French Study Confirms That SARS-CoV-2 New Variants Possess Higher Transmissibility Capabilities And Have A Longer Infectious Period!
A new study by French researchers from Université de Montpellier, Cerba Laboratory-Saint Ouen L’Aumône, Laboratoire de Virologie-CHU de Montpellier and Université de Paris have found that SARS-CoV-2 new variants
possess higher transmissibility capabilities and have a longer infectious period. The study covered the B.1.1.7, P1 and B.1.351 variants.
First Author, Dr Baptiste Elie from the Université de Montpellier said in the study abstract, “SARS-CoV-2 variants are causing epidemic rebounds in many countries. By analyzing longitudinal cycle threshold (Ct) values from screening tests in the general population and hospitals, we found that infections caused by variant lineages have higher peak viral load than wild type lineages and, for the B.1.1.7 lineage, have a longer infectious period duration. Linking within-host kinetics to transmission data suggests that infections caused by variants have higher transmission potentials and that their epidemiological fitness may depend on the demography of the host population.”
The study findings were published on a preprint server and are currently being peer reviewed. https://www.medrxiv.org/content/10.1101/2021.05.26.21257835v1
The study team analyzed data on three variants of concern and found that viral loads were higher and infection lasted longer for the B.1.1.7 variant. They all were more infectious than the original strain, and transmissibility also depended on population demographics.
The SARS-CoV-2 coronavirus has evolved since it first emerged in late 2019. Several mutations of the virus have since been observed, with some variants appearing more infectious than the original strain, which also appear to evade immunity gained by previous infections.
Importantly some of these variants have been labeled as variants of concern (VOC) because of their greater transmissibility and infectiousness. These have also been associated with second and third waves in the infections in many countries, leading to their close monitoring, either by sequencing the complete viral genome or reverse-transcription polymerase chain reaction (RT-PCR).
Certain RT-PCR studies have suggested that the VOCs may be causing higher viral loads, but those studies were done only at one-time point.
However in this new study, the study team reports how different variants affect virus kinetics in infections.
The team used data from RT-PCR tests specific to variants performed between February and April 2021 on SARS-CoV-2 positive samples. They used data from more than 17,000 samples. About 73% of the samples were of the B.1.1.7 variant, 6% of the B.1.351 or P.1 variants, and the rest were wild-type.
A detailed model was developed that included several co-factors, such as the patient's age, the virus lineage, and whether the patient was hospitalized.
The study team found that the viral loads were different between the wild-type virus and the different variants. For the B.1.1.7 strain, peak virus load increased with age. The cycle threshold values for the B.1.351 and P.1 strains were slightly lower than that for the wild-type strain, i
ndicating slightly lower viral loads for these variants.
Furthermore the rate of decrease of viral load with time was lower for the B.1.1.7 strain compared to the wild-type virus. The data also showed higher peak loads and a lower rate of viral load decrease in hospitalized individuals, about 1.5 days more.
Importantly there was a significant correlation between the cycle threshold value and the decrease in viral loads, suggesting a linear relationship between the cycle threshold value and infectiousness. These researchers found there was a greater risk of transmission for variants than for wild-type viruses.
It was found that for the B.1.1.7 strain, greater transmission was more evident in countries with an older population like Japan (a median advantage of 41%) and France. In contrast, for the B.1.351 and P.1 variants were more evident for countries with a younger population like Niger (median advantage of 26%).
Hence the analysis shows the SARS-CoV-2 variants have a higher potential of transmission, which also depends on the population's demographics.
The study team suggests future studies should look at combing the cycle threshold data and the serological data to understand how the B.1.351 and P.1 variants escape our immune response.
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