The Trinity College professor said he has only very mild symptoms and that a self-administered test showed he had the virus within seconds of taking it.
“It just shows the power of antigen testing in a way as it came up [positive] very quick and I then stayed home and that’s what the testing is all about.
"I was amazed, as an immunologist, within two seconds it had moved up the window. The band appeared immediately, whether I was a strong positive or not, it came up very quickly,” Prof O’Neill said on
Today with Claire Byrne.
“I’ve a slight cough and slight sniffles but mercifully enough the vaccine is protecting me, put it that way.
"I was a close contact and I was sent out the three antigen tests by the HSE.
"I took the second one on Friday and it came up positive - a very clear positive by the way. It comes up within seconds in the window. Got my PCR Saturday and my result yesterday so I’m in isolation for the next 10 days,” Prof O’Neill said.
Prof O’Neill joined the chorus of experts calling for the five-month gap between second dose and booster to be narrowed to three months so that more people can receive the booster as soon as possible.
He also said he believes people should receive the booster even if they have had Covid in recent times. Current advice is to wait six months for a booster if you contracted Covid after your initial two doses of the vaccine.
“Boosting is mission one against Omicron. The worry is coming into Christmas we’ll have an increase in socialisation, around 20pc.
“Over 40s have a slight vulnerability and I’d press for getting them done in the next few days.
“Definitely [get rid of the five-month gap]. We have good scientific evidence - there was a great paper in the Lancet Journal - that three months is good for boosting.
“Three months should be the rule now, stop the five months and go for three months for definite to get it done quickly,” Prof O’Neill said.
The UK has taken this move as Boris Johnson predicted a “tidal wave of Omicron” will sweep across the country.
Prof O’Neill said the same move should be done here, along with the opening of the booster campaign to those in their 40s, due to the “remarkable” doubling time of Omicron, meaning how quickly the virus is spreading among the community.
Prof O’Neill said Omicron will take over here as it is “probably three times as transmissible” as the previous Delta variant.
He predicted in the next two to four weeks there will be a big surge in Omicron cases in Ireland and that we should, “hope for the best but plan for the worst”.
The immunology expert said with Omicron, “it’s a numbers game”, because even if most infections are mild, if enough people become infected, “it will put pressure on the health service”.
Immunocompromised children, especially those with siblings, should be vaccinated “as soon as we can” also, Prof O’Neill added.