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Explained | How far can people delay taking the second shot of COVID-19 vaccine?

Recipients wait in long queues outside the BKC jumbo vaccination centre at Bandra Kurla Complex in Mumbai on April 24, 2021.   | Photo Credit: EMMANUAL YOGINI

The story so far: Despite a massive shortage of COVID-19 vaccines across the country, the Central government announced that vaccination for everyone above 18 would begin from May 1. But several State governments expressed their inability to kick off the programme citing a shortage of vaccines. They have postponed the drive to when the required stocks arrive in each State. This could have a deep impact on the epidemiological health of a population seized by a deadly second wave of infections.

What is the extent of the shortage?

India is currently producing roughly 2 million vaccines a day, and according to data on the Co-WIN portal, the number of vaccines being administered daily is roughly 2.3 million to 2.5 million. The shortage is stark. Technically, the production capacity falls below even the daily requirement.


As of April 29, 9.1 % of the population had received one dose of the vaccine, and only 1.9 % had been “fully vaccinated”. That leaves out a huge share of the population that is still not inoculated.

Chandrakanth Lahariya, vaccinologist and epidemiologist, says the maths behind it is incontrovertible. “Even at the current production levels, the demand is higher. The vaccination has been opened to the additional population and the demand has increased three-fold, while supply remains the same.”

He reasons that even with other manufacturers being allowed to produce vaccines and a few million doses of the Russian vaccine Sputnik expected shortly, increasing production will take time. The Serum Insititute of India, the maker of Covishield, looks to scale up production to 100 million doses per month soon, and Bharat Biotech, which manufactures Covaxin, is talking of producing 50-60 million doses a month. But even in the next few months, the production is unlikely to go far beyond 150 million doses a month.

Can people prolong the interval for their second dose?

Both vaccines available in India have a two-dose schedule. For Covishield, the AstraZeneca vaccine, T. Jacob John, renowned virologist, formerly with Christian Medical College, Vellore, said, “Phase 3 trials were conducted across many countries with varying intervals. They figured that a second dose 12 weeks later offered the best protection. Studies with a six to eight-week interval also found a linear relationship, with efficacy improving over time.” In times of no urgency, the best option is to take the second shot at 12 weeks, but in the face of the second wave, however, he cautions that patients should take the vaccine on time to reduce the risk to themselves.

The second dose of Covaxin can be taken four to six weeks after the first.

Also read | Can people test positive for COVID-19 even after inoculation?

Dr. Lahariya says that India should increase the gap for Covishield to 12 weeks. Any immunisation schedule is based on technical and operational feasibility, he says. In routine immunisation for children, most vaccines are administered at a four-week gap in India, while in many countries abroad, they are given after an eight-week gap. “Here, the operational reason is that coverage is already low. If we increase the vaccine gap, it might unnecessarily delay vaccination, especially for DPT. So, we have to design our vaccination programme based on scientific evidence and operational needs.” In Covishield, the higher the gap, the greater is the proven efficacy. And several million doses will be saved to allow people to take at least one shot.

However, this scenario cannot be extrapolated for Covaxin, adds Dr. Lahariya. At this point, the advice would be to encourage people to get doses whenever they can. “Irrespective of when the second dose is taken, it counts,” he says.

Immunologically, it is understood that when a person has been given a vaccine (even one dose), the immune system is activated. This means the system can mount a better response than a naive immune system in someone who is not vaccinated, says Dr. Lahariya.

If a person contracts COVID-19 after the first dose, when should they get the next shot?

Dr. Lahariya says according to the broader principle, it is appropriate to delay vaccination. “Natural infection provides some protection for a few months. If a person has already received one shot within a month, then the natural infection becomes some sort of a booster infection. Given the operational challenges, delaying the second shot can be done fairly confidently. However, the decision should be left to people.”

Dr. John points to the evolving guidelines released by the United States’s Centers for Disease Control and Prevention (CDC). “Originally, CDC came up with a three-month gap, and later changed it to a one-month gap, and finally, we have, I think, an advisory to take it any time after full recovery, or after the person becomes completely asymptomatic.”

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Printable version | Jun 17, 2021 2:47:49 AM | https://www.thehindu.com/sci-tech/health/explained-how-far-can-people-delay-taking-the-second-shot-of-covid-19-vaccine/article34461062.ece

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