Extending the time between doses of the Novavax coronavirus vaccine is of “very little concern”, an expert has said.

The chief investigator behind a new highly effective jab from the American firm said leaving a longer gap between jabs is unlikely to have a negative impact on effectiveness – and may even increase it.

Interim trial results suggest the new Novavax vaccine is 89% effective at preventing Covid-19 in people who received two doses of the vaccine 21 days apart.

This was also the schedule used in the Pfizer/BioNTech trial. The Oxford/AstraZeneca vaccine trial had limited data on two doses delivered at least 12 weeks apart.

Experts in the UK have said a second jab can be delayed for up to 12 weeks in a bid to get more people vaccinated sooner.

Professor Paul Heath, principal investigator of the UK arm of the Novavax vaccine trial, said data on efficacy after one dose will be available soon, and researchers know that cases occurred between dose one and dose two.

But he hopes most of those cases occurred in the placebo recipients rather than in those who received the vaccine.

Prof Heath added: “Having said all of that, and thinking about what’s happening in the UK at the moment, this is a subunit protein adjuvant vaccine, and we are very familiar in the UK with varying schedules, if we need to.

“And certainly with a standard vaccine like this, I would have very little concern about extending the interval between doses.”

Prof Heath explained: “Because we know that works with these types of vaccines, and potentially, it may even be better if there is a longer gap between the two doses. I don’t know that at this moment.

“We do know that for the Oxford/AstraZeneca vaccine that the longer the interval, the better the response.

“And so there will be a degree of that also with this vaccine, I suspect.

“We will know more information about one dose efficacy quite soon.”

He added: “What I would come back to is the basic principle here, that with this type of vaccine, the interval between doses is not so important, or rather extending the interval between doses is not so important, and in some cases might lead to a better response.”

Prof Heath gave examples of routine vaccines given to babies.

He said: “For some vaccines we used to give three doses at two, three and four months of age, but we’ve found that by increasing the gap from one month to two months, that’s as good as having the one month interval between them, and in some cases better.”

He added: “We also know for the cervical cancer vaccine that the longer gap is better in terms of immune responses.

“So I think we have knowledge from a range of what are routine vaccines, which is why in practice we are comfortable in doing that.”

Prof Heath said that while the Pfizer vaccine – which many have suggested might not be as effective with an extended interval – is an RNA jab, it is still producing neutralising antibodies against a protein.

“I think therefore we can extrapolate from the experience with other vaccines that produce antibody against protein and expect that the wider the interval the the similar the response, or indeed potentially the better the response,” Prof Heath said.