The persistence of SARS-CoV-2 antibodies in COVID-19 patients at least three months after symptom onset was reported in two separate studies late last week in the journal Science Immunology.
Both studies indicate that longer-lasting immunoglobulin G (IgG) antibodies may hold promise as a means for assessing the viral immune response. One research also shows a link between the levels of blood and saliva antibodies, indicating that saliva may act as an alternative to blood testing that is easier to obtain.
Although in infected patients, the existence of COVID-19-specific antibodies, immune molecules produced by the body in response to a virus, has been demonstrated the durability of COVID-19 antibodies is not yet fully known. Prior studies in asymptomatic patients have shown antibodies reducing to undetectable levels 2 months after infection.
The period of antibody response is important for controlling the dissemination of COVID-19 and for guiding the production of vaccines.
In the first new study, researchers measured antibodies specific to the receptor-binding domain of the SARS-CoV-2 spike protein in the blood of 343 patients for up to 122 days after onset of symptoms, comparing antibody levels with those of 1,548 pre-pandemic sampled individuals.
The study authors found that IgG, along with protective neutralizing antibodies, was elevated in patients for four months, with immunoglobulin A and M (IgA and IgM) antibodies comparatively short-lived, both decreasing to low levels about 2.5 months after symptom onset. In particular, IgG levels were highly successful in detecting patients with symptoms for at least 14 days, indicating a role for IgG identification of positive cases of missing polymerase chain reaction (PCR) monitoring, which continues to decrease over time in sensitivity.
The second study showed a similar period of antibody response in 402 COVID-19 patients at the University of Toronto Hospital whose antibody responses were reported 3 to 115 days after onset. Their reactions were compared by researchers with those of 339 pre-pandemic control patients.
IgA and IgM antibodies were shown to have decayed quickly, while IgG antibodies remained remarkably stable for up to 105 days after symptom onset.
The investigators have observed a strong link between blood and saliva levels of antibodies.
Neither research lasted beyond four months, restricting the opportunity to draw conclusions on sustained immunity, but both provide optimism that reinfection defense could be established by people infected with the virus.
Recognizing the remaining knowledge gaps in antibody duration and the degree of protection provided against reinfection, the authors of the Toronto study point to the potential for a durable vaccine antibody response.
"This study suggests that if a vaccine is properly designed, it has the potential to induce a durable antibody response that can help protect the vaccinated person against the virus that causes COVID-19," Jennifer Gommerman, Ph.D., of the University of Toronto wrote in a university press release.
