ROUTINE vaccination of healthy children and teenagers against Covid is of little benefit to them and would not protect adults from the virus, according to a top infectious disease expert.

Eleanor Riley, professor of immunology and infectious disease at Edinburgh University, said such a policy would only make sense if it completely stopped the spread of the virus - something that is no longer possible with the Delta variant.

Speaking on the BBC Sunday Show, Prof Riley said: "It's quite clear now that the vaccines we have are very very good at preventing people ending up seriously ill in hospital with Covid, but they're not so good at preventing infection and transmission with the Delta variant of the virus.

"And so even if we vaccinated everybody in the country, the virus would continue to circulate albeit at lower levels that otherwise, so we have to be very clear about what we are trying to do.

"I think the argument that vaccinating children is to protect their teachers, their parents, their grandparents, I think we can probably put that to one side now because we know that even if the kids are vaccinated they are still potentially able to transmit the virus.

"If we want to protect people we have to protect them by vaccinating them but not by relying on somebody else to be vaccinated, so the question then is who really needs a vaccine and for children under the age of 16 the evidence is that not many of them are going to benefit hugely from being vaccinated in terms of getting sick with Covid. Some will, but many won't."

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Both the Pfizer and AstraZeneca vaccines cut the risk of being hospitalised with Covid by more than 90%, but they are less effective at preventing symptomatic infections caused by the Delta variant than they were against the previously dominant Alpha (Kent) strain.

In the case of the Pfizer vaccine, efficacy is around 83% against Delta compared to 92% for Alpha; for AstraZeneca it is estimated at 61% against Delta compared to 81% against Alpha.

Prof Riley added that it was also not yet clear who should be given booster jags despite the rollout being expected to get underway in September.

Although antibody levels in the blood fade months after vaccination, other elements of the immune system - such as T cells and memory cells - can still offer protection, and scientists do not know what threshold of antibody protection is needed to fight off the virus.

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Prof Riley said: "If you started off with 100 times more antibodies than you needed then if your antibodies drop by 50 per cent that probably doesn't make any material difference to whether you're going to get infected, pass the infection on to somebody else, or get sick. "We don't yet know what that level of antibody is that people need to maintain in order to remain protected and prevent them transmitting.

She added: "At some level we can take a completely pragmatic approach and say those people who are most at risk, who've always been most at risk, and who got their vaccines right at the beginning of the programme in December last year, will probably be at the top of the list for to get a booster. But we actually don't know if they need one or not.

"It's a slightly tricky time because by the time we figure out the people who do need a booster we could be in a winter wave of Covid - probably not a very severe wave, but probably a little bit more virus than there is around at the moment."

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It comes as the latest figures continue to show an increase in Covid cases in Scotland, with 9,329 infections confirmed over the past seven days - up by 12 per cent compared to the previous week.

More than four million adults in Scotland have now had a first vaccine dose, taking coverage to 90.2%, with 77.4% of adults now fully vaccinated.

The UK Government is under pressure to reveal what contingency plans are in place to deal with a future Covid variant that evades current vaccines, amid warnings from its scientific advisers that such an outcome could set the battle against the pandemic back a year or more.

Recent papers produced by the government’s Scientific Advisory Group for Emergencies (Sage) have suggested that the evolution somewhere in the world of a variant that evades vaccines is a “realistic possibility”.

Dr Marc Baguelin, from Imperial College’s Covid-19 response team and a member of the government’s SPI-M modelling group, told the Guardian: “It is unlikely that such a new virus evades entirely all immunity from past infection or vaccines.

“Some immunity should remain at least for the most severe outcomes such as death or hospitalisation. We would most likely be able to update the current vaccines to include the emerging strain.

“But doing so would take months and means that we might need to reimpose restrictions if there were a significant public health risk."