The coronavirus vaccine developed by Pfizer-BioNTech is likely to be just as effective against a highly transmissible mutant strain of the virus that was first discovered in the U.K., according to a study by the two companies.

The variant, known as B.1.1.7., was estimated to have first emerged in the U.K. in September 2020. It has an unusually high number of mutations and is associated with more efficient and rapid transmission.

The characteristics of the variant had led to concerns about the effectiveness of Covid vaccines against it.

However, research published Wednesday on preprint server bioRxiv showed “no biologically significant difference in neutralization activity” between the laboratory tests on the original strain of the coronavirus and the variant known as B.1.1.7.

Authors of the study, which has not yet been peer-reviewed, warned the rapid spread of Covid variants worldwide required “continuous monitoring of the significance of changes for maintained protection by currently authorized vaccines.”