LONDON (AP) — The British government says all health care staff who work with the public will have to be vaccinated against the coronavirus starting in April, despite concerns the move could drive thousands of people to quit their jobs.

Health Secretary Sajid Javid said Tuesday that 90% of staff in the state-funded National Health Service have already received two doses of a vaccine. But that leaves more than 100,000 health workers unvaccinated.

Javid told lawmakers in the House of Commons that, while vaccination is not compulsory for most people, health workers “carry a unique responsibility” because they are in contact with those most vulnerable to illness.

He said the mandate won’t take effect until April 1, which will give all staff time to receive two doses. There will be exceptions for those who are medically exempt and staff who don’t meet members of the public.

The change applies in England. Scotland, Wales and Northern Ireland set their own health rules.

Trade unions had opposed making vaccinations compulsory, saying it could drive some staff to quit the already stretched health system.

Labour Party health spokesman Jonathan Ashworth said there was a risk “that a policy, however laudable in principle, could exacerbate some of these chronic understaffing problems.”

The government already requires nursing home staff to be vaccinated against COVID-19, with Thursday the deadline. Javid said that since the rule was announced, the number of unvaccinated care workers had fallen from 88,000 to 32,000.

Britain was one of the first countries in the world to start coronavirus vaccinations, but, as in many countries, the campaign has slowed to a crawl after a strong start. About 80% of people over 12 in the U.K. have had two doses of vaccine.

Britain also is offering third booster doses to people at heightened risk from the virus, including everyone over 50.

The U.K. has recorded almost 142,000 coronavirus deaths, the highest total in Europe after Russia.