Glasgow is among a world-first clinical trial to test whether a third booster vaccine could protect people against Covid-19 and its variants.

Some 2,886 people aged 30 and older are being recruited at 18 NHS sites from Glasgow to London, with the first booster jabs administered in early June.

Scientists want people who received their first dose of either Pfizer/BioNTech or AstraZeneca in December or January to sign up.

They hope people aged 75 and over will also come forward.

Seven existing vaccines are to be tested in the Cov-Boost trial to see which jabs could be used in any forthcoming autumn vaccination programme.

Experts believe that all will boost immunity, and lab studies will check their response to variants circulating in the UK, including those from India, Kent and South Africa.

The £19.3 million clinical trial will test three of the vaccines at a half dose, with experts expecting an adequate immune response at this level.

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The half doses will inform whether side-effects are reduced at a lower dose, and could offer useful information to countries where vaccine supply may be more scarce.

The 18 sites will be split into three groups, with each group testing a different set of vaccines.

All of the information will be fed to the Joint Committee on Vaccination and Immunisation (JCVI) at the end of August or early September.

The JCVI will then guide the Government on whether people should be boosted with a third dose and which vaccines should be used, depending on supply.

Among the information gathered will be any data on side-effects, including among people whose third booster jab is a different type to that used for their first two shots.

Professor Saul Faust, director of the National Institute for Health Research Southampton clinical research facility and lead investigator for the trial, said: “The hope of a booster is that we raise the antibody level enough to be able to cover existing and variant strains of coronavirus.”

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He added: “We’re hoping the immune responses will be high enough to protect people against all the strains circulating in the UK, including we’ll be testing in the lab against the Indian variant, the South African variant, the Kent variant as well as the original strain.”

Experts believe booster shots of existing vaccines could be enough to provide protection against all variants.

Additionally, some scientists have suggested that developing new vaccines against variant strains may actually impair people’s immune responses.

All participants in the trial will have bloods taken to measure their immune responses at days 28, 84, 308 and 365 of the trial – with a small number having blood tests at other times.

The sites include Southampton, London, Leicester, Bournemouth, Portsmouth, Wrexham, Bradford, Oxford, Glasgow, Leeds, Cambridge, Birmingham, Brighton, Stockport, Liverpool and Exeter.

People can sign up for the new trial at covboost.org.uk