which all adults (18 and above) are eligible to get the jabs beginning May 1. However, various states have flagged the issue of shortage of vaccines, forcing them to shut down vaccination centres.

Over 11 crore Indians have received their first dose of the jab and many of them are due for their second one. While the government has maintained that there is no shortage of vaccines, palpable fear has emerged among the public who are now afraid that they may miss their appointments for their second dose.

Experts believe that in order to evade serious conditions from the coronavirus, one needs to be fully vaccinated.

Also read: Nagaland stops administering first dose of Covid vaccine due to shortage

India, as of now, has been administering two vaccines but the interval between the two doses differs for each. Covaxin, manufactured by Bharat Biotech, needs to be administered with a gap of 28 days.

As for Covishield, Serum Institute of India's brand of Astrazeneca-Oxford vaccine, needs to be taken with a gap of 4-8 weeks.

Recent studies say pushing the gap further to 12 weeks for the AstraZeneca vaccine does not affect the efficacy. Another British study has said, a single dose of the vaccine can reduce the infection rate by 65 per cent.

Also read: India's Covid-19 crisis imperils global vaccination efforts

However, the vaccine, by design, works only when both doses are administered. Virologist Dr. Jacob John told the Newsminute that a single dose does not offer protection. “It means that if you get exposed to the infection, you may get infected, get the disease, and even get it severely,” he said.

When the first dose is administered, the vaccine nudges the immune system to develop resistance against the virus, a process known as priming. The second dose, however, boosts the priming, offering substantial protection against the pathogen. "So if you miss the boosting, then you remain vulnerable because you have only been primed," the expert said.

Also read: India fastest in world to administer over 14 crore Covid-19 vaccine doses: Govt

Nevertheless, it is not impossible to get the infection even after the second dose. Government figures indicate over 5,000 fully vaccinated people were infected and the number stands over 20,000 for those who got the first dose. "This is a very small number and not at all worrisome," the Union Health Ministry had said.

But, missing the second dose can potentially be a serious concern.

“There is an immunological memory that is peculiar to the immune system, like the memory in your brain. It will last about a year. So the second dose booster can be delayed up to a year, and still the protection due to the second dose will be available after boosting. This memory may last more than a year too,” Dr Jacob said.

Dr. Aju Mathew, an epidemiologist, told the publication, "There is no data or evidence to give us actual estimates of the immunogenicity of one dose of vaccine after prolonged interval."

He said one can only "hypothesise" that a single dose of vaccine may not be as robust as a person who got both.

"But it would still be much better than someone who is unvaccinated," he said.