COVID-19 antibodies found to persist at least three months
Two separate studies late last week in Science Immunology document the persistence of SARS-CoV-2 antibodies in COVID-19 patients at least three months after symptom onset, according to a report from University of Minnesota's Center for Infectious Disease Research and Policy, which publishes CIDRAP News.
Both studies suggest that longer-lasting immunoglobulin G (IgG) antibodies may hold promise as a tool to evaluate viral immune response. One study also demonstrates a correlation between blood and saliva antibody levels, suggesting that saliva could serve as an easier-to-collect alternative to blood testing.
While the presence of COVID-19–specific antibodies—immune molecules generated by the body in response to a virus—has been demonstrated in infected patients, the durability of COVID-19 antibodies is not yet fully understood. Previous studies have shown antibodies diminishing to undetectable levels two months after infection in asymptomatic patients.
The duration of antibody response is critical for tracking the spread of COVID-19 as well as to inform vaccine development.
In the first new study, researchers measured antibodies specific to the SARS-CoV-2 spike protein's receptor binding domain in the blood of 343 patients for up to 122 days after symptom onset, comparing antibody levels to those of 1,548 individuals sampled before the pandemic.
The study authors found that IgG was elevated in patients for 4 months along with protective neutralizing antibodies, with immunoglobulin A and M (IgA and IgM) antibodies relatively short-lived in comparison—both declining to low levels around 2.5 months after symptom onset. Notably, IgG levels were highly effective in identifying patients who had symptoms for at least 14 days, suggesting a role for IgG detection of positive cases missed by polymerase chain reaction (PCR) testing, which tends to wane in sensitivity over time.
The second study found a similar duration of antibody response among 402 University of Toronto Hospital COVID-19 patients whose antibody responses were recorded from 3 to 115 days after onset. Researchers compared their responses with those from 339 pre-pandemic control patients. They found that IgA and IgM antibodies rapidly decayed, while IgG antibodies remained relatively stable for up to 105 days after symptom onset.
The authors also found a positive correlation between antibody levels in blood and saliva. "Given that the virus can also be measured in saliva by PCR, using saliva as a biofluid for both virus and antibody measurements may have some diagnostic value," the study authors said in news release from the American Association for the Advancement of Science, which publishes the journal.
