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Denmark: Statens Serum Institute (SSI) Estimate Of COVID Variant B.1.1.7 Growth
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With the exception of the D614G mutation - which appeared in Europe eleven months ago and is credited with increasing its transmissibility over the asian lineage - for nearly a year the SARS-CoV-2 virus has remained functionally stable.
Many other mutations have been documented, of course, but none appeared to enhance the virus's transmissibility or virulence.
Researchers have remained cautiously optimistic that the virus would remain susceptible to the vaccines under development, at least in the short term.
Over the past three weeks, however, some of that confidence has begun to unravel, with the discovery of two COVID variants; one (B.1.1.7) that appears to be 70% more transmissible than the previous virus, and another (501Y.V2) that may be more transmissible, and might be less susceptible to the vaccine.
Viruses evolve, and no one should be surprised to learn that SARS-CoV-2 is a moving target.
As community immunity to the virus grows - either through natural infection or vaccination - the more evolutionary pressure there is for the virus to reinvent itself in order to survive. It's why influenza returns every year, despite acquired immunity and vaccines.
Suddenly, we find ourselves in a race against two variants (and likely more on the way) that could seriously change the COVID-19 pandemic's dynamics.
- B.1.1.7 - first discovered in the UK - and now detected in more than 40 countries, appears to be the most immediate threat. It has successfully become the dominant strain in most of the UK, and - unless something more competitive emerges - appears on track to become the dominant strain globally in 2021.
- 501Y.V2 - which was first identified in South Africa - has already been detected in 6 other nations (see WHO Epidemiological Report - 5 Jan). Like B.1.1.7 it is believed to have a transmissibility advantage over older strains, and some preliminary research suggests it's E484K mutation may render it less susceptible to the current crop of vaccines.
While it is too soon to say how much of an impact it might have, other variants with the E484K mutation have turned up recently in Argentina and Brazil. The good news is most variants will prove to be evolutionary failures, or will provide no functional advantage to the virus.
But with every new infection, the virus is essentially rolling the genetic dice. And the more opportunities is is given, the better the odds are that it will roll the right combination to reinvent itself again.
Which is why reducing the spread of SARS-Cov-2 - and in particular, the more transmissible variants - is viewed as critical right now. A 70% transmissibility advantage - as estimated with the B.1.1.7 variant - is enough to turn it into the dominant strain anywhere it is introduced in a matter of weeks.
Overnight Denmark's Statens Serum Institut (SSI) published a cautionary report, estimating just how quickly their (currently) low number of B.1.1.7 variant cases could explode in their population.
While modeled for Denmark, this is the scenario that many nations may be facing in the months ahead.
First the (translated) summary from the SSI (with a link to the full report), then I'll return with a brief postscript:
Spread of the English virus variant - cluster B.1.1.7
The Statens Serum Institut warns that the English virus variant cluster B.1.1.7 can spread sharply in Denmark if it does not succeed in reducing the number of infections significantly.
Last edited January 5, 2021
The prevalence of the English virus variant, B.1.1.7, is still at a low level in Denmark. SSI expects that the variant will become more widespread in the near future, and therefore it is recommended that further measures be introduced to keep the spread of covid-19 in Denmark under control.
The prevalence of the English virus variant, B.1.1.7, is still at a low level in Denmark. SSI expects that the variant will become more widespread in the near future, and therefore it is recommended that further measures be introduced to keep the spread of covid-19 in Denmark under control.
“It has been assessed on the basis of samples from the genome genome sequencing that the infection from the English variant is 72 per cent. higher than the average of the other virus variants in Denmark. At the same time, it has been seen in England that the contact number for the new virus variant is 1.5 times higher compared to other variants.
This means that the new variant can already in 40-50 days make up half of all cases of infection in Denmark ” - Doctor Camilla Holten M?ller, general manager of the expert group
The growth rate of the English virus variant cluster B.1.1.7 is estimated in a new note from the expert group for mathematical modeling of covid-19 , led by SSI
Although the overall level of infection and contact numbers currently appear to be declining, SSI expects the infection to rise again anyway. This is because as the English variant spreads, the infection will increase exponentially. It shows calculations made by the expert group .
Scenarios for development in Denmark
If the current contact number of 0.96 does not change, the number of daily infections is expected to exceed 4,000 by the end of February.
If, on the other hand, it is possible to lower the contact number to 0.8 for the old variants, the infection can be kept under control for a longer period, after which it will increase again.
If the increase in infection is to be completely curbed, however, it is necessary to reduce the contact number for the old variants to 0.7 (corresponding to 1.05 for the English variant). It is against this background that SSI recommends further restrictions and measures. We managed to lower the contact number to approximately that level during the closure in March and April 2020.
Expected number of infected with cluster B.1.1.7, depending on the number of contacts, 1 January 2021 to 31 March 2021
(Source: SSI)
It is the health authorities' assessment that it is crucial to turn the epidemic curve around and get the contact number significantly below 1 in the coming weeks, so that the infection rates are as low as possible when cluster B.1.1.7 becomes the dominant virus in mid-February. As large parts of society have been shut down, it is expected that infection can occur to a greater extent in connection with gatherings inside and outside the home, and that tightening the assembly ban from 10 to 5 people in the public space is a necessary measure to prevent serious spread of infection.
In all but their best case scenario, they consider it likely that it is a matter of `when' . . . not `if' . . . variant B.1.1.7 becomes dominant in Denmark.
Although there are some officials and researchers worried that the 501Y.V2 variant may be the bigger threat, for now it appears to be lagging behind B.1.1.7 in spreading globally.
That could change, of course, depending on how well the current vaccines work against one (or hopefully both) of these variants. And any that follow.
While I remain cautiously optimistic, we should be prepared for a long haul, as SARS-CoV-2 is unlikely to go quietly into the night.
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