Calculating the Success of COVID Booster Shots

Mathematical model predicts long-term effectiveness in different patient populations

Photo illustration of a syringe and a bottle marked "COVID vaccine"
Image: MicroPixieStock/iStock/Getty Images Plus

This article is part of Harvard Medical School’s continuing coverage of COVID-19.

Researchers have designed a mathematical model that can predict the course of vaccine-induced immunity against COVID-19 in different patient populations — including otherwise healthy individuals and those who have cancer or suppressed immune responses — over the long term.

The model, developed by a team led by Harvard Medical School investigators at Massachusetts General Hospital, in collaboration with scientists at the University of Cyprus, also makes predictions under potential future scenarios, such as the emergence of SARS-CoV-2 variants with greater immune evasion, and reveals the benefits of the new bivalent vaccines.

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The model builds on the investigators’ previously developed mathematical framework that they used to understand why treatment responses vary widely among people with COVID-19 and to identify biological markers related to these different responses, published in PNAS in 2021.

In this latest work, also published in PNAS, the scientists addressed the need for predictions of vaccine effectiveness over time.

“We used this model to simulate how differences in viral, patient, and vaccine characteristics may affect COVID-19 outcomes,” said senior author Rakesh Jain, the A. Werk Cook Professor of Radiation Oncology at HMS and director of the Edwin L. Steele Laboratories for Tumor Biology at Mass General.

For example, the model incorporates different variants of SARS-CoV-2 (including hypothetical ones), original and bivalent forms of the vaccine, and different considerations for certain patients, such as interactions between the virus, immune cells, and tumor cells in individuals with cancer.

The model predicted that a booster dose of either the Pfizer-BioNTech or Moderna mRNA vaccines can induce robustly enhanced antibody- and immune cell-based responses against SARS-CoV-2 to provide sufficient protection for more than one year in healthy individuals.

However, the model suggested that for people with suppressed immune responses or those with cancer who are receiving immunosuppressive treatments, the booster effect may wane fairly quickly. These patients should therefore be given booster vaccines more frequently than others.