Toronto, Mar 5 (IANS): Adults infected with the coronavirus in that first wave (March-September 2020) were 40 per cent less likely to become infected during the first six months of Omicron wave (December 2021 to May 2022), a new study has claimed.

Age was also a factor and older adults were less likely to be infected during the omicron wave (dominated by BA.1 and BA.2 sublineages) compared to younger adults, according to the study led by Dr Allison McGeer, Sinai Health System, University of Toronto, Canada, and colleagues.

In addition, vaccination, as expected, also offered substantial protection on top of natural immunity.

"Infection with the original first-wave SARS-CoV-2 virus during March to September 2020 was associated with a 40 per cent reduction in the risk of infection during the Omicron BA.1/BA.2 period from December 2021-May 2022," said the researchers.

Covid-19 vaccination conferred additional protection, and our study "showed younger individuals to be more at risk of infection by Omicron than older age groups."

Compared with adults aged 18-49 years, those aged 50-64 years were 36 per cent less likely to be infected, and those aged 65 years and older 66 per cent less likely.

Multivariable modelling was used to estimate the risk ratio of infection comparing those with and without early SARS-CoV-2 infections, adjusted for age, sex, immunosuppression, household income, calendar time (weeks), number of vaccine doses received, and time from most recent dose.

The results are set to be presented at European Congress of Clinical Microbiology & Infectious Diseases (ECCMID) in Copenhagen, Denmark (April 15-18).