A new lab study conducted in the United States suggests that the vaccine produced by Pfizer and BioNTech may be effective against the COVID-19 variant known as P.1, which is a strain that was first identified in travelers from Brazil.

A separate study in Brazil - which is yet to be published - indicates that the CoronaVac vaccine from Chinese company Sinovac may also be effective at neutralizing the P.1 variant, according to an unnamed source who spoke to Reuters on Monday.

There has been widespread concern that current vaccines may be less effective against some mutated strains of the virus.

If substantiated by real-world evidence, the results from the two studies could prove encouraging for international immunization efforts, as the P.1 variant has already spread to more than 20 countries including the United Kingdom. The variant is thought to be more transmissible and possibly capable of reinfecting people who have built up natural immunity to earlier strains.

In the US study, which was published in the New England Journal of Medicine, scientists created an engineered version of the P.1 variant which was then introduced to serum samples taken from people who had previously received the Pfizer vaccine.

The serum samples neutralized the P.1 variant with an efficacy "roughly equivalent" to tests on a strain of the novel coronavirus first isolated in January last year, which were performed for comparison.

The study was led by Liu Yang and Liu Jianying of the University of Texas and supported by researchers from German immunotherapy company BioNTech and US pharmaceutical company Pfizer.

In a separate development, Reuters reported this week that preliminary data from a study in Brazil suggests that the CoronaVac vaccine is effective against the P.1 variant. The study tested blood samples from vaccinated people against the variant, according to the unnamed source who provided no further details. CoronaVac is currently the primary treatment in use in Brazil.

The P.1 variant is responsible for high rates of infection in Brazil and has hit the city of Manaus particularly hard. The northwestern city previously struggled to contain an initial wave of infections last May, when around 80 people died from COVID-19 each day. Health experts had predicted that a second wave was unlikely as studies suggested that around two-thirds of people in Manaus had already been infected.

However, COVID-19 patients began filling hospitals in Manaus once again over the New Year as a second wave surged through the city. The P.1. variant was responsible for the majority of infections, leading experts to theorize that the strain is capable of evading protective immunity arising from infection with previously circulating variants.