New Delhi, Feb 17 (IANS): For people who have been infected with Covid-19 at least once before, natural immunity against severe disease (hospitalisation and death) was strong and long-lasting for all variants (88 per cent or greater at 10 months post infection), a largest review and meta-analysis published in The Lancet has revealed.

Past infection with pre-Omicron variants provided substantially reduced natural immunity protection against reinfection with Omicron BA.1 (36 per cent at 10 months after infection).

The researchers said we should recognise the natural immunity in people who have recently been infected with Covid-19, but warn that their findings should not discourage vaccination because it is the safest way to acquire immunity.

For someone previously infected with Covid-19, their risk of hospitalization or death is 88 per cent lower for at least 10 months compared to those who had not been previously infected, according to a systematic review and meta-analysis.

The analysis also suggests that the level and duration of protection against reinfection, symptomatic disease and severe illness is at least on a par with that provided by two doses of the mRNA vaccines (Moderna, Pfizer-BioNtech) for ancestral, Alpha, Delta and Omicron BA.1 variants.

The study did not include data on infection from Omicron XBB and its sub-lineages.

"Vaccination is the safest way to acquire immunity, whereas acquiring natural immunity must be weighed against the risks of severe illness and death associated with the initial infection," says lead author Dr Stephen Lim from the Institute for Health Metrics and Evaluation (IHME) at the University of Washington's School of Medicine.

The review and meta-analysis included 65 studies from 19 countries.

"Vaccines continue to be important for everyone in order to protect high-risk populations such as those who are over 60 years of age and those with comorbidities," said IHME co-author Dr Caroline Stein.