From 9 January, India will open booster shots for front-line workers and those above the age of 60 with co-morbidities. Mint looks at the rationale behind the booster strategy for India and if these shots can help prevent a new wave of infection.
Why are boosters recommended?
Booster doses are a way to prime the immune system to fight against a pathogen after the initial vaccination. Booster doses are routinely administered to prevent diseases such as Polio, Rabies, Hepatitis, and common flu. Covid-19 vaccines were introduced almost a year ago. Data now shows that though vaccines prevent severe illness, their effectiveness in preventing covid-19 symptomatic infection reduces over time. Data from the US Centre for Disease Control shows that the antibodies wane from six to nine months after two doses of vaccination. With fears around long covid, boosters may help prevent infection.
Which population group needs them?
Though countries in the West have recommended boosters for all adult population, the evidence to use them is highly tilted towards the elderly population, those who are immunocompromised, and frontline workers. The World Health Organization has also recommended boosters for those jabbed with the inactivated virus vaccines (vaccine platforms by companies such as Sinovac, Bharat Biotech). For the immune-compromised and the elderly, the booster is a way to keep generating antibody response. Boosters for healthcare workers ensure their protection and thus lower the burden on the healthcare system.
Can one be infected even after the boosters?
We don’t know. There is no evidence yet whether boosters completely prevent infection. What they tend to do is make the symptomatic infection milder over time. Boosters could also become ineffective with the emergence of new coronavirus variants. The scientific community is of the view that SARS Cov2 vaccines could become a yearly affair.
What are the other countries doing?
While India has recommended boosters nine months after the second vaccination, the CDC recommends boosters six months after taking the two doses of the mRNA vaccines (Pfizer/Moderna) and two months after taking the one dose adenovirus vaccine (J&J). The UK recommends boosters after three months and Singapore after five months. Though India hasn’t clarified about the nine-month gap, there is some evidence that a longer interval between the first and second dose gives a stronger immune response.
Can vaccines be mixed for boosters?
Yes. Mixing of vaccine doses, also known as heterologous vaccination, is considered a better vaccination strategy from a scientific as well as logistical perspectives. Mixing doses of adenovirus vaccine with an mRNA vaccine can lead to longer resistance towards infection, studies show. India is in a unique position to test the benefits of heterologous vaccination as vaccine companies here are working on almost all platforms. Trials for mixing Covisheild and Covaxin are currently on.
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