The UK government has ruled out narrowing the gap between doses of coronavirus vaccine for care home residents, resisting pressure from the sector to reconsider its contentious decision to delay the second inoculation to help stretch supplies.

Care England wrote to Matt Hancock, health secretary, and Chris Whitty, England’s chief medical officer, on January 21, suggesting it would be “pragmatic to re-evaluate the evidence” for spacing out the shots more widely, amid reports of elderly residents catching the disease weeks after receiving their first shot.

As ministers race to meet a deadline of mid-February for vaccinating everyone aged over 70 plus health and care workers, the government has opted to leave a gap of up to 12 weeks between doses to maximise the number receiving at least one vaccination. One person familiar with discussions said in practice the gap was likely to be about 11 weeks.

Asked if there was a prospect of accelerating the second jab in care homes, Helen Whately, care minister, told the BBC’s Today programme: “I’m not expecting to do that because we want to protect as many people as we possibly can by getting the first jab to them.”

Later on Monday, Mr Hancock told a Number 10 media briefing: “We have visited every eligible care home with older residents in England and offered vaccinations to all of their residents and staff. This has been an incredible example of health and social care working side by side to protect people who are in the most need.”

Martin Green, chief executive of Care England, which represents care home operators, praised the speed and effectiveness of the rollout. But he added that a second dose within a shorter timescale “might help protect those most at risk of severe disease and mortality and also alleviate the burden upon the NHS by preventing hospitalisation”. Care England is also seeking assurances that there will be adequate supplies of the second dose.

Deaths in care homes with Covid-19 on the death certificate have risen by about a third in England and Wales over the past week.

On December 31, the UK’s four chief medical officers said they were “confident that based on publicly available data as well as data available to the [Joint Committee on Vaccination and Immunisation] . . . that the first dose of either Pfizer or [AstraZeneca] vaccine provides substantial protection within two to three weeks of vaccination for clinical disease, and in particular severe Covid disease”.

Geoff Butcher, who runs a group of six care homes in the Midlands, said it had completed inoculation of all its residents over a week ago. However, in one of its homes more than half the residents had recently tested positive for the virus in an outbreak that had started three weeks after receiving the Pfizer vaccine.

Five had since died “directly from Covid . . . these are people who were elderly and frail but we [previously] had no concerns about them and they’ve all got Covid on their death certificate”, he added.

Martin Vernon, a consultant geriatrician in Greater Manchester and formerly a senior official in charge of care for older people at NHS England, said he had recently seen “a substantial outbreak” in a fully vaccinated care home that would have been due for the second dose round about now, within the 21 day interval. “Unfortunately some of those people are now very poorly,” he added.

Prof Vernon likened the choice to go against the three week dosing interval tested by Pfizer during clinical trials, to the decision, about a year ago, to move people out of hospital and into care homes without testing them for the disease, helping to spread the virus.

“We are knowingly being instructed to expose one of the most vulnerable groups a second time around to a level of risk that we cannot easily quantify but can anticipate to be higher than if we had followed the available scientific evidence,” Prof Vernon said.

The health department said: “[The approved vaccines] provide a high degree of protection after the first dose, and the government has closely followed the guidance of the Joint Committee on Vaccination and Immunisation which was clear that we should give as many people as possible some level of immunity initially.”

Additional reporting by John Burn-Murdoch