The high infectivity of this SARS-CoV-2 variant is a challenge, even if it doesn’t trip vaccines
Two nations, the UK and South Africa, have reported two separate mutated SARS-CoV-2 variants as being responsible for a spurt in cases in their respective jurisdictions. Scientists and policymakers are keenly watching the UK variant—the B.1.1.7. lineage—given the mutation seems to have drastically increased the infectivity of this variant; computer models suggest it is 40-70% more transmissible than other variants circulating in the UK and could supplant the other variants. The number of variations noted for B.1.1.7. are also unprecedented; 23 letters in the viral genetic code of 29,903 letters are altered/deleted in this variant, of which, 17 are believed to help it invade human cells—14 amino acid changes and three deletions. Indeed, the GISAID, which tracks SARS-CoV-2 mutations, says that this variant is marked by multiple spike protein—the part of the viral particle that helps it bind to the human cell, mediated by the human receptor protein ACE2—mutations, including D614G and deletion 69-70, two mutations that have been previously tied to increased infectivity. Against the sharp rise in the virus’s transmissibility because of the variant, the R0, or the number of persons an infected person is likely to infect, is expected to concomitantly rise by 0.4.
A consensus among scientists on the likely ramifications of the B.1.1.7. mutations are yet to develop, given key indicators like immune response and lethality will manifest later. Indeed, the WHO, in a release on Monday, has stated that “further epidemiological and virological studies” need to be conducted to understand how the UK variant’s mutations impact the virus’s infectivity and pathogenicity. But, as some scientists have pointed out, even if Covid-19 lethality and severe morbidity stay the same despite the mutations, the increased transmissibility would mean a greater absolute number of deaths and hospitalisations than usual, simply because, now, more people will get infected than the under the earlier R0. The deletion at position 69/70 affects the performance of PCR assays that targets the spike glycoprotein gene—but, given most PCR assays use multiple targets, the impact on testing could be negligible. One of the most important ramification—against the backdrop of many countries preparing to roll out vaccines (the UK has already allowed Pfizer’s)—relates to the mutations’ impact on a vaccine’s effectiveness. While most scientists believe that the mutations won’t have much of an impact, it would still be advisable to conduct relevant studies, especially for top vaccine candidates.
The WHO notes that most mutations in viruses “do not have a direct benefit to the virus or may even be detrimental to its propagation”. While the infectivity-virulence trade-off hypothesis—the deadlier a virus becomes for its host, the less it can spread—has backers in the scientific community, a meta-study of 29 empirical studies published last year in Evolution says more studies are needed to establish this. While SARS-CoV-2 has mutated sluggishly compared to, say, HIV, there were nevertheless some 24,753 single mutations identified from GISAID data by mid-November. Against such a backdrop, countries need to stay prepared to control the spread of the B.1.17. lineage, even if it proves to be a squib at the end.