People who receive the coronavirus vaccine will not be exempted from self-isolation if they are contacted by NHS Test and Trace, it has emerged.
Although the vaccine will give recipients immunity from the virus, scientists do not yet know whether it will stop them being carriers.
Government sources said it was likely to be months before there was any prospect of the vaccine negating the need for self-isolation.
It means that even if someone has been vaccinated, they will still have to remain at home for 14 days if they come into contact with someone who has the virus.
A Government source said: “People who get vaccinated will have to stick to the same rules as everyone else because we don’t know if it stops people being carriers and passing the virus on to others.
“It will take a long time to work out what effect on transmission the vaccine will have.
“We will have to be at a point where a sizeable portion of the population has been vaccinated before we have that evidence.”
The news will be a blow to workers in the NHS, care homes and elsewhere who had hoped that once they had received the vaccine they would be able to work without the risk of having to self-isolate.
It will increase the pressure on the Government to speed up the rollout of mass testing to replace the need for self-isolation.
A pilot scheme which is being trialled in Liverpool allows contacts of people who have tested positive for the virus to have tests every day instead of going into self-isolation.
If they test negative seven days in a row they are given the all-clear.
The Government’s intention is to roll out the scheme nationwide in January if the pilot is deemed to be a success, meaning it will be mass testing, not vaccination, that will hold the key to ending the need for self-isolation.
It will depend, however, on the availability of many millions of lateral flow tests, which give results from a swab in less than 30 minutes. Mr Johnson hopes that more than 500 million of the tests will be available by mid-January.
Any other vaccine that might be approved by regulators, such as the one being developed by Oxford University, will also be subject to the same lengthy process of discovering whether it prevents people being “silent” carriers of the virus.
Jonathan Van-Tam, the deputy chief medical officer, said on Wednesday: “We don't know if this vaccine will prevent transmission, or any of [the vaccines].
“We have to wait for the science to tell us if it will prevent transmission, though we are very hopeful on that point.
“We also have to be patient to see the real live effects on transmission and hospitalisations and deaths, and until we see that as scientists, we can't then scope what the likely impact is going to be on bringing this pandemic to an early end.”