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 recently published in the journal Science.
“The current study builds on previous research which reported that local variations in climate are not likely to dominate the first wave of the Covid-19 pandemic,” said study authors from McGill University in Canada.
In the most recent paper, 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 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.
“If immune responses are only weak, or transiently protective against reinfection, for example, then larger and more frequent outbreaks can be expected in the medium term,” said co-author Andrea Graham from Princeton University.
The nature of the immune responses also can affect clinical outcomes and the burden of severe cases requiring hospitalization, the researchers found.
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.
“Our model indicates that if vaccine refusal is high and correlated with increased transmission and riskier behaviour such as refusing to wear a mask, then the necessary vaccination rate needed to reach herd immunity could be much higher,” they wrote.