Booster coronavirus jabs will be needed for some people but more evidence is required before any decision is made on a wider rollout of third doses, an expert advising the Government has said.

The Joint Committee on Vaccination and Immunisation (JCVI) is meeting on Thursday to discuss a potential booster campaign and people who might “really need” another jab.

Committee member Professor Adam Finn said a decision is imminent that those who are “very unlikely to be well protected by those first two doses” will need a third one.

His comments on a wider rollout were echoed by another Government adviser, Professor Peter Openshaw, who said further evidence is needed on any benefits booster jabs might bring.

Prof Openshaw, a member of the New and Emerging Respiratory Virus Threats Advisory Group (Nervtag) which advises the Government, also said high case numbers and deaths are “very worrying” and warned that “we just don’t really know what’s going to happen” as winter approaches.

A further 111 people had died within 28 days of testing positive for Covid-19 as of Wednesday, the Government said, while there were a further 33,904 lab-confirmed cases in the UK.

Asked about the figures, Prof Openshaw told Times Radio: “I think it’s very worrying. This is a very large number. If you think, 34,000 people, that’s a lot of people testing positive, and to be seeing over 100 deaths a day at this stage, you know before schools have gone back, while the weather is still relatively good, we’re not back into winter yet.

We’re going into the winter with really very high levels of infection out there in the community and we just don’t really know what’s going to happen

“I think we’re all really anxious about what’s going to happen once we return to normality.”

He added: “We’re going into the winter with really very high levels of infection out there in the community and we just don’t really know what’s going to happen.”

Prof Openshaw said he believes the Government would be “loath” to bring back restrictions for winter, and said the issue is one of “increasing political polarisation”, after scenes in Parliament showed a clear divide in opposition MPs wearing masks and most Conservatives not doing so.

The number of people testing positive for Covid-19 in England has risen, after a two-week period which had seen figures fall.

The latest Test and Trace statistics showed 190,508 people tested positive for Covid-19 at least once in the week to August 11, up 6% on the previous week.

It comes as preliminary research suggests two doses of the Pfizer/BioNTech vaccine appears to have greater effectiveness initially against new Covid-19 infections associated with the Delta variant when compared with the Oxford/AstraZeneca jab, but its efficacy also declines faster.

Prof Finn, who is a professor of paediatrics at the University of Bristol, said the main takeaway from the study, by scientists from the University of Oxford, is that protection from vaccines is “excellent” but that their success in stopping transmission is not as good as they had wished.

He told BBC Breakfast: “At this point I think the main message is that the direct protective effects of these vaccines is excellent, i.e. if you get the vaccination you’re in a much better place in terms of getting sick.

“But the ability of the programme to actually stop the virus from circulating around in the population is less good than we’d hoped.”

Prof Finn urged people to ensure they take up their offer of a first and second dose of a Covid-19 vaccine, but said it is not clear whether a booster jab for all people over a certain age would “make very much difference”.

He said the JCVI will be meeting on Thursday morning, telling the programme: “I think at this point we need to focus on individuals who are more likely, if you like, to get sick again if they’ve not got a booster.”

Prof Finn told BBC Radio 4’s Today programme there is “enough evidence” and the committee will be “imminently deciding that there will be some people who will need a third dose, particularly people who we know are very unlikely to be well protected by those first two doses”.

He added: “But I think we do need more evidence before we can make a firm decision on a much broader booster programme.”

Health Secretary Sajid Javid has previously said preparations for the booster campaign were ongoing and that it could begin in early September, but ministers were awaiting guidance from the clinical experts.

Prof Finn said it is “hard to predict” whether the general rollout of first and second doses will be extended to 12 to 15-year-olds, saying that because children rarely become seriously ill with the virus it could be “a very marginal decision that they will benefit by being immunised”.

As for vaccinating children to protect the more vulnerable, such as grandparents, he said it is “a tricky one” to decide as it is a “much more comfortable” and “clear cut” approach to immunise people where they themselves benefit.

Meanwhile, the latest data on the NHS Covid-19 app in England and Wales showed another fall in alerts and venue check-ins.

A total of 261,453 alerts were sent in the week to August 11, down 18% on the previous week, while there were 1.3 million venue check-ins, down from 1.8 million the previous week.

Check-ins have fallen sharply after running at more than 10 million a week throughout June and the first half of July.