A two-shot course of Pfizer Inc.’s vaccine has just 22.5% efficacy against symptomatic infection with the omicron variant, but can thwart severe disease, according to laboratory experiments in South Africa.

Researchers at the Africa Health Research Institute in Durban issued additional data on a small study released earlier this week.

The research considered blood plasma samples from 12 participants. Scientists found omicron resulted in about a 41-fold reduction in levels of neutralizing antibodies produced by people who had received two doses of the Pfizer-BioNTech SE shot, compared with the strain detected in China almost two years ago…

There continues to be sufficient protection against severe disease, they said.