The man tested positive on December 19 but the local authority was not made aware of the results until last Thursday, January 28.
It has led to 10,300 people living in around the WS2 postcode of Walsall being tested for coronavirus, with door-to-door testing starting on Wednesday afternoon.
Councillor Mike Bird, leader of Walsall Council, said: "He was a volunteer in the Oxford trials for the vaccine and tested positive.
"He then self-isolated like he knew he had got to do.
"Since then, what I can say, his partner has tested negative for the virus.
"He works in the IT business for a private employer and his job takes him around the country. He lives in Walsall.
"Sample was taken to a laboratory in Milton Keynes and from there on to a further laboratory in Basildon, where it was further identified for this variant.
"There was a delay in telling us until last Thursday.
"As such, we had to gear up to test 10,000 people in three electoral wards of Birchills Leamore, Blakenhall and Bloxwich East.
"Some of those may be WS2 postcodes but some of them do drift into WS3.
"We believe that obviously he contracted it while he was doing the trial in Oxford.
"He has not been out of the country, so that is why we have got to find out how this variant has appeared.
"Now, we are doing a backtrack as to where he has been before the trials and during the trials, and obviously making sure there is no infection transmitted.
"What we do know is this virus is more prevalent in transmission than the previous ordinary Covid virus that we know.
"They were volunteers, guinea pigs, who were offering themselves and bodies to test the vaccine as it was being produced or invented.
"Hands up to him for being one of those guinea pigs, but sadly he found he was positive."
Speaking about the door-to-door testing, Councillor Bird added: "We will be dropping off self-test kits.
"Hopefully, we can return the results within 72 hours.
"It is testing for the Covid virus, in general, but it will obviously identify Covid-19 and the [new] variant."
It comes as Covid case rates in Walsall have fallen in the last week. Walsall’s seven day rate was at 515 per 100,000 people – a reduction of more than 30 per cent from the week before when the rate was at more than 800.
Two new mobile testing sites were set up in Walsall on Tuesday.
The sites, at Forest Arts Centre and Walsall College, are for people with no symptoms who live or work in the WS2 area.