3rd dose of Oxford-AstraZeneca jab after six months boosts defences to fight variants

 Delaying a second dose of the Oxford-AstraZeneca vaccine by almost a year results in better protection against Covid-19, a study suggests – while adding a third jab six months later boosts defences even further.

University of Oxford researchers found that delaying a second jab up to 45 weeks after the first results in increased antibody levels – a key part of the body’s immune response – offering greater flexibility in vaccination schedules. A third dose six months after the second resulted in a further increase in antibody levels, they also found, mitigating scientists’ concerns that the design of the Oxford vaccine would limit repeated use.

In the trial, 30 people aged between 18 and 55 years old received a late second dose of the Oxford-AstraZeneca vaccine – an average 44 weeks after first dose – and their antibody levels were found to be higher than those who had their second jab between eight and 12 weeks after the first.

Some 90 people in the trial received a third dose six months after their second and antibody levels were “significantly higher” following a third dose when compared with the response 28 days after a second dose. T-cell responses – another key part of the immune system – were also boosted after a third dose. Reactogenicity – common “expected” adverse reactions – after a late second dose or a third dose was lower than reactogenicity after a first dose.

The findings are important given that the majority of approved coronavirus vaccines are given in a two-dose primary schedule, and it is possible that further doses may be required to maintain protective immunity or control emerging variants.

The research team concluded: “For the first time, we demonstrate that a third dose of [the Oxford vaccine] can induce a strong boost to immune responses to [Covid-19], and that these responses result in higher neutralising antibody titers and enhanced activity against variants.

“We also demonstrate here that a prolonged interval between first and second dose vaccinations results in a significantly higher antibody response after the second dose. This is consistent with previous data demonstrating a longer interval between first and second dose results in an increase in antibody titers, thus providing further reassurance that a delay in second dose will not compromise the level of protection attained after the second dose.”

Although it is currently unknown if booster vaccinations against Covid-19 will be required, perhaps to counter waning immunity or to boost protection against emerging variants, the researchers have shown that a third dose of the Oxford vaccine is “well tolerated” and “significantly boosts” antibody levels above those measured after the second dose. The research team also said their findings are particularly important for countries where administration of a second dose is delayed because of a shortage of supply.

Professor Sir Andrew Pollard, head of the Oxford Vaccine Group, said: “There is an excellent response to a second dose, even after a 10-month delay from the first… Boosters are much more about if protection gets lost over time – and we don’t know that – but if it does, could you boost? And the answer to that from these data is yes, you could. There’s no indication today that we need boosters, and it is something where we need to keep looking at the data and make decisions as the months go by, about whether that protection that we have is lost.”

He said experts will “expect to see immunity start to wane over time because that does happen” but it will not go back “down to zero”.

The Lancet preprint study, which has yet to be peer-reviewed, comes as some “grab a jab” centres offering second dose of vaccines to anyone who had their first dose more than 21 days previously were slapped down by the NHS. Officials said the centres, including the Science Museum in London, should be following advice from the Joint Committee on Vaccination and Immunisation (JCVI) and only offering second jabs to people at least eight weeks after their first dose.

A spokesman for the NHS in London said: “We have made it clear that the Science Museum and other sites should not be giving second dose vaccinations earlier than the JCVI recommends (eight weeks). Those now attending for a second jab ahead of schedule will be turned away.”

https://inews.co.uk/news/health/covid-19-vaccines-delaying-second-dose-of-oxford-astrazeneca-jab-by-almost-a-year-gives-better-protection-1074750