Studies Show Lasting Immune Responses to COVID-19, Even in Mild Cases

Encouraging results from several studies on immune responses to SARS-CoV-2 show persistent antibody reactivity to the virus, even in those who developed only mild symptoms. Questions about immunity duration and reinfection remain, but an influx of new research suggests that antibodies appear to persist months after infections have resolved.

A longitudinal assessment from researchers at the University of Washington, pre-printed on medRxiv and in a paper under review by the journal Nature, looked at “immune memory” for SARS-CoV-2 in 15 recovered patients who had mild cases. Plasma and peripheral blood mononuclear cells were collected 20 days after a positive polymerase chain reaction test and a median 35.5 days post symptom onset. Researchers found that recovered individuals developed SARS-CoV-2-specific IgG antibody and neutralizing plasma, as well as virus-specific memory B and T cells that persisted, and in some cases increased, over 3 months following symptoms.

Marion Pepper, PhD, an author of the University of Washington study, said that protection against reinfection cannot be fully confirmed until there is unambiguous data that those who encounter the virus a second time are protected, but the new findings are promising.

A study from Harvard Medical School and Massachusetts General Hospital, also pre-printed on medRxiv, measured antibody responses to the receptor-binding domain (RBD) of the spike (S) protein of SARS-CoV-2 in 259 patients with symptomatic COVID-19, compared to 1,548 blood samples obtained prior to the pandemic. Most SARS-CoV-2 positive cases included were severe (95% of patients were hospitalized, 31% required ICU level care, and 16% died). Between 14 and 28 days from the onset of symptoms, participants with COVID-19 showed robust IgG, IgA, or IgM antibody responses to RBD. LgA and lgM antibody responses reduced by 51 and 47 days post-symptoms, while lgG antibodies persisted through 75 days.

However, a research team in Hong Kong recently discovered a potential case of COVID-19 reinfection months after initial infection – raising questions about the durability of immune response.

Other studies, looking at mucosal and systemic antibody responses, T cell immunity, and humoral responses to COVID-19 have also been pre-published online in recent weeks.

Sources: The New York Times, August 17, 2020; Rodda LB, Netland J, Shehata L, et al. Functional SARS-CoV-2-specific immune memory persists after mild COVID-19. medRxiv preprint. August 15, 2020; Iyer AS, Jones FK, Nodoushani A, et al. Dynamics and significance of the antibody response to SARS-CoV-2 infection. medRxiv preprint. July 20, 2020.