Long-term containment of COVID-19 will be determined by the strength and duration of immunity

New research suggests that the impact of natural and vaccine-induced immunity will be key factors in shaping the future trajectory of the global coronavirus pandemic, known as COVID-19. In particular, a vaccine capable of eliciting a strong immune response could substantially reduce the future burden of infection, according to a study by Princeton researchers published in the journal. Sciences September 21st. Credit: Tumisu from Pixabay

New research suggests that the impact of natural and vaccine-induced immunity will be key factors in shaping the future trajectory of the global coronavirus pandemic, known as COVID-19. In particular, a vaccine capable of eliciting a strong immune response could substantially reduce the future burden of infection, according to a study by Princeton researchers published in the journal. Sciences September 21st.

“Much of the discussion thus far related to the future trajectory of COVID-19 has correctly focused on the effects of seasonality and non-pharmaceutical interventions. [NPIs]such as the use of masks and physical distancing, “said co-first author Chadi Saad-Roy, a doctoral candidate at the Lewis-Sigler Institute for Integrative Genomics at Princeton.” In the short term and during the pandemic phase, ISFLs are the key determinant of the caseload. However, the role of immunity will become increasingly important as we look to the future. “

“Ultimately, we don’t know what the strength or duration of natural immunity to SARS-CoV-2, or a possible vaccine, will be like,” explained co-first author Caroline Wagner, assistant professor of bioengineering at McGill University, who He worked on the study as a postdoctoral research associate at the Princeton Environmental Institute (PEI).

“For example, if reinfection is possible, what does a person’s immune response do to their previous infection?” Wagner asked. “Is that immune response capable of preventing you from transmitting the infection to others? All of this will affect the dynamics of future outbreaks.”

The current study is based on Princeton research published in Sciences May 18 reporting that local variations in climate are unlikely to dominate the first wave of the COVID-19 pandemic and included many of the same authors, all affiliated with PEI’s initiative on climate change and infectious diseases.

In the most recent article, the researchers used a simple model to project the future incidence of COVID-19 cases, and the degree of immunity in the human population, under a variety of assumptions related to the likelihood that individuals will transmit the virus. in different countries. contexts. For example, the model allows for different durations of immunity after infection, as well as different degrees of protection against reinfection. The researchers published online an interactive version of the model’s predictions under these different sets of assumptions.

As expected, the model found that the initial pandemic spike is largely independent of immunity because most people are susceptible. However, it is possible that a wide range of epidemic patterns exists as SARS-CoV-2 infection and thus immunity in the population increases.

“If immune responses are only weak or transiently protective against reinfection, for example, larger and more frequent outbreaks can be expected in the medium term,” said co-author Andrea Graham, professor of ecology and evolutionary biology at Princeton.

The nature of immune responses can also affect clinical outcomes and the burden of severe cases requiring hospitalization, the researchers found. The key question is the severity of the later infections compared to the primary ones.

Importantly, the study found that, in all scenarios, a vaccine capable of eliciting a strong immune response could substantially reduce the number of future cases. Even a vaccine that offers only partial protection against secondary transmission could yield significant benefits if widely implemented, the researchers reported.

Factors such as age and over-propagation events are known to influence the spread of SARS-CoV-2 by causing individuals within a population to experience different immune responses or to transmit the virus at different rates. “Our models show that these factors do not affect our qualitative projections about the future dynamics of the epidemic,” said Bryan Grenfell, the Kathryn Briger and Sarah Fenton Professor of Ecology and Evolutionary Biology and Public Affairs and an associate faculty member at PEI. Grenfell is co-lead author of the paper with C. Jessica Metcalf, associate professor of ecology and evolutionary biology and public affairs and also a member of the PEI associate faculty.

“As vaccine candidates emerge, and more detailed predictions of future vaccination cases are needed, these additional details will need to be incorporated into more complex models,” Grenfell said.

The study authors also explored the effect of “vaccine vacillation” on the dynamics of future infection. Their model found that people who refuse to participate in pharmaceutical and non-pharmaceutical measures to contain the coronavirus could nonetheless delay containment of the virus even if a vaccine is available.

“Our model indicates that if vaccine rejection is high and correlated with increased transmission and riskier behavior, such as refusing to wear a mask, then the vaccination rate required to achieve herd immunity could be much higher.” said co-author Simon Levin, the James S. McDonnell Distinguished University Professor in Ecology and Evolutionary Biology and an associate faculty member at PEI. “In this case, the nature of the immune response after infection or vaccination would be very important factors in determining how effective a vaccine would be.”

“When there is so much uncertainty in the underlying processes, it can be challenging to make accurate projections about the future,” Grenfell said. “We argue in this study that ultimately a family of both simpler and more complex models is the best way to proceed under these circumstances. Carefully compare the predictions of these models and then obtain a carefully averaged picture of the future, as with prediction. time: it can be very useful. “

One of the main conclusions of the study is that monitoring the population’s immunity to SARS-CoV-2, in addition to active infections, will be essential to accurately predict future incidence.

“This is not an easy thing to do with precision, particularly when the nature of this immune response is not well understood,” said co-author Michael Mina, an assistant professor at the Harvard School of Public Health and Harvard Medical School. “Even if we can measure a clinical amount as an antibody titer against this virus, we don’t necessarily know what that means in terms of protection.”

“Studying the effects of T-cell immunity and cross-protection from other coronaviruses are important avenues for future work,” Metcalf said.

The document entitled “History of immune life, vaccination and dynamics of SARS-CoV-2 during the next five years” was published online by Sciences September 21st.