Mathematical Model Shows How SARS-CoV-2 Variants Could Affect Pandemic Trajectory

A SARS-CoV-2 variant with traits similar to those of the Delta variant, such as enhanced transmissibility and an ability to infect people who had previous infections/vaccinations, will cause a more severe pandemic with more infections than variants with either trait alone, according to results of a mathematical model by Harvard T.H. Chan School of Public Health.

The model could help researchers and public health officials interpret the significance of existing variants and design tailored public health responses for various scenarios based on a variant’s characteristic.

The findings were published in Cell.

“Thus far, evidence of immune escape—the ability of a variant to evade the immune system and cause reinfections or breakthrough infections—has been a red flag,” said Mary Bushman a postdoctoral research fellow in the department of epidemiology at Harvard Chan School, in a statement. “Our findings say it’s maybe more of a yellow flag—this is not such a big deal on its own. But when it’s combined with enhanced transmissibility, then it can be a really big deal.”

The researchers determined that the variant with enhanced transmissibility would be more dangerous than a variant that could partially evade the immune system. However, a variant with both traits could cause more infections, reinfections, and breakthrough infections than a variant with either trait alone, according to the study.

They also found that vaccination is predicted to be highly beneficial in the case of Delta-like variants because it would prevent a greater number of cases that a more transmissible virus would cause and because the milder nature of breakthrough infections should substantially reduce overall mortality.

With the progression of the pandemic, COVID-19 variants have emerged, but not all of the variants have affected the trajectory of the pandemic, such as the Beta variants. However, some have become more dominate strains, like the Alpha and Delta variants.

The analysis showed several different hypothetical variants, including combinations of traits associated with the Alpha, Beta, and Delta variants: enhanced transmissibility, partial immune escape, enhanced transmissibility and partial immune escape, respectively, and variants with neither trait, according to the study authors.

Additionally, the analysis factored in how variables, such as masking, social distancing, and vaccinations, would affect the COVID-19 pandemic’s trajectory.

For each scenario, the researchers analyzed the total number of infections as well as the number and percentage of infections adverted by vaccination.

Reference

Delta-like SARS-CoV-2 variants are most likely to increase pandemic severity. EurekAlert. News release. November 19, 2021. Accessed November 22, 2021. https://www.eurekalert.org/news-releases/935615