Sinovac Vaccine May Not Trigger Sufficient Antibody Response to Brazil Variant: Study

By Reuters Staff

March 08, 2021

BEIJING (Reuters) - Sinovac Biotech's COVID-19 vaccine may not trigger sufficient antibody responses against a new variant identified in Brazil, a small-sample lab study showed.

The emergence of variants of the new coronavirus has raised concern that vaccines and treatments that were developed based on previous strains may not work as robustly.

The study team tested plasma samples taken both from recovered COVID-19 patients and eight people vaccinated with Sinovac's CoronaVac and tested its ability to neutralize the P.1 virus variant that emerged late last year in Brazil's Amazonas state (also known as 20J/501Y.V3). They compared this to the serum neutralization against Brazil's previously circulating lineage, according to the paper published on Monday ahead of peer-review.

Plasma from COVID-19 convalescent blood donors "had 6-fold less neutralizing capacity against the P.1 than against the B-lineage. Moreover, five months after booster immunization with CoronaVac, plasma from vaccinated individuals failed to efficiently neutralize P.1 lineage isolates," the study found.

"These results suggest that P.1 virus might escape from neutralizing antibodies induced by... CoronaVac," researchers at the University of São Paulo in Brazil, Washington University School of Medicine in the United States, and other institutions said in the paper published on the Lancet preprint server.

CoronaVac is being used in mass vaccination drives in countries including China, Brazil, Indonesia and Turkey.

Preliminary results from Phase 3 trials conducted in Brazil that were reported in January estimated a 50.4% overall vaccine efficacy.

Although the study suggests re-infection may occur in vaccinated individuals, the protection given by CoronaVac against severe COVID-19 may indicate other mechanisms in the human immune system, aside from antibodies, may also contribute to reducing disease severity, the current study's authors said.

A Sinovac spokesman was not immediately available for comment. Chief executive Yin Weidong said in a programme aired by state-backed broadcaster CGTN on Thursday the company is "fully capable" of using current research and manufacturing capacity to develop a new vaccine against variants if necessary.

He also said the process would take much less time than it took to develop CoronaVac.

SOURCE: Preprints with The Lancet, online March 1, 2021.