Coronavirus cases in India: At a time when the number of Covid-19 infection is on the rise in India, a study published in The Lancet suggest that someone infected with the coronavirus has 88 per cent lower chances of hospitalisation or death due to the disease as compared to those not infected previously. The study claims the risk of hospitalisation or death remains low for at least 10 months.
The study said that 65 studies from 19 countries, including India, were part of the systematic review and meta-analysis. The study evaluated the effectiveness of past infection by outcome, variant and time since infection.
It said that studies examining natural immunity in combination with hybrid immunity – or one with vaccination – were excluded from the analyses.
Chances of reinfection from the pre-Omicron variant were lower by 85 per cent
The analysis showed that the chances of reinfection from the pre-Omicron variant were lower by 85 per cent at one month. However, this fell to 79 at 10 months. Similarly, the chance of getting reinfected from the Omicron BA.1 variant was lower by 74 per among those who were infected with the pre-Omicron variant. But in this case, the decline was sharp and reached 36 per cent at around 10 months.
Five studies showed that protection from reinfection remained universally high for 10 months. While it was 90 per cent for ancestral, Alpha and Delta, it was 88 per cent for Omicron BA.1
In the cases where the prior infection was pre-Omicron, the protection against Omicron sub-lineages was reduced significantly. But in cases where the past infection was Omicron, the protection remained at a higher level.
“The weaker cross-variant immunity with the Omicron variant and its sub-lineages reflects the mutations they have that make them escape built-up immunity more easily than other variants,” said co-author Hasan Nassereldine from the Institute for Health Metrics and Evaluation (IHME) at the University of Washington’s School of Medicine, US.
While there have been several studies which focused on how effectively the incidents of past Covid-19 infection reduced the risk of reinfection, none has comprehensively assessed how long this protection lasted and durable they were against different variants.