Elderly people who have received only one vaccine dose appear in some cases to still be vulnerable to the disease. These findings have fuelled growing concerns about the government’s strategy of delaying administering the second dose to care home residents – sometimes by as much as 12 weeks – as opposed to administering the second dose after three weeks as recommended.

According to Professor Martin Vernon, a consultant geriatrician in Greater Manchester and former National Clinical Director for Older People for NHS England, there have been cases of older care home residents coming down with the virus after being vaccinated with the Pfizer vaccine. “I have sight of a reasonably large system of care homes. In just under 20 per cent of them I have experienced outbreaks in the 31 days since vaccination. None of them have received second doses.”

He added: “The difficulty with all of this is that it’s a complex ecosystem in care homes. So some of the cases may have been incubating at the time of vaccination, but some of them for sure have occurred after the 21 day interval post-vaccination.” Under the circumstances, Prof Vernon firmly recommended that the government administer a second dose of the vaccine to the elderly after the recommended 21 days.

How serious these post-vaccination infections are remains unclear. Discussing the cases he has seen, Professor Vernon said “In terms of severity it’s fair to say that in about 30 per cent of cases the individuals are unwell, but attribution to whether that’s Covid-related or other things given how vulnerable these people are is very difficult. The other 70 per cent have either no illness or minor symptoms.”

Professor Vernon was unable to provide any information on whether any of these patients had been sent to hospital or died as a result of their infections. However, speaking to the Financial Times Geoff Butcher, who runs a group of six care homes in the Midlands, claimed five residents of one of his homes had died “directly from Covid” in an outbreak that started three weeks after residents received the Pfizer vaccine.

Concerns about delays to doses and similar stories of post-vaccination outbreaks are shared by other doctors and care home professionals. As early as 21 January, Care England, the UK care sector’s leading representative, wrote to Matt Hancock saying that it would be “pragmatic to re-evaluate the evidence” following reports that elderly care home residents were catching the virus post-vaccination.

Equally, when Professor Vernon expressed his concerns on Twitter, a number of doctors reported they were worried by similar cases they had seen themselves. Eileen Burns, former President of the British Geriatrics Society, retweeted Vernon’s question as to whether others had seen coronavirus infections after vaccination, and added “Yes, so far (thankfully) small numbers. Also staff with proven Covid a month after first jab. Don’t be lulled into a false sense of security. Second doses need to be given asap – as near to the evidential schedule as possible.”

One explanation for these worrying developments might be that the Pfizer vaccine, the first vaccine to be approved and widely distributed to care homes which were top of the priority list, may be somewhat less effective among the elderly, necessitating a second dose. Evidence for this hypothesis comes from recent studies by Gupta Labs. After administering the Pfizer vaccine serum to 23 people, with a median age of 82, seven of the 15 participants over the age of 80 did not “achieve neutralisation of the virus,” i.e. the elimination or reduction of the virus’s ability to replicate. It was only three weeks after receiving the second dose that all 15 achieved neutralisation. While neutralisation tests are not always perfect in determining immunity and the sample size is small the findings provide a possible explanation.

Hearteningly, however, these problems might not affect the AstraZenaca vaccine. A new study by the University of Oxford found that a single dose of the vaccine offered 76 per cent protection up to a period of 12 weeks.

The possibility that post-vaccine infections were being driven by new strains, such as the Brazilian and South African mutations which may be less affected by current vaccines, was deemed unlikely by Professor Vernon. He said that the cases he had seen seemed to be mainly the Kent variant of the virus which spreads more easily but has not sparked the same level of concern about vaccine resistance.

Nonetheless, others continue to support the current policy of delaying the second dose.

In an official statement the British Geriatrics Society expressed support for the policy and said, regarding new outbreaks in care homes: “It is too early to say whether this may warrant a re-evaluation of the vaccination policy, but continued close monitoring is essential and the BGS will continually review its position in light of available evidence.” The BGS also stated: “No vaccine can deliver 100 per cent protection from COVID-19, and there will be cases where those who have been fully vaccinated with both doses do subsequently contract the virus, though their symptoms are likely to be less severe.”

The government also remains insistent that a single dose – with a delayed follow up – is the correct policy.

Responding to enquiries about the issue a Department of Health and Social Care spokesperson said, “Our number one priority is getting vaccines rapidly rolled out to as many older and clinically vulnerable people, as well as our frontline health and social care heroes. The decision by the MHRA to change vaccine dosage intervals followed a thorough review of the data and was in line with the recommendations of the UK’s four Chief Medical Officers.

“Both vaccines provide a high degree of immunity after the first dose, and the Government has closely followed the guidance of the Joint Committee on Vaccination and Immunisation (JCVI) which was clear that we should give as many people as possible some level of immunity initially.”