But a variant that emerged in southeast England in September is causing particular concern, leading to an emergency lockdown in London over Christmas and causing countries including Canada, France and Germany to halt flights and suspend rail links.
1. Why is this mutation alarming?
Dubbed the “B.1.1.7 lineage,” the strain has undergone almost a dozen genetic changes from the virus that emerged from Wuhan, China in late 2019 — way more than typically observed.
That includes changes in key areas of the virus involved in its ability to infect people. Preliminary analysis in the UK suggests it may be as much as 70% more transmissible than other circulating SARS-CoV-2 strains and may be contributing to a spike in cases in the country.
Maria van Kerkhove, the World Health Organisation’s technical lead on Covid-19, told the BBC on Dec. 20 that the WHO is working to understand the extent to which the virus may spread more easily, along with other human behavioral factors that may be driving transmission.
It’s also looking at whether the mutation causes more severe illness and can evade the antibodies generated by vaccination.
2. What’s known about when it emerged?
The two earliest known specimens were collected in late September in London and the nearby area of Kent, and cases continued to be found through early December.
One reason the new variant proliferated was that its emergence coincided with the festive season traditionally associated with increased family and social mixing. Scientists have hypothesized that the strain may have resulted from the transmission of the virus from a chronically infected patient.
3. How quickly has it spread?
As of Dec. 15, 1,623 virus samples were identified as belonging to the B.1.1.7 lineage. Of these, 519 were collected from patients in Greater London, 555 in Kent, and 545 in other regions of the UK including both Scotland and Wales.
Cases have also been identified in Denmark, the Netherlands, Belgium and Australia. Since only about 10% of SARS-CoV-2 samples from UK patients undergo genetic sequencing, the number of known cases is an underestimate of the true number of infections.
Infection rates in areas where the strain has been circulating have increased faster than expected, Public Health England said on Dec. 20, adding that additional analysis found it has a higher transmission rate than other variants in circulation.
Paul Hunter, a professor of medicine at the University of East Anglia’s Norwich School of Medicine, told the Science Media Centre that the new variant was responsible for 62% of SARS-CoV-2 infections in London in the week ending Dec. 9, up from 28% of infections there in early November.
4. How many other mutations are there?
Viruses constantly change through mutations that arise naturally as they replicate and circulate in their hosts. As a result of this ongoing process, many thousands of mutations and distinct lineages have already arisen in the SARS-CoV-2 genome since the virus emerged in late 2019.
As mutations continue to arise, novel variants are increasingly found, with the vast majority of mutations having no apparent effect on the virus.
However, scientists pay most attention to mutations like those that have occurred in the new UK strain involving the gene that encodes the SARS-CoV-2 spike protein, which is associated with viral entry into cells and influences immunity and vaccine efficacy.
The extent to which SARS-CoV-2 may evolve to escape immunity induced by infection or vaccination isn’t currently known. Studies are under way to understand that better.
The WHO’s van Kerkhove told the BBC that current information suggests that the new variant doesn’t have any impact on the vaccines being rolled out. Over time, as more mutations occur, vaccines may need to be altered.
This happens with seasonal flu, which mutates every year, and the vaccine is adjusted accordingly.
Unlike flu, coronaviruses have a proof-reading mechanism that means they doesn’t mutate as quickly as the flu virus. Covid-19 vaccines that have so far proved effective in trials can be easily tweaked if necessary, the BMJ medical journal reported on Dec. 16.