Britain's health secretary, Sajid Javid, has been warned that his plans to make COVID-19 vaccines mandatory for all National Health Service, or NHS, workers could spark a mass exodus of staff.

The proposal to mandate the vaccine for all health service staff was first reported by the Daily Telegraph in May, when government ministers said the policy would "save lives" by reducing the spread of the virus in hospitals.

The newspaper reported on Sunday that an official consultation on COVID-19 vaccines becoming a condition of employment by the health service will be launched as soon as this week.

NHS data shows 190,000 healthcare workers had not received a dose of the vaccine by April, and the Telegraph said that it was as many as one in four in certain hospitals. It noted that a Facebook group, called "NHS workers for choice, no restrictions for declining a vaccine" has gathered nearly 2,600 members.

The care home sector is suffering its worst-ever staffing shortage, partly as a result of mandatory vaccines, ITV News reported last week. The government has said all care home workers, including agency workers, volunteers, and healthcare visitors — must have had their first jab by Sept 16 and be fully vaccinated by Nov 11.

The Telegraph said some experts believe the policy could result in up to 7 percent of care home staff either quitting or being sacked. The government's own data predicts that up to 40,000 of more than half a million care workers will not be fully vaccinated by Nov 11.

The Independent newspaper noted that public and health sector union Unison this week called on the government to abandon the "no jab, no job" policy, telling ministers that they are "sleepwalking into disaster". Unison warned the care sector already has staff vacancy levels of more than 110,000.

The Guardian reported that care home staff are leaving for better-paid jobs, including at Amazon's warehouses.

A Department of Health spokesman said: "NHS staff have a duty of care to those most vulnerable to COVID-19 and we are encouraging all frontline staff to come forward for the jab.

"Ensuring the NHS is well-staffed is a top priority for this government and we will continue to work with employers to ensure they have the right number of staff to meet increasing demand."

British media reported on Sunday that vaccines will soon be offered to children aged between 12 and 15, despite the independent Joint Commission for Vaccination and Immunisation advising the government against the move, claiming the virus posed such a low risk to people in the age group.

Sky News reported that the United Kingdom's four chief medical officers, including England's Chris Whitty, have been asked to make a final recommendation.

The government's vaccine minister, Nadhim Zahawi, has confirmed vaccine passports will be required to gain entry to large venues. He told Sky News the documents are the best way to avoid winter closures because of groups of people mixing in close proximity.

Prime Minister Boris Johnson announced in July that the requirement would likely be imposed on large venues after making it mandatory for all nightclubs in England by the end of this month.

However, many Conservative Party politicians are strongly against the documents being used, and the government is likely to face claims that a policy of effectively mandating vaccinations would be "discriminatory".

Meanwhile, Britain's former Labour Party prime minister, Gordon Brown, has called for G7 nations to urgently create a plan to get COVID-19 vaccine supplies to the developing world. He urged Johnson to convene a G7 summit within the next two weeks.