BEIJING, China -- A study by Chinese researchers has found that the Covid-19 booster vaccination can markedly reduce the immune escape of the Omicron variant, underscoring the necessity for the eligible population to get a third booster jab to combat the pandemic.

The researchers from Fudan University and Pigentech Lab revealed that sera from individuals vaccinated with two doses of an inactivated whole-virion vaccine show weak to no neutralization efficacy.

However, the boosters, either homologous or heterologous ones, can markedly improve neutralization titers against all Omicron sub-lineages, according to the study published recently in the journal Cell Host and Microbe.

The Omicron variant has evolved into four sub-lineages -- BA.1, BA.1.1, BA.2 and BA.3 -- and BA.2 is the dominant one worldwide. The neutralization titers for Omicron sub-lineages were significantly reduced, by more than 100-fold, in comparison to those for the virus wild type, according to the study.

The researchers collected and tested 20 samples from healthy adults who had received a third booster shot of the same inactivated vaccine and found that the sera had a five to six folds potency reduction against Omicron sub-lineages compared to that against the wild type, according to the study.

They also tested sera from 18 individuals that received two doses of inactivated vaccines plus one protein subunit vaccine four to eight months later. This cohort also showed higher neutralizing titers than the two-dose recipients.

Noting that the Omicron sub-lineages threaten the neutralization efficacy of current vaccines, the researchers said increasing the rate of full immunization and vaccine booster dose can be an effective means to prevent Covid-19 transmission.