People who have recovered from COVID-19 retain broad and effective longer-term immunity to the disease, according to a new study.
Findings of the study, which is the most comprehensive of its kind so far, have implications for expanding understanding about human immune memory as well as future vaccine development for coronaviruses.
For the longitudinal study in Cell Reports Medicine, researchers looked at 254 patients with mostly mild to moderate symptoms of SARS-CoV-2 infection over a period of more than eight months (250 days) and found that their immune response to the virus remained durable and strong.
The findings are reassuring, especially given early reports during the pandemic that protective neutralizing antibodies didn’t last in COVID-19 patients, said Rafi Ahmed, director of the Emory University Vaccine Center and a lead author of the paper.
“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 said.
The research team will continue to evaluate this cohort over the next few years.
The 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 said 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,” Ahmed said. “This could pave the way for us to design vaccines that address multiple coronaviruses.”
The researchers said 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,” Ahmed said.
The National Institutes of Health funded the work, which is a collaboration between Emory University and the Fred Hutchinson Cancer Research Center in Seattle, Washington.