Scientists, including one of Indian origin, have documented the persistence of antibodies that attack the new coronavirus in the blood and saliva of Covid-19 patients at least three months after the onset of symptoms, a finding that may lead to methods alternative tests for viral infection.
The study, published in the journal Science, points to the class of IgG antibodies as the longest-lasting antibodies detectable in patients during this time period, and they may serve as promising targets for detecting and evaluating immune responses against SARS-CoV. -two. virus.
Follow the latest updates on the Covid-19 pandemic here
According to researchers, including those at Harvard Medical School in the US, these antibodies could be detected at similar levels in both blood and saliva, suggesting that saliva could be used as an alternative biofluid for antibody testing. .
In the research, Anita Iyer and her team measured the antibody responses in the blood of 343 Covid-19 patients up to 122 days after the onset of symptoms, and compared these responses with those of 1,548 control individuals sampled before the pandemic. .
The scientists focused only on antibodies specific to the receptor-binding domain of the SARS-CoV-2 spike protein that it uses to enter host cells.
They estimated the sensitivities of IgG, IgA, and IgM antibody types at 95%, 90%, and 81%, respectively, to detect infected individuals between 15 and 28 weeks after the onset of symptoms.
Among these antibodies, the study noted that spike protein-specific IgM and IgA were short-lived, falling below detection levels around 49 and 71 days, respectively, after onset of symptoms.
However, he noted that IgG responses targeting spike proteins slowly declined over a 90-day period, and only three people lost them within this time period.
Also read: What is special about bat viruses? What we don’t know can hurt us
According to the researchers, spike protein-specific IgG levels strongly correlated with neutralizing antibody levels in patients.
They also did not observe cross-reactivity of any antibodies directed against SARS-CoV-2 with other “common cold” coronaviruses.
Another study published in the journal Science also found that while IgA and IgM antibodies directed at the receptor-binding domain of the spike protein declined rapidly, the IgG type remained relatively stable up to 105 days after onset of symptoms in 402 patients with Covid-19.
In this study, researchers such as Baweleta Isho of the University of Toronto in Canada, detected spike protein specific antibodies in the saliva, as well as in the blood, of these patients.
They plotted the patients’ antibody responses from 3 to 115 days after the onset of symptoms and compared their profiles with 339 pre-pandemic controls.
The scientists found that Covid-19 patients showed peak IgG levels between 16 and 30 days after the onset of symptoms.
According to the researchers, the levels of all spike protein-specific IgG, IgM and IgA antibodies in the blood were positively correlated with the levels seen in matching saliva samples.
“Since the virus can also be measured in saliva by PCR, the use of saliva as a biofluid for virus and antibody measurements may have some diagnostic value,” they wrote in the study.
.
