New Study Finds Natural and Vaccine-Induced Immunity Will Shape Future Trajectory of Coronavirus Pandemic

Researchers from the Princeton University (Princeton, NJ, USA) used a simple model to project the future incidence of COVID-19 cases - and the degree of immunity in the human population - under a range of assumptions related to how likely individuals are to transmit the virus in different contexts. For example, the model allows for different durations of immunity after infection, as well as different extents of protection from reinfection. The researchers posted online an interactive version of model’s predictions under these different sets of assumptions. As expected, the model found that the initial pandemic peak is largely independent of immunity because most people are susceptible. However, a substantial range of epidemic patterns are possible as SARS-CoV-2 infection - and thus immunity - increases in the population.

The nature of the immune responses also can affect clinical outcomes and the burden of severe cases requiring hospitalization, the researchers found. The key question is the severity of subsequent infections in comparison to primary ones. Importantly, the study found that in all scenarios a vaccine capable of eliciting a strong immune response could substantially reduce future caseloads. Even a vaccine that only offers partial protection against secondary transmission could generate major benefits if widely deployed, the researchers reported.

The study authors also explored the effect of “vaccine hesitancy” on future infection dynamics. Their model found that people who decline to partake in pharmaceutical and non-pharmaceutical measures to contain the coronavirus could nonetheless slow containment of the virus even if a vaccine is available. One of the main takeaways of the study was that monitoring population-level immunity to SARS-CoV-2, in addition to active infections, will be critical for accurately predicting future incidence.

“Much of the discussion so far related to the future trajectory of COVID-19 has rightly been focused on the effects of seasonality and non-pharmaceutical interventions (NPIs), such as mask-wearing and physical distancing,” said co-first author Chadi Saad-Roy, a Ph.D. candidate in Princeton’s Lewis-Sigler Institute for Integrative Genomics. “In the short term, and during the pandemic phase, NPIs are the key determinant of case burdens. However, the role of immunity will become increasingly important as we look into the future.”

“Ultimately, we don’t know what the strength or duration of natural immunity to SARS-CoV-2 - or a potential vaccine - will look like,” added co-first author Caroline Wagner, an assistant professor of bioengineering at McGill University who worked on the study as a postdoctoral research associate in the Princeton Environmental Institute (PEI). “For instance, if re-infection is possible, what does a person’s immune response to their previous infection do? Is that immune response capable of stopping you from transmitting the infection to others? These will all impact the dynamics of future outbreaks.”

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