me patients and antigen selection
[Update: header edited to correct potential selection processes]
The new UK variant appears to be more infectious (but not more pathogenic), according to the UK’s Chief Medical Advisor. That evidence hasn’t been published yet, but its very rapid spread (able to be tracked because of good testing and sequencing in the UK) seems to be a key factor in this conclusion.
A preliminary genomic analysis suggests that lineage B.1.1.7 is unusual. It has 14 amino acid replacements, and three deletions, a large number compared to other variants. Eight of the changes are in the spike protein.
This level of mutation may be due, these authors suggest, to treatments involving convalescent plasma resulting in stronger selection pressure on the virus populations due to high concentrations (or greater diversity) of antibodies and to viral persistence in some patients.
The authors hypothesise
“… that the unusual genetic divergence of lineage B.1.1.7 may have resulted, at least in part, from virus evolution with a chronically-infected individual.”
They stress this remains to be proven. Further laboratory analyses are required.
A new South African variant too
Media reports of another new strain emerging in South Africa (called 501.V2) appeared over the weekend as well. This lineage is reported to have “between 10-20 mutations that were not previously seen in viruses from South Africa prior to September.”
South Africa’s Health Minister commented that “… clinicians have been providing anecdotal evidence of a shift in the clinical epidemiological picture, particularly noting that they are seeing a larger proportion of younger patients with no co-morbidities presenting with critical illness.”
The key words to focus on are “anecdotal evidence.”
Update 22 Dec: A pre-print paper on the new South African variant – called 501Y.V2 – describes eight mutations that define this variant, including three in the spike protein receptor-binding domain. It shares a mutation – N501Y – with the new UK strain (and other mutations seen in other variants). The large number of mutations may involve a combination of persistence of the virus in some patients leading to many more cycles of replication and antigenic selection, where mutations that help avoid antibody neutralisation have an advantage.
Wait for more research
These reports are preliminary. Further research is required to understand the selective processes, the degree or nature of selective advantage (if any), and whether there has been a change in clinical effects in South Africa.
The effectiveness of Covid-19 vaccines already available, and those in development, are usually tested against a variety of viral strains. So it is feasible that the new variants will be susceptible to these vaccines. But that too needs careful scrutiny.
One of the bright spots of 2020 has been that the science system can react very quickly to emerging threats and challenges.