In a study evaluating the BioNTech-Pfizer COVID-19 vaccine's ability to neutralize the B.1.1.7 ("UK") viral variant, researchers found no loss of immune protection compared to that against the original Wuhan reference strain. Their analysis was based on blood samples from 40 people who had received the BioNTech-Pfizer COVID-19 vaccine during clinical trials. The authors conclude their results show it is "unlikely that the UK variant virus will escape ... protection" as mediated by this vaccine. In September 2020, the SARS-CoV-2 lineage B.1.1.7 was discovered in the United Kingdom. It subsequently increased in prevalence, showed enhanced transmissibility, and spread to other continents. The B.1.1.7 variant has a series of mutations in its spike (S) protein, which it uses to gain entry to host cells. Whether a virus with the large number of mutations found in the spike protein of lineage B.1.1.7 could be neutralized by the blood sera from people who had received the BioNTech-Pfizer COVID-19 vaccine is an important question. To investigate, Alexander Muik, Ugur Sahin and colleagues generated SARS-CoV-2-S pseudoviruses bearing either the Wuhan reference strain or the B.1.1.7 lineage spike protein. They tested these viruses with blood sera of 40 people who had received the BioNTech-Pfizer COVID-19 vaccine following the recommended regimen of two doses administered 21 days apart. The sera had slightly reduced but largely preserved neutralizing titers against the B.1.1.7 lineage pseudovirus, they found. This suggests the UK variant won't "escape" vaccine-mediated protection, as provided by this vaccine. The authors note that the non-replicating pseudovirus system they used may be a potential limitation of the study. They also conclude: "Although sustained neutralization of the current B.1.1.7 variant is reassuring, preparation for potential COVID-19 vaccine strain change is prudent. Adaptation of the vaccine to a new virus strain would be facilitated by the flexibility of mRNA-based vaccine technology."