But plans for a widespread booster campaign have been thrown into doubt after reports that only a select few will be offered third doses initially. Leading epidemiologist Professor Tim Spector said that in a worst-case scenario, protection could drop below 50 percent for the elderly and healthcare workers by winter. He said: “A decision on booster doses needs to be made soon by the Joint Committee on Vaccination and Immunisation.
“If we’re going to minimise deaths, they need to get on with it.”
The analysis used swab test results from more than a million users of the Zoe Covid study app.
It found that for the Pfizer/BioNTech vaccine, protection against infection fell from 88 percent a month after the second dose to 74 percent after five to six months.
For the Oxford/AstraZeneca jab, protection dropped from 77 to 67 percent after four to five months.
Researchers said the majority of people who had their vaccines earlier in the rollout were either older, healthcare workers or vulnerable due to underlying health conditions.
They warned that those groups may now be at increased risk compared to people vaccinated more recently.
Prof Spector, lead scientist on the Zoe Covid study app, said: “While vaccines are working well against the Delta variant for the first few months and reducing severe disease, looking at over one million vaccinated Zoe loggers, effectiveness appears to be waning, which could explain recent breakthrough infections in fully vaccinated people.
“We urgently need to make plans for vaccine boosters and, based on vaccine resources, decide if a strategy to vaccinate children is sensible if our aim is to reduce deaths and hospital admissions.
“Waning protection is to be expected and is not a reason to not get vaccinated.
“Vaccines still provide high levels of protection for the majority of the population, especially against the Delta variant, so we still need as many people as possible to get fully vaccinated.”
There were 35,847 new Covid cases confirmed across the UK yesterday and 149 deaths.
More than 47.7 million people have now received a first vaccine, including 42 million who have had both jabs. In April, the Government announced it had ordered 60 million further doses of the Pfizer vaccine in preparation for boosters.
The UK has also secured millions of doses of other vaccines that have not yet been used.
NHS England has been preparing to start the drive as early as September 6, alongside its annual flu campaign.
Health Secretary Sajid Javid last week said he was confident third doses would start in September for the most vulnerable.
But ministers are still awaiting final advice from the Joint Committee on Vaccination and Immunisation before confirming further details.
Interim JCVI guidance in June said the groups to be prioritised should include the immunosuppressed, care home residents and older age groups.
However, it was claimed yesterday that boosters may initially only be recommended for those with weakened immune systems. A source close to the discussions reportedly said only “a few hundred thousand people” would get boosters in the first phase, and healthy elderly people may have to wait.
An official decision is expected to be announced within days.
Other experts said it was important to note that the Zoe study did not look at vaccine efficacy against severe disease, which is generally higher than efficacy against infection and mild disease. JCVI member Professor Adam Finn said other research suggested the vaccines were still good at preventing severe Covid.
He said: “That’s encouraging actually, that people who’ve had two doses are still very much well protected against serious illness, which is our main objective.
“But we do need to watch out very carefully to see if this waning begins to translate into occurrence of more severe cases because then boosters will be needed.”
Dr Simon Clarke, from the University of Reading, said: “The claim that immunity levels will hit around 50 percent by Christmas is not based on any robust analysis of data, and seems more like a finger in the air prediction.
“Immunity is a complex process and we cannot assume people’s immunity will fade at a uniform rate over time.”
Professor Ravindra Gupta, a Government adviser, said he was concerned about cases rising in the coming months.
He said: “In my personal view, the immunosuppressed and individuals over 80 need to be boosted.”
A Government spokesman said: “We are preparing for a booster programme to ensure those most vulnerable to Covid have protection extended ahead of winter and against new variants.
“Any booster programme will be based on the final advice of the independent Joint Committee on Vaccination and Immunisation.”