Booster Coronavac dose increases immunity against COVID-19: study

A team of Chinese scientists has reported that a third dose of an inactivated COVID-19 vaccine could effectively strengthen people's immunity against the coronavirus, including the heavily mutated Omicron variant.

Scientists from the Chinese Academy of Sciences (CAS), Peking Union Medical College, the Academy of Military Medical Sciences and the National Institutes for Food and Drug Control examined serum specimens from individuals who had received two or three doses of the inactivated Coronavac vaccine.

They found that the seroconversion rates of neutralizing antibodies were respectively 3.3 percent and 95 percent for two and three-dose recipients, according to a study published in Nature on Friday.

The researchers also isolated 323 human monoclonal antibodies (mAbs) derived from memory B cells in three-dose recipients, half of which recognized the receptor binding domain, the antigen on the virus' spike protein.

Therapeutic treatments with representative, broadly neutralizing mAbs were highly protective against SARS-CoV-2 Beta and Omicron infections in mice, according to the study.

The researchers estimated that a vaccine booster dose could help protect against severe COVID-19 symptoms, although the mean neutralization antibody titer of Omicron for three-dose recipients was lower than that of the original virus.

Wang Xiangxi, a researcher at the Institute of Biophysics under CAS and a co-corresponding author of the paper, said that the results of the study rationalize the use of three-dose immunization regimens.