Delta-like SARS-CoV-2 variants will most likely increase the severity of the pandemic


Transmission electron micrograph of SARS-CoV-2 virus particles, isolated from a patient. The image was taken and color enhanced at the NIAID Integrated Research Facility (IRF) in Fort Detrick, Maryland. Credit: NIAID

A SARS-CoV-2 variant with properties similar to the Delta variant – improved transmissibility and an ability to infect people who have had previous infections / vaccinations – will cause a more serious pandemic with more infections and breakthrough infections / reinfections than variants with either property alone according to a mathematical model created by researchers at the Harvard TH Chan School of Public Health.

Their work, which was published online November 19, 2021 in Cell, could help researchers and public health officials interpret the meaning of new and existing variants and design tailored public health responses to different scenarios based on a variant’s characteristics.

“So far, evidence of immune flight – a variant’s ability to evade the immune system and cause re-infections or breakthrough infections – has been a red flag,” said Mary Bushman, co-author of the Cell paper and a postdoc researcher in the Department of Epidemiology at Harvard Chan School. . “Our results say it may be more of a yellow flag – this is not that big in itself. But when combined with improved portability, it can be a really big deal.”

As the COVID pandemic has progressed, variants of the original wild-type SARS-CoV-2 virus have emerged. Some have quickly become a dominant strain and increased the number of infections, such as the Alpha and Delta variants, while others, such as Beta, failed to address or significantly affect the trajectory of the pandemic. To understand the effects that certain factors would have on a pandemic, Bushman created a model that simulates how pandemics driven by hypothetical variants would affect populations using different combinations of masking with physical distancing and vaccinations.

The analysis simulated a SARS-CoV-2 pandemic with several different hypothetical variants including combinations of the two features: improved transmissibility, similar to the Alpha variant; partial immune escape, similar to the Beta variant; improved transferability with partial immununescape, similar to the Delta variant; and a variant without any properties. The analysis also took into account how certain variables, such as masking / physical distancing or vaccinations, would affect the course of the pandemic. For each of the scenarios, the researchers analyzed the total number of infections as well as the number / percentage of infections averted by vaccination.

Bushman and their team determined that a variant with increased transmissibility alone would likely be more dangerous than a variant that could partially evade the immune system. Yet a variant with both properties can cause more infections, reinfections and breakthrough infections than a variant with both properties alone.

According to the model, vaccination is also predicted to be extremely beneficial in the case of Delta-like variants, because vaccinations would prevent a greater number of cases that a more transmissible virus would potentially cause, and because the milder nature of breakthrough infections would significantly reduce overall mortality.

“It’s really important that people realize the emergence of variants like Delta makes high levels of vaccination even more crucial,” said Bill Hanage, associate professor of epidemiology and co-author of the Cell paper. “Although we can not remove the virus, we can ensure that people face it with the best preparation, and a more transmissible virus means that there will be more infections in the absence of vaccination, so more people can benefit from it. ”

Other co-authors from Harvard Chan School for the study included Rebecca Kahn, Bradford Taylor and Marc Lipsitch.

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More information:
Mary Bushman et al., Population exposure of SARS-CoV-2 variants with improved transmissibility and / or partial immune release, Cell (2021). DOI: 10.1016 / j.cell.2021.11.026

Journal information:

Provided by Harvard TH Chan School of Public Health

Citation: Delta-like SARS-CoV-2 variants will most likely increase the severity of the pandemic (2021, November 19) retrieved November 20, 2021 from cov- variants-pandemic-severity.html

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