Properly Designed COVID-19 Vaccine Can Induce Durable Antibody Response to SARS-CoV-2, Finds Studies

The researchers used both saliva and blood samples from COVID-19 patients to measure and compare antibody levels for over three months post-symptom onset. They found that antibodies of the IgG class that bind to the SARS-CoV-2 spike protein are detectable for at least 115 days, representing the longest time interval measured. The study is also the first to show these antibodies can also be detected in the saliva. While the team admits there is a lot they still don’t know about antibody responses to SARS-CoV-2 infection, including how long the antibodies last beyond this period or what protection they afford against re-infection, the research could have broader implications in the development of an effective vaccine.

“Our study shows that IgG antibodies against the spike protein of the virus are relatively durable in both blood and saliva,” said Jennifer Gommerman, professor of immunology in U of T’s Temerty Faculty of Medicine and leader of the saliva testing effort. “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.”

The study led by the Toronto team was in agreement with findings from leading immunologists in the US in describing the antibody response as longer lasting. In the second study, researchers in Boston, US used enzyme-linked immunosorbent assay (ELISA) to measure the antibody responses of 343 COVID-19 patients up to 122 days after symptom onset. The researchers then compared the measurements to prepandemic blood sample controls. The team found that spike protein-specific IgM and IgA antibodies were short-lived, falling to lower than detection levels at around 49 and 71 days, respectively, after the appearance of symptoms. On the other hand, the spike protein-targeted IgG responses decayed more slowly, with just three patients losing them within 90 days after the appearance of symptoms. The researchers also found no cross-reactivity of antibodies to SARS-CoV-2 RBD with widely circulating common cold coronaviruses, demonstrating the specificity of the assay.

"These data suggest that RBD-targeted antibodies are excellent markers of previous and recent infection, that differential isotype measurements can help distinguish between recent and older infections, and that IgG responses persist over the first few months after infection and are highly correlated with neutralizing antibodies," noted author Anita Iyer, PhD, of Massachusetts General Hospital and Harvard Medical School and colleagues.

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University of Toronto
Lunenfeld-Tanenbaum Research Institute