Mcb777 Casino Why scientists think we will need booster shots for Covid

On December 8, 2020, Margaret Keenan, 90, became the first person to receive a Covid-19 vaccine. Since then, more than 1.7 billion doses have been administered across the world.Six months on, one issue receiving serious attention is: how long can the approved vaccines remain effective, and will we need booster shots? The answer will depend on how our immune system responds in the long run and how the virus transforms (new variants). But for now, there appears to be a growing consensus that boosters will be needed.Immunity responseB cells, a type of white blood cell in our immune system, have receptors that bind to pathogens. With the help of T cells, another part of our immune system, they produce antibodies allowing macrophages – the immune system’s first line of defence – to destroy the pathogen. A vaccine induces such a response.Senior microbiologist Prof Vijaya S from the microbiology and cell biology department of IISc, told TOI: “Some subunits of ‘memory’ B and T cells stay around, remember and reactivate the immune system if the same virus invades again.”She explained that in some cases – like in rubella – the ability to reactivate the system lasts long, but in some it does not. If the system does not have this ability against a particular pathogen after vaccination, it’ll need boosters. “But we have found nothing conclusive on SARS-CoV2,” she said.Untitled Carousel 83300531Preparing for boostersLast month, Pfizer CEO Albert Bourla said people will “likely” need a booster dose of a Covid-19 vaccine within 12 months of full vaccination. A few weeks prior to that, Bharat Biotech got permission to test the third – booster – Covaxin dose in India.Does this mean we need it? “Yes,” says veteran virologist Dr T Jacob John. “The expectation is that we’ll need a booster, but whether we’ll need a yearly dose or one dose in the first year and that’s all is unpredictable because the pandemic is only one year old.”There’s still no clarity on whether immunity after vaccination may extend beyond 11 months, as Dr Len Horovitz, pulmonary specialist at Lenox Hill Hospital in New York, put it in one interview. No long-term immunity means we cannot rely on previous infection (memory) to achieve immunity the way we could with measles or mumps. medium nocaption83363740 Variants’ impactGrace Lee, infectious diseases physician at Stanford Children’s Health, told The New York Times variants are inevitable. “I think the question is, how impactful are they going to be?”John says while we knew from the beginning Covid-19 would be endemic and people would need vaccines, newer variants triggered studies on whether existing vaccines are effective.According to Nature, initial lab tests suggested antibodies raised by the Pfizer-BioNTech vaccine were less effective against the B.1.351 variant. However, in May, researchers in Qatar published reassuring data showing people who received two doses were 75% less likely to develop Covid-19 from B.1.351, and almost completely protected from severe disease.Another variant of concern – B.1.617.2 – raises worries of being unusually transmissible. Public Health England has determined that two doses of Pfizer-BioNTech and Oxford-AstraZeneca vaccines are 88% and 60% effective, respectively, at preventing symptomatic disease caused by this variant.If the efficacy is proven to reduce with newer variants, boosters become inevitable. medium nocaption83363288How third dose worksSo far, John says, evidence shows variants dominate mainly because they transmit better and not because of ‘vaccine escape’ (when completely new strains originate).That’s why vaccine makers have claimed some efficacy against newer variants. This means there may not be a need to create new vaccines, and boosters will be enough.John, who has himself taken a third dose of Covaxin and sent the serum for testing, explains this: higher immune responses are needed to broaden the cross reactive protection against variants. If you hyper-immunise your immunity more than the recommended two-dose schedule, the ability to tackle related antigens (variants) becomes high. This is being tested.“The principle is that if you boost it very high, it has two advantages: One, it will be longer-lasting. Two, like an umbrella, if you stretch it more the more coverage it gets.”Also, as has been reported over the past few weeks, countries are looking for data to support mix-and-match of vaccines. If vaccine cocktails prove to be efficient, a different vaccine can be used for additional boosters. After all, the second dose of existing vaccines is a booster. In the US, a trial is on to use Moderna on those who’ve taken the Pfizer-BioNTech vaccine.Untitled Carousel 83166489