In a study published back in May, researchers at the University of Amsterdam determined that the general population remains defended against SARS-CoV-2 for a period of six months after viral clearance. This estimation has been challenged many times since–perhaps most notably by a paper published in the Clinical Infectious Disease journal.
The authors reviewed a 33-year-old man who developed characteristic COVID-19 symptoms in March (cough, sore throat, fever, and headache), tested positive for the novel coronavirus, recovered, and then tested positive again in mid-August.
Similar reports out of the UK indicated that detectable coronavirus antibodies decreased by roughly 27% over a period of three months this past summer.
“Antibody positivity was greater in those who reported a positive PCR and lower in older people and those with asymptomatic infection. These data suggest the possibility of decreasing population immunity and increasing risk of reinfection as detectable antibodies decline in the population,” the authors wrote in the new paper published on Monday.
Coronavirus antibodies likely function differently between patient samples though they’re not the only instructive measures regarding our humoral immune response. T-cell memory additionally plays a monumental role.
Memory T cells are geared to recognize specific antigens. When they encounter said antigens again upon re-exposure to a virus they will enact a faster and stronger immune response.
“Declining antibody levels after the acute infection has resolved is the sign of a normal healthy immune response,” Dr.Scott Hensley, who is an immunologist at the University of Pennsylvania said in a statement to the New York Times. “It doesn’t mean that those people no longer have antibodies. It doesn’t mean that they don’t have protection.”
It should be noted that assessing antibody levels in a given community only says so much about individual protection against a pathogen. Partly because age and pre-existing conditions further dictate analysis on this front.
If we’re talking about young, otherwise healthy populations? Research seems to support the theory that coronavirus antibodies remain stable for several months.
Ania Wajnberg, an associate professor at the Icahn School of Medicine, Mount Sinai produced new research in line with this projection.
The Mount Sinai Health System started screening coronavirus patients for antibodies back in March. Some later volunteered to contribute to convalescent plasma therapy.
In order to determine the longevity of the participant’s antibody response, the researchers examined 121 plasma donors, all of which evidenced stable antibody titers for a period of about five months. Dr.Wajnberg and colleagues soon recorded their data in the paper linked above.
“SARS-CoV-2 has caused a global pandemic with millions infected and numerous fatalities. Questions regarding the robustness, functionality, and longevity of the antibody response to the virus remain unanswered. Here we report that the vast majority of infected individuals with mild-to-moderate COVID-19 experience robust IgG antibody responses against the viral spike protein, based on a dataset of 30,082 individuals screened at Mount Sinai Health System in New York City,” the authors wrote in the new paper. “Titers are relatively stable for at least a period approximating 5 months and that anti-spike binding titers significantly correlate with neutralization of authentic SARS-CoV-2. “
The majority of stable antibodies came from mild and asymptomatic cases. This is important, because the majority of COVID-19 cases can be classified as either and because both cohorts contribute the most to national outbreaks.
“Our data suggests that more than 90% of seroconverters make detectible neutralizing antibody responses. These titers remain relatively stable for several months after infection,” the authors added.
There are outliers that defy continuous immunity data so even those who have already contracted COVID-19 need to exercise caution. It is also not entirely known how transmissibility is affected by SARS-CoV-2 antibody levels.