FAQ: Why do I need the second shot of COVID-19 vaccine? Isn’t one enough?

While the first shot of the vaccine primes the body’s immune system to protect against the novel coronavirus, it may not induce a strong enough immune response.
A woman getting a vaccine
A woman getting a vaccine
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India is now vaccinating citizens above 18 years of age, who will get one of the shots out of the three approved vaccines – Bharat Biotech’s Covaxin, Oxford-AstraZeneca’s Covishield (manufactured in India by Serum Institute of India), and the Russian vaccine Sputnik V (distributed in India by Dr Reddy’s Labs). All of these require people to take a two-dose course. While the two doses of Covaxin should be taken 28 days apart, the second dose of Covishield should be taken 12-16 weeks after the first, and the second dose of Sputnik V, 21-90 days after the first shot.

Why is it necessary to take two doses? What happens if you only take one or miss the second? According to experts, a single dose of the vaccine does not produce strong enough immunity, which creates a requirement for a booster second shot. What the first dose does is that it primes the body’s immune system, getting it ready to fight against the novel coronavirus. “To be more specific, if the first dose may induce good immunity in a certain percent of people – say 30% -- for the rest of them, what it does is priming,” Dr John Jacob, a noted virologist, had told TNM. Over time, the non-replicating, weakened virus in the vaccine will get degraded into the body’s physiology.

So, you develop a partial immunity with the first dose, which, if not boosted, will wane over time, leaving you vulnerable again. However, this is not to say that priming is entirely forgotten by the body. Doctors have noticed that even those who have taken one shot get less severe disease if they contract COVID-19 when compared to those who are unvaccinated.

The second shot of the COVID-19 vaccine therefore, ensures that the immunity against COVID-19 stays for a longer period of time. “Your protection starts around two weeks after the first shot. It slowly increases over six weeks. Then it slowly starts going down. The second shot, taken by around 6-12 weeks, will augment the response and will keep you immune for longer. If you don’t take the second shot, your immunity will slowly start going down,” said Dr Vijayalakshmi B, Senior Consultant Infectious Diseases, Kauvery Hospital, Chennai, to TNM in a Facebook live.

There isn’t enough research yet to show how much protection the first dose of the COVID-19 vaccine alone can provide. On the other hand, both Covishield and Covaxin makers say that their clinical trials show 100% protection against severe disease if both doses of the respective vaccines are taken. Therefore, it is not advisable to skip the second dose.

Regardless of whether you have taken just the first shot or have taken both doses and are fully vaccinated, do not stop wearing a well-fitted mask, practising hand hygiene and maintaining physical distance. A vaccine does not provide 100% protection from getting COVID-19 altogether. It is very likely to protect you from severe disease, and ensure that you have a mild infection if you do contract COVID-19.

Watch: What happens if you miss the second dose of the COVID-19 vaccine.

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