People who have recovered from COVID-19 infection remain immune to the virus for at least five to seven months or more, as the body still produces high quality antibodies against the virus, a new research has revealed.
The study, carried out by scientists at the University of Arizona College of Medicine, United States, was published in Immunity, a monthly peer-reviewed medical journal of immunology.
According to Medical News Today, before now, there have been alleged cases of re-infection with COVID-19, which have raised concerns that the human immune system may only provide short-term protection.
The publication also noted that a ‘Scarce Research’ had suggested that the number of antibodies in a person’s bloodstream that is capable of disabling the COVID-19 virus declines sharply after an initial infection.
According to the researchers, while carrying out the experiment, about 6000 individuals were tested for the presence of antibodies to the virus, and were followed up for several months.
One of the lead authors, Dr. Deepta Bhattacharya, an associate professor of immunobiology, said during the research, “We clearly see high quality antibodies still being produced five to six months after COVID-19 infection.
“Many concerns have been expressed about immunity against COVID-19 not lasting.
“We used this study to investigate that question and found immunity is stable for at least 5 months.”
Bhattacharya pointed out that people who contracted the SARS-CoV virus, responsible for the 2002 to 2004 SARS outbreak, still had immunity for 12 to 17 years after infection, stressing that the virus is very similar to that of COVID-19.
He noted that out of nearly 30 million cases of confirmed infection with COVID-19 since December 2019, there have only been about 10 confirmed cases of reinfection.
“If SARS-CoV-2 is anything like the first one, we expect antibodies to last at least 2 years, and it would be unlikely for anything much shorter,” he added.
The researchers revealed that they began recruiting volunteers for the research in Pima County, Arizona, on April 20, 2020.
They explained that the main objective of the research was to develop an accurate antibody blood test that could identify individuals who have contracted the virus.
Existing tests that screen for antibodies against a single target on the virus particle tend to produce a lot of “false positives”, the researchers noted, adding that it means that some people who have never contracted the virus would test positive.
Medical News Today, explained that in order to get around this problem, the scientists developed a test that first looked for antibodies to one target on the virus, and that once the test detects them, the sample is then screened for antibodies to another target.
A person will only test positive if they have antibodies to both targets, the publication noted.
It pointed out that one target of the new test is the receptor-binding domain, or RBD, which is the part of the virus spike protein, which it uses to invade host cells.
The other, it further said, is another section of the spike protein called S2.
To confirm how well the test worked, the researchers explained that they incubated plasma samples with the live virus in a high security lab, and later exposed the cell cultures to the mixture to see whether antibodies in the samples had neutralized the virus.
They said checks revealed that only one test out of 5,882 gave a false-positive result.
“In other words, if a population were screened, fewer than 0.02 per cent of tests would falsely indicate that someone had contracted the virus,” they observed.
It was noted that based on the report, in August 2020, the Food and Drug Administration, gave the new test an “emergency use authorization”, and that it had made Bhattacharya and his team test nearly 30,000 people in Arizona.
The scientists revealed that they have also tracked how long immunity to the virus lasted among those who initially tested positive.
They revealed that the result showed that levels of immunity were strongest among those who experienced the most severe infections, but that the strength of immunity did not appear to vary according to age or sex.
In addition, their research showed that after an initial decline, levels of immunity stabilized and persisted for at least five to seven months of the follow-up.
The researchers noted that other studies have suggested that immunity is short lived, in particular, among those with mild infections, and that such studies made the mistake of extrapolating long-term immunity from the early falls they saw in neutralizing antibodies.
They pointed out that in a typical viral infection, there is an initial wave of short-lived antibody-producing immune cells, which then quickly decline in number.
“However, what follows is the creation of a smaller number of longer lived antibody-producing cells, which can last for years.
“Thus, the decay in antibody production after infection or vaccination is not linear and can’t be extrapolated from early time points, demonstrating the need for longer-term follow-up studies,” they stated.
The authors, however, noted two limitations in their study; the first being that there is a possibility that some individuals who had contracted the virus lost their immunity before they took the antibody test and, therefore, tested negative.
The second one is that the maximum follow-up was 226 days after the onset of the disease, noting that there remains a possibility that antibody levels may decline sharply thereafter.