Luke O'Neill says the now-dominant COVID-19 variant in Ireland could have slightly different symptoms to its predecessors.
The Trinity College immunologist was speaking as BA.5, described as an Omicron 'sibling', is the latest version of the virus and is becoming dominant all over the world.
The subvariant is more infectious than previous ones, and is better able to evade immunity from vaccines and previous infections.
Prof O'Neill told The Pat Kenny Show: "Most cases in Ireland at the moment would be BA.5, for instance, same in the US.
"It's another curveball that has been thrown at us by this virus, and BA.5 is the dominant variant that's out there at the moment".
He says there are some differences to this one.
"One extra symptom for BA.5 I saw this morning is night sweats.
"The disease is slightly different because the virus has changed.
"There is some immunity to it, with the T cells and so on.
"And that mix of your immune system and the virus being slightly different might give rise to a slightly different disease - with strangely enough - night sweats being a feature.
"But very importantly if you're vaccinated and you're boosted, it doesn't progress into severe disease".
On vaccines, Prof O'Neill believes there will new versions for the winter.
"Both Pfizer and Moderna have said they'll have an Omicron vaccine by September, and they'll have a BA.4/5 by October.
"So when we get to that point, it would make sense to start using those newer ones.
"But... the current one is still giving good protection anyway.
"Like the flu, you'll change the vaccine based on the variant that's around at the time".
He adds: "Remember the ones who are getting sickest are unvaccinated, or haven't had the booster.
"Hence the message: get the booster because it will give you this added protection".