UK SARS-CoV-2 variant 40% more transmissible than previous strains

Japanese researchers have estimated that the B.1.1.7 variant strain of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that recently emerged in England is 40% more transmissible than strains that previously circulated in the country.

The SARS-CoV-2 virus is the causative agent of the 2019 coronavirus disease pandemic (COVID-19) which continues to pose a significant threat to global public health and has now claimed more than 2.68 million deaths in the world.

The researchers say that the estimated 40% higher transmissibility of B.1.1.7 suggests that the measures implemented to control this strain need to be increased by 40%, compared to those used to control previously circulating strains.

For equivalent control effects to be achieved, contact rates between individuals should be less than 0.71 of the rates obtained using previous measurements.

Chayada Piantham and Kimihito Ito of Hokkaido University warn that the transmissibility benefit of other recently emerged strains such as those identified in Brazil and southern Arica also needs to be urgently assessed.

A pre-printed version of the research paper is available on the medRxiv* server, while the article is subject to peer review.

Number of sequences in England from September 1, 2020 to February 19, 2021. Nucleotide sequences were extracted from GISAID on March 1, 2020.

What do we know so far about the B.1.1.7 lineage?

Since the start of the COVID-19 epidemic in Wuhan, China in late December 2019, the rapid spread and evolution of the causative agent SARS-CoV-2 has led to the emergence of new variants that present a transmission advantage over the original strain.

In December 2020, Public Health England identified a new cluster of viruses belonging to the B.1.1.7 lineage, which the World Health Organization called a “Variant of Concern” due to its increased transmissibility, compared to strains that previously circulated in England.

Since the line was first identified in the country in September 2020, the number of infections with this new strain has increased rapidly in October and November. As of February 2021, B.1.1.7 viruses accounted for 95% of all strains of SARS-CoV-2 circulating in England.

Previous studies assumed that the number of spawners is constant over time

Several studies have compared the number of reproduction (R; number of secondary infections resulting from a single infection) of the B.1.1.7 line to that of strains previously circulating in England.

A study estimated that the R The number of strain B.1.1.7 is between 83 and 118% higher than that of the previous strains, while another study estimated that it was between 40 and 75% higher.

The methods used in these studies estimated the increase in transmissibility under the assumption that R is constant over time during the target analysis period.

However, since the increased transmissibility of the B.1.1.7 lineage was recognized, strict control measures, including lockdown, have been imposed in England.

“So the constant R The hypothesis is debatable when analyzing the increase in reproduction number of B.1.1.7 compared to that of previously circulating strains, ”say Piantham and Ito.

What did the researchers do?

The team estimated the selective advantage of the B.1.1.7 line over previous strains using the time course of the B.1.1.7 virus fraction identified in England.

Based on the Wallinga-Teunis method for estimating instantaneous reproduction numbers, the approach allowed the reproduction number to change during the target period of the analysis.

The approach was also based on a Maynard Smith model, which assumes that the selective advantage of a mutant strain over previously circulating strains is constant over time.

Researchers downloaded nucleotide sequence data on SARS-CoV-2 viruses detected in England from the EpiCoV database GISAID (Global Initiative on Sharing Avian Influenza Data) on 1^st March 2021.

The team then applied the new method to estimate the instantaneous reproduction number of B.1.1.7 strains, compared to that of previously circulating strains.

What did they find?

The researchers estimated that the selective advantage of the B.1.1.7 strains over the non-B.1.1.7 strains was 0.40, indicating that the instantaneous reproduction number of the B.1.1.7 line was 40%. higher than that of previous strains. .

This suggests that the control measures used to contain the B.1.1.7 line need to be stepped up by 40%, compared to those used to control previous strains, the team explains.

For the equivalent control effect to be achieved, contact rates between individuals should be limited to less than 0.71 of the rates obtained with the measures previously used.

The selective advantage of new strains in other countries should also be assessed

The team emphasizes that from the 17th^e In March 2021, the B.1.1.7 line was detected in 93 countries.

“The selective advantage of B.1.1.7 strains over strains previously circulating in other countries remains to be our future work,” say the researchers.

In addition, Piantham and Ito point out that the variants identified in Brazil and South Africa also exhibit higher transmissibility than previous strains.

“It is also urgent to estimate the selective advantage of these strains”, they conclude.

*Important Notice

medRxiv publishes preliminary scientific reports which are not peer reviewed and, therefore, should not be considered conclusive, guide clinical practice / health-related behaviors, or treated as established information.