- The vaccine needs to be given in two doses
- It is important to get the second dose of vaccine
- The second dose should be from the same vaccine manufacturer
There are several vaccines being developed for COVID-19. Each of them is being given at slightly different dosing schedules. But what if you miss the second dosage? Explaining this Dr Soumya Swaminathan, Chief Scientist, World Health Organization (WHO). Most of the vaccines being developed need at least two doses, but there are some single dose vaccine candidates as well, she informs. The interval between the doses depends on which vaccine you're getting. The local authorities and the government will inform you about when the second dose is due.
Second dose of COVID-19 vaccine- What you should know
"Most of the two-dose vaccines currently are being given three to four weeks between the first and second dose. But, there is some data from some vaccines like the AstraZeneca vaccine, where delaying the second dose upto 12 weeks actually gives a better immune boost," says Dr Swaminathan in WHO's IGTV.
It is important to get the second dose of the vaccine, if the vaccine is a two-dose schedule, even if you delay it by a few days or weeks. "It doesn't matter if its early or late by a few days or even a couple of weeks. What's crucial is to go back and get that second dose because the first dose presents this antigen to the immune system to prime it. And the second dose is the one that really gives a boost to the immune system," she informs.
The second dose gives a boost to the immune system so that the antibody response, as well as T cell mediated response are strong. "They also develop a memory response, which then lasts for a long time, so that when the body sees this antigen again, or when it is exposed to the virus protein again, it knows that it needs to react quickly," Dr Swaminathan explains.
Can the two dose of vaccine be from different manufacturers?
There are now clinical trials ongoing in some countries, that are looking at interchangeability-the first dose with one vaccine and the second dose with a different vaccine, maybe even a different platform vaccine. "Immunologically, there are reasons why this would make sense. However, at the present time, there isn't enough data for us to recommend this type of interchangeable two dose schedules," she says.
Thus, for the time being, the policy advice from WHO recommends that you should have the second dose from the same vaccine manufacturer as you had in the first dose.
How has it been ensured that there are no long-term effects of the vaccine?
Usually, clinical trials of vaccine are done in tens of thousands of people, who are followed up for a couple of years to test its efficacy and safety. But because of the pandemic and the need to get the vaccines out quickly to save lives, the duration of follow up in the case of COVID-19 vaccine, has been a couple of months rather than years.
Emergency use authorisation have been given to these vaccines. This means that the vaccines are still under observation. Follow ups are being taken from people who have got the vaccine, for any serious or adverse effects.
"Over 150 million doses of vaccines have been administered around the world. So far, the safety signals have been reassuring. We will continue to watch this very carefully and if there is any evidence of relationship between a vaccine and a side effect, then that will be analysed and the guidance to the countries will be updated," Dr Swaminathan clarifies.
(Dr Soumya Swaminathan, Chief Scientist, WHO)
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