The effects of Covid on the body are being studied and so is the effectiveness of the medication given to people for it. A new study has found that the mRNA booster immunisations given extend protection against moderate and severe Covid-19 for four-to-five months. However, after that its effectiveness starts waning away. 

The findings, published in The BMJ, found that in the Omicron period mRNA vaccine protection against severe Covid-19 was initially high (89 per cent) but waned after primary vaccination.

"In our new study, we looked at tens of thousands of patients in multiple states, seen over a year and a half," said researcher Brian Dixon from Indiana University.