LONDON (Reuters) – Britain is looking at issuing immunity certificates to people who have developed resistance to the coronavirus, but there needs to be more research into the science behind it, health minister Matt Hancock said on Thursday.

People who have had COVID-19, the disease caused by coronavirus, develop antibodies to fight the virus, but it is unclear how long any immunity they develop lasts.

“(An immunity certificate) is an important thing that we will be doing and are looking at but it’s too early in the science of the immunity that comes from having had the disease,” Hancock said at a news conference.

“It’s too early in that science to be able to put clarity around that. I wish that we could but the reason that we can’t is because the science isn’t yet advanced enough.”

Earlier on Thursday, Prime Minister Boris Johnson’s spokesman said that Britain was looking at what other countries were doing and would learn from helpful ideas.

Britain on Thursday pledged to increase testing for the disease to 100,000 daily tests by the end of the month.

Hancock said the country was also working on blood tests to establish whether people had already had the virus and had developed antibodies and therefore some immunity to the disease.

Such tests could potentially be done at home and deliver results in as little as 20 minutes, Hancock said, but first they had to be shown to be accurate.

“We’re currently working with nine companies who’ve offered these tests, and evaluating their effectiveness,” Hancock said.

“These blood tests offer the hope that people who think they’ve had the disease will know they’re immune and can get back to life, as much as possible, as normal. But they’ve got to work.”

(Reporting by Alistair Smout, additional reporting by Andy Bruce and Elizabeth Howcroft, editing by William James and Estelle Shirbon)