With experts talking about the need for booster doses and the benefits of mix-and-match vaccines, Metrolife sought to know the opinion of Bengaluru doctors.
A leading virologist recommends booster shots for those above 60 and patients under treatment for cancer and organ transplant.
Dr T Jacob John, (retd) professor of clinical virology, Christian Medical College, says booster shots are necessary for men above 65 years, obese people, those with diabetes and those undergoing immuno-suppression treatment because of cancer and organ transplant.
These categories, he says, will need a booster shot to keep the immunity up. “While some women have better immune responses than men. Booster shots increase the height and breadth of immunity with the new variants also being covered,” explains Dr John.
Dr Uma Chandra Mouli Natchu, associate professor, infectious diseases, St John’s Research Institute, says vaccine protection starts with the human immune system’s ability to recognise the virus.
“When mutations cause new variants with altered shape or form of the spike protein, protection is usually reasonable as long the new spike protein and the virus can still be recognised and neutralised by the immune system. Current vaccines do a reasonable job of protecting against new variants currently in circulation,” he explains.
He feels vaccinating people rapidly is the best way to reduce the occurrence of new variants.
“Unless we have evidence that the virus has become sufficiently unrecognisable, we should continue to use existing vaccines. Meanwhile, work on vaccines against newer variants is ongoing, and the advantage with mRNA vaccines and adenovirus vector vaccines is that the genetic material that codes for the spike protein can be quickly replaced with the code for the new variant protein,” he says.
Dr T Jacob explains that most vaccines are based on inactivated viruses like those used for Hepatitis A and B. Some childhood vaccines, like DPT, come in three doses.
“The immunity achieved by two doses is good enough to protect you from an ICU admission, but you may still get moderate disease and if the immunity is low you may get serious diseases,” adds Dr Jacob.
He feels booster doses should be given four to six months after the first two shots for long-lasting protection. “But for immediate results, because we are in the middle of a pandemic, the third dose should be given within six weeks,” he adds.
Fast mutations
Dr Vishal Rao, dean of academic research at a cancer centre and member of the government’s Covid task force, says India alone has seen 8,572 escape mutations, among the 25,000 total.
“A lot of companies have gone back to the drawing board to figure out if they have to work on a new vaccine or whether a booster shot will do against the genomic variants. Both these plans are being discussed,” he told Metrolife.
He says it is not advisable to mix vaccines without understanding the reactions. The community of virologists and immunologists is not discussing boosters and mixed doses because they don’t want to trigger panic, he says.
Premature talk
Dr Chandra Mouli says the use of two vaccines against the same illness, with different strategies, is not new to vaccinology. For instance, children get both the Injectable Polio Vaccine (IPV – an inactivated vaccine-like Covaxin) and the Oral Polio Vaccine (OPV – an attenuated oral vaccine which is like Covishield) as part of vaccination guidelines.
“When some European countries decided to stop using the AstraZeneca vaccine (called Covishield in India) due to the small risk of clots, people who had received the AstraZeneca vaccine were given the Pfizer mRNA vaccine as the second dose,” he says, adding that side effects following vaccinations in Germany seem to be lower in the group that received this combination along with higher levels of antibodies.
The Sputnik vaccine, he says, has been designed as a heterologous pair of doses, the first dose uses one adenovirus strain and the second a different adenovirus strain. The idea is to keep them immunologically different to generate a better boost.
“So we already have evidence that mixing vaccines can work. A word of caution is that some combinations may not work as well as others and it would be prudent to collect information on everyone who accidentally or due to lack of availability ended up taking mixed vaccines. As of now, the AstraZeneca vaccine followed by an mRNA vaccine and different adenovirus vector vaccines seem to work,” he says.
WHO says
World Health Organization’s chief scientist Soumya Swaminathan says there is no concrete evidence yet to recommend booster doses.
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