April 12-18 2021
Large-scale vaccination: the best protection against the UK variant
The UK variant of SARS-CoV-2, detected for the first time in the south of England in September 2020, spread rapidly through the country and became the dominant strain. It has now been detected in more than 114 countries across the globe. This variant is characterized by 14 mutations and 3 deletions, of which 8 are in the spike surface protein. At least 3 mutations seem to impact on the virus’ functioning. The N501Y mutation provides better affinity for the ACE2 cellular receptor which facilitates entry of the virus into the cell. The P681H mutation could play a significant role in the virus’ capacities for infection and transmission. And the 69-70 deletion may be linked to immune system evasion and increases in infectivity. Researchers at the School of Hygiene and Tropical Medicine in London have worked to better understand why this virus seems to spread faster than other strains. They wanted to estimate the severity of illness linked to this new variant and to evaluate the levels of preventative public health measures necessary to slow its spread.
First of all they estimated the virus’ rate of transmission using data from cases in the United Kingdom, Denmark, Switzerland and the United States. Using mathematical modelling, they found that this new variant may be 43 to 90% more transmissible than the original strain.
In order to better understand the mechanics of this increase in transmissibility, they analysed possible changes in social contact between individuals. However, any such modifications of social behaviour did not seem sufficient to explain this increase in the virus’ transmissibility.
The researchers did not identify differences in the severity of the illness linked to this variant, unlike a previous study (see letter News-COVID-19.info March 22-28 2021), although their results need to be validated.
Finally, the researchers simulated the epidemic’s momentum between December 2020 and June 2021, taking into account differences in public health measures and vaccination levels. Although their research dates back to last year, it is clear that their projections are now largely confirmed.
In their initial projections they predicted a new wave of cases and deaths in 2021, with the proviso that mortality rates could be reduced by the implementation of strict public health measures. In the absence of significant deployment of vaccination, the number of hospitalizations and deaths in 6 months was expected to be higher than in 2020, regardless of health measures. According to them, if vaccination levels reached only 200 000 people per week, its impact would be limited. On the other hand, if the vaccination campaign accelerated and reached 2 000 000 per week, the impact on hospitalisations and deaths would be much greater.
This can be represented as:
In conclusion, these researchers showed that the spread of the UK variant was more rapid than with the original strain. The epidemic’s momentum risks being similar to that seen with variants that have emerged in South Africa and in Brazil. The authorities in the UK responded quickly to the appearance of the new variant, by closing schools from the 5th of January 2021. But it is above all the vaccination campaign, leading to the rapid attainment of herd immunity, that has limited the new wave of deaths.