COVID-19 induces lasting humoral immunity

After symptomatic coronavirus disease 2019 (COVID-19), the body is able to sustain humoral immunity against SARS-CoV-2, a recent study has found.

Through immunoassays and neutralization assays, the researchers measured immunoglobulin M (IgM) and G (IgG) antibodies against the virus’ spike (S) protein receptor binding domain (RBD), as well as neutralizing antibodies, 6 months after symptomatic disease onset in 349 patients. The participants contributed a total of 585 samples.

Within the first week of symptom onset, IgM and IgG against the S protein had positivity rates of 67 percent and 11 percent, respectively. The same antibodies against the virus nucleocapsid (N) protein were detected in 33 percent and 22 percent, respectively.

Notably, IgG-S became detectable in 98 percent of patients by week 3 and remained at relatively high frequencies all throughout the observation, lasting until 26 weeks after symptom onset. A similar effect was reported for IgG-N, which rose to 88 percent frequency by week 2, staying relatively stable until the end of the analysis.

Notably, IgMs against the S and N proteins jump immediately in response to the virus, but recede just as quickly, reaching undetectable levels by 12 weeks.

In terms of disease control, IgM and IgG levels were significantly higher in patients in whom SARS-CoV-2 RNA was no longer detectable. Similarly, IgG responses against the S and N proteins were also heightened in patients with nonsevere COVID-19. Together, these results suggest a clinically relevant protective effect of antibodies against the virus.

Neutralization assays also showed that at 2 weeks post-onset, half of the patients produced antibodies capable of neutralizing the virus. By week 4, this proportion rose to 90 percent, remaining high until week 26.