The Omicron variant of coronavirus has "substantial" ability to cause reinfection in people who have previously had Covid-19, a study from South Africa suggests.
The research, which has not been peer-reviewed, found people who had tested positive for Covid could pick up the virus again.
It did not say how the variant will behave when spreading in a highly vaccinated population such as Ireland, or whether the virus can evade the protection offered by vaccines against severe disease.
Breakthrough infections are occurring with other variants in those who have had Covid previously and those who are vaccinated.