Brazil's top public-health body is warning about the P.1 coronavirus variant, first found in Brazil.
Some mutations may make the virus more resistant to vaccines, Fiocruz said.
Another study published Wednesday indicated P.1 could reinfect people who previously had COVID-19.
A coronavirus variant causing cases to soar in Brazil, Canada, and elsewhere is mutating in "particularly worrying" ways that could make it more resistant to vaccines, researchers from Brazil's leading public-health body have warned.
A new study published Wednesday suggests the variant, known as P.1, is also able to reinfect people who have already caught a coronavirus infection.
Felipe Naveca, a researcher at the public-health body Fiocruz, said the new mutations affected the part of the virus that attaches to cells, called the spike protein, and could make vaccines that target this protein less effective, per Reuters.
"We believe it's another escape mechanism the virus is creating to evade the response of antibodies," Naveca said. He works in the Amazon city of Manaus, where the P.1 variant is believed to have originated in December.
"This is particularly worrying because the virus is continuing to accelerate in its evolution," he added.
Naveca said the new changes appeared to be similar to the mutations seen in the variant first found in South Africa, called B.1.351. In early lab tests, antibodies produced by Pfizer-BioNTech's and Moderna's COVID-19 vaccines couldn't attach as well to B.1.351 compared with the original coronavirus.
In the separate study published Wednesday, researchers said previous coronavirus infection offered 54% to 79% protection against future P.1 infection, compared with protection against COVID-19 infection with other virus strains. The study was conducted by the University of São Paulo, Imperial College London, and Oxford University.
The public-health agency in Canada, where there has been a rise in P.1 cases in recent weeks, said in the statement Thursday that early evidence suggested the P.1 variant might reduce vaccine effectiveness, "making it even more important to control its spread."
P.1 is about twice as contagious as the original virus and has spread to 36 countries, according to the Global Initiative on Sharing All Influenza Data. Just under 500 cases have been reported in the US across 31 states, according to the Centers for Disease Control and Prevention.
In countries where it is prominent, P.1 is infecting a high number of younger people. Brazil hospital data shows that in March more than half of all patients in intensive care were ages 40 or younger, per Reuters.
Ester Sabino, a scientist at the faculty of medicine of the University of Sao Paulo, told Reuters that further mutations of the P.1 variant were not surprising given the fast pace of transmission.
"If you have a high level of transmission, like you have in Brazil at the moment, your risk of new mutations and variants increases," she said.