Understanding whether and how recovery from COVID-19 confers immunity to, or decreased severity of, reinfection is needed to inform current efforts to safely scale back population-based interventions, such as physical distancing. This viewpoint describes what is currently known about the immune response to COVID-19, highlight key gaps in knowledge and opportunities for future research.
Main findings include:
- Following infection, detectable IgM and IgG antibodies develop within days to weeks of symptom onset in most infected individuals, but it is not clear why some patients do not develop this humoral immune response.
- A small study of 9 patients with COVID-19 found that greater clinical severity produced higher antibody titers; however, antibody detection and higher titers have not always been found to correlate with clinical improvement in COVID-19. Moreover, mild COVID-19 symptoms can resolve prior to seroconversion.
- Viral burden typically peaks early in illness. The absolute duration that a patient might shed infectious virus is unknown.
- The durability of neutralizing antibodies (NAbs, primarily IgG) against SARS-CoV-2 has yet to be defined. Data from other coronaviruses indicate that antibody responses could persist for up to 36 months, however, it remains to be determined whether a robust IgG response corresponds with immunity.
- To date, no human reinfections with SARS-CoV-2 have been confirmed.
In summary, limited data on antibody responses to SARS-CoV-2 and related coronaviruses, as well as one small animal model study, suggest that recovery from COVID-19 might confer immunity against reinfection, at least temporarily. However, the immune response to COVID-19 is not yet fully understood and definitive data on postinfection immunity are lacking.