Current Covid-19 vaccines are less effective against the Delta coronavirus variant, which was first detected in India, but they still prevent severe disease and death, Maria Van Kerkhove, the World Health Organization's technical lead for Covid-19, said on Monday.

"There is a recent study that came out in The Lancet ... that looked at the reduced titer neutralization from the alpha, beta, gamma, and delta variants showing a reduction in neutralization on the delta variant.