Coronavirus antibodies can last for at least three months following a person getting infected with SARS-CoV-2, the virus that causes COVID-19, according to two studies published in Science Immunology.
Scientists from the University of Toronto and the Lunenfeld-Tanenbaum Research Institute at Sinai Health used both blood samples and saliva from coronavirus patients to assess and compare antibody levels for over three months post the onset of the first symptom.
They detected that antibodies of the immunoglobulin G (IgG) class that bind to the virus spike protein are detectable for around 115 days.
This is also the first study to demonstrate that these antibodies can also be identified in saliva.
Another study, from Harvard Medical School, reported similar findings. This means that a properly designed vaccine "should elicit a durable antibody response that has the potential to neutralise the virus," said Jen Gommerman of the University of Toronto, co-author of the study.
Her group also found that antibodies in saliva correlated with antibodies in blood, but at this point, the saliva tests are not sensitive enough to replace blood tests.
The two studies, together involving nearly 750 patients, both point to IgG antibodies, which start showing up well after an infection begins, as the longest-lasting.
Researchers found IgG antibodies with two targets - a spike protein on the virus that helps it infect cells, and a part of the spike called the receptor binding domain (RBD) - lasted more than 100 days.
While the protective effect of Covid-19 antibodies is not completely clear, Gommerman said her team also found levels of so-called neutralising antibodies, which inactivate the virus, "appeared to be very stable."
Covid-19 symptoms linger for months for many
Three months after becoming ill, many Covid-19 patients still have symptoms, two studies confirm, and the more severe the initial infections, the higher the odds of persistent problems. In Spain, doctors checked back with 108 patients, including 44 who had been severely ill.
At 12 weeks after diagnosis, 76% still reported after-effects, with 40% reporting three or more coronavirus-related health issues, doctors said in a paper posted on Thursday on medRxiv ahead of peer review.
The most common complaints were shortness of breath, physical weakness, cough, chest pain, palpitations, and psychological and cognitive disorders.
In a similar study of 233 US Covid-19 patients - eight of whom had been severely ill - one in four still had symptoms 90 days after first feeling ill.
Rates were higher for patients who had been sicker: 59.4% at 30 days and 40.6% at 90 days. "But even for very mild and initially asymptomatic cases, 14.3% has complications persist for 30 days or longer," the authors reported on Sunday on medRxiv.
In the US study, the most common persistent symptoms were impaired smell and taste, difficulty concentrating, shortness of breath, memory loss, confusion, headache, heart palpitations, chest pain, pain with deep breaths, dizziness, and rapid heartbeat.
(With inputs from Reuters)