The Covid-19 vaccine appears to have “broken the chain” between catching coronavirus and becoming seriously ill, the chief executive of NHS Providers has said.

Chris Hopson said the number of people in hospital with the Covid-19 variant first detected in India, also known as the Delta variant, was not increasing “very significantly”.

He told BBC Breakfast that many of those in hospital in Bolton – which has the highest number of cases of the Indian variant in England – were younger than in previous waves of the pandemic.

It is understood there are GPs in Bolton who have begun offering vaccines at a 28-day gap, in the face of pressure not to waste any doses.

Some patients are believed to have been contacted by text message to say they are eligible for a second jab after four weeks, rather than the eight to 12 week gap advised by the Joint Committee on Vaccination and Immunisation (JCVI).

Comments on the NHS Bolton Clinical Commissioning Group (CCG) Facebook page indicate 16 and 17-year-olds are being offered a vaccine.

Under JCVI guidance, individuals aged 16 years and above with underlying health conditions which put them at higher risk of serious disease and mortality from Covid-19 were included in the top nine priority groups for a vaccine in phase one of the UK’s rollout.

Speaking about hospitals, Mr Hopson said on Saturday: “The people who came in this time round were actually a lot younger and were a lot less at risk of very serious complication, less at risk of death, and what that means is that they were less demand on critical care.

“What we think we can start to say now, based on that experience, is that it does look as though the vaccines have broken the chain between catching Covid-19 and potentially being very, very seriously ill and potentially dying.

“There were very, very few people who have had those double jabs and had been able to have that build-up of protection after those jabs.”

Mr Hopson said in the most recent phase of the pandemic the number of people in hospital in Bolton with Covid-19 peaked at 50, compared to 170 in November and 150 in January and February.

“Infection rates have been increasing in a number of different places,” Mr Hopson said.

“We know that the hospitalisations are increasing, the rates of people coming into hospital in those areas are rising. But they are not rising very significantly.

Of the 12,431 Indian variant cases so far confirmed in the UK, 10,797 are in England, 1,511 in Scotland, 97 in Wales and 26 in Northern Ireland.

In England, the cases are spread across the country, and the most affected areas include Bolton in Greater Manchester (2,149 cases), Blackburn with Darwen in Lancashire (724), Bedford (608), Leicester (349), Manchester (278) and Birmingham (223).

Dr Adam Kucharski, an epidemiologist at the London School of Hygiene and Tropical Medicine, said the transmissibility of the Indian variant could see a “big number” of people admitted to hospital with coronavirus.

A member of the Scientific Pandemic Influenza Group on Modelling (Spi-M) Government advisory panel, Dr Adam told BBC Radio 4’s Today programme there were a “number of concerning signs” following early evidence that first-dose vaccines are not as effective against the Delta variant.

He added: “I think it is particularly this increase in transmission that is potentially going to cause us considerable problems.”

Dr Kurcharski said the current picture meant that it was “hard to be confident” that a “big number” of people will not end up in hospital due to the spread of the Indian variant and the number of adults still unvaccinated in the UK.