Coronaviruses, including the one that caused COVID-19, continually mutate as they spread from person to person. These mutations can make the virus better at infecting cells or cause more serious illness. They can also change how the virus escapes the body’s immune system or gets detected by testing methods.
During the peak of the COVID-19 pandemic in late 2020/early 2021, several new variants appeared. The most concerning was Delta (B.1.617.2), which was significantly more transmissible and accounted for the majority of outbreak-related cases and deaths [26]. Delta has a number of mutations in its spike protein, such as T478K, P681R and L452R, that are known to alter the ability of the virus to spread and to evade antibody neutralization.
Other significant variants included Alpha (B.1.1.7), which appeared in Britain in November 2020 and quickly became the dominant variant around the world; it later faded away as the more aggressive Delta took over. Also of concern was the emergence of the Omicron sublineage, particularly XFG and BA.2.75 – both of which have been associated with more virulent and severe disease and higher rates of transmission.
Vaccination is the main way to protect against these viruses and their dangerous mutations. However, some of these mutations can reduce the effectiveness of vaccines. For this reason, WHO characterizes some of these emerging variants as Variants of Concern or Interest and tracks their spread through genomic surveillance (see the table below).