A SARS-CoV-2 variant with traits similar to that of the Delta variant—enhanced transmissibility and an ability to infect people who had previous infections/vaccination—will cause a more severe pandemic with more infections and breakthrough infections/reinfections than variants with either trait alone, according to a mathematical model created by researchers at Harvard T.H.

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

As the COVID pandemic has progressed, variants of the initial wild-type SARS-CoV-2 virus have emerged.

Some have quickly become a dominant strain and increased the number of infections, like the Alpha and Delta variants, while others, like Beta, failed to take hold or significantly affect the pandemic’s trajectory.

The analysis simulated a SARS-CoV-2 pandemic with several different hypothetical variants including combinations of the two traits: enhanced transmissibility, similar to the Alpha variant; partial immune escape, similar to the Beta variant; enhanced transmissibility with partial immune escape, similar to the Delta variant; and a variant with neither trait.

Bushman and their team determined that a variant with enhanced transmissibility alone would likely be more dangerous than a variant that could partially evade the immune system.

Yet a variant with both traits could cause more infections, reinfections, and breakthrough infections than a variant with either trait alone. .

According to the model, vaccination is also predicted to be highly 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 should substantially reduce overall mortality. .

“It’s really important that people realize the emergence of variants like Delta make high levels of vaccination all the more crucial,” said Bill Hanage, associate professor of epidemiology and co-author of the Cell paper.

Reference: “Population impact of SARS-CoV-2 variants with enhanced transmissibility and/or partial immune escape” by Mary Bushman, Rebecca Kahn, Bradford P.

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