Researchers from Brazil, the U.K., and the U.S., found that plasma from eight people vaccinated five months ago with CoronaVac “failed to efficiently neutralize” the new Amazonian strain, called P.1. The study didn’t show if CoronaVac can still stop people getting sick from the variant, one of the main goals of vaccination campaigns.

While the study’s sample size was small and requires further testing, the fact that all eight samples produced the same result is a “notable phenomenon,” suggesting CoronaVac is less capable of thwarting infections of P.1 than of versions of the virus previously found in Brazil, said William de Souza, of the University of São Paulo in Ribeirão Prêto, one the study’s authors.

Sinovac, the Chinese firm that produces CoronaVac, didn’t respond to requests for comment. In an interview with state-backed broadcaster CGTN that Sinovac released this week, Chief Executive Officer Yin Weidong said that, if necessary, it would take less time to develop a vaccine for the variants than from scratch.