Recovered COVID-19 patients retain broad and effective longer-term immunity to the disease, suggests a recent Emory University study, which is the most comprehensive of its kind so far. The findings have implications for expanding understanding about human immune memory as well as future vaccine development for coronaviruses.
The longitudinal study, published recently on Cell Reports Medicine, looked at 254 patients with mostly mild to moderate symptoms of SARS-CoV-2 infection over a period for more than eight months (250 days) and found that their immune response to the virus remained durable and strong.
Emory Vaccine Center director Rafi Ahmed, PhD, and a lead author on the paper, says the findings are reassuring, especially given early reports during the pandemic that protective neutralizing antibodies did not last in COVID-19 patients.
“The study serves as a framework to define and predict long-lived immunity to SARS-CoV-2 after natural infection. We also saw indications in this phase that natural immunity could continue to persist,” Ahmed says. The research team will continue to evaluate this cohort over the next few years.
Researchers found that not only did the immune response increase with disease severity, but also with each decade of age regardless of disease severity, suggesting that there are additional unknown factors influencing age-related differences in COVID-19 responses.
In following the patients for months, researchers got a more nuanced view of how the immune system responds to COVID-19 infection. The picture that emerges indicates that the body’s defense shield not only produces an array of neutralizing antibodies but activates certain T and B cells to establish immune memory, offering more sustained defenses against reinfection.
“We saw that antibody responses, especially IgG antibodies, were not only durable in the vast majority of patients but decayed at a slower rate than previously estimated, which suggests that patients are generating longer-lived plasma cells that can neutralize the SARS-CoV-2 spike protein.”
Ahmed says investigators were surprised to see that convalescent participants also displayed increased immunity against common human coronaviruses as well as SARS-CoV-1, a close relative of the current coronavirus. The study suggests that patients who survived COVID-19 are likely to also possess protective immunity even against some SARS-CoV-2 variants.
“Vaccines that target other parts of the virus rather than just the spike protein may be more helpful in containing infection as SARS-CoV-2 variants overtake the prevailing strains,” says Ahmed. “This could pave the way for us to design vaccines that address multiple coronaviruses.”
Researchers say the study more comprehensively identifies the adaptive immune components leading to recovery, and that it will serve as a benchmark for immune memory induced by SARS-CoV-2 vaccines. “We can build on these results to define the progression to long-lived immunity against the new coronavirus, which can guide rational responses when future outbreaks occur,” says Ahmed.
The study, funded by multiple institutions including the National Institutes of Health, is a collaboration between Emory University and the Fred Hutchinson Cancer Research Center in Seattle, Washington.