One study has found that people who have contracted SARS-CoV-2 are immune to the virus for at least 5 to 7 months and probably live longer.
Recent alleged cases of resorption with SARS-CoV-2, the coronovirus that causes COVID-19, have raised concerns that the human immune system may only provide short-term protection against the virus.
In addition, rare research has suggested that the number of antibodies in a person’s bloodstream that is capable of inactivating the virus declines rapidly after initial infection.
However, scientists at the University of Arizona (Urijona) College of Medicine in Tucson have now found evidence of long-lasting immunity in people who have COVID-19.
He tested for the presence of antibodies to the virus in about 6,000 individuals and then followed them for several months.
“We clearly see high-quality antibodies, which are still occurring 5 to 7 months after SARS-CoV-2 infection,” Dr. Associate Professor of Immunobiology at the university. Says Deepa Bhattacharya, who co-led the research.
“Many concerns have been expressed about immunity against COVID-19 which is not sustainable. We used this study to investigate that question and found that immunity is stable for at least 5 months. ”
Bhattacharya explains that those who contracted the SARS-COV virus responsible for the 2002–2004 outbreak of SARS were immunized even 12–17 years after infection. This virus is similar to SARS-CoV-2.
“If SARS-CoV-2 is anything like the first one, we expect the antibody to last for at least 2 years, and it is unlikely to be very low,” he says.
In his letter, published in the magazine ImmunityScientists also noted that out of nearly 30 million cases of COVID-19 since December 2019, only 10 confirmed cases have been confirmed.
Researchers began recruiting volunteers for trials on April 20, 2020 in Pima County, AZ.
The main objective of the research was to develop an accurate antibody blood test that can identify individuals who have contracted the virus.
Existing tests that screen for antibodies against a single target on the virus particle produce plenty of “false positives”. This means that some people who have never contracted the virus will test positive.
To get around this problem, scientists developed a test that first looks for antibodies to a target on the virus. If the test detects them, the samples are tested for antibodies to another target.
A person will test positive only if they have antibodies to both targets.
One target of the new test is the receptor-binding domain, or RBD, which is part of the virus’s spike protein that it uses to invade host cells. The other target is another segment of the spike called S2.
To confirm how well the test works, the researchers incubated plasma samples with live viruses in a high-security laboratory. They then exposed the cell cultures to the mixture that the antibodies in the samples neutralized the virus.
These investigations showed that only one test out of 5,882 gave a false-positive result. In other words, if a population was examined, less than 0.02% of tests would falsely indicate that someone had contracted the virus.
In August 2020, the Food and Drug Administration (FDA) granted a new test “Emergency Use Authority.” As a result, Bhattacharya and his team have now tested approximately 30,000 people in Arizona.
Scientists have also kept an eye on how long the virus’s immunity remains in people who initially tested positive.
This showed that the level of immunity was the strongest among those who experienced the most severe infections. However, immune strength did not appear to vary by age or sex.
In addition, their research showed that after an initial decline, immune levels stabilized and remained for at least 5 to 7 months of follow-up.
“Whether antibodies provide permanent protection against SARS-COV-2 has been one of the most difficult questions to answer. This research has not only given us the ability to properly test antibodies to COVID-19, but has also equipped us with the knowledge that permanent immunity is a reality. ”
– Dr. Michael D. Dey, co-author and senior vice president, Urijona Health Sciences
Other studies have suggested that immunity is short-term, in particular, in people with mild infections.
The authors of the new study believe that these studies made the mistake of maintaining immunity for a long time, neutralizing antibodies.
They write 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, the following form long-lived antibody-producing cells, which can last for years.
“Thus, the decay in antibody production after infection or vaccination is not linear and cannot be done beyond initial time, demonstrating the need for early follow-up studies,” they write.
The authors note two limitations of their study. First, they state that there is a possibility that people who contracted the virus lost their immunity before taking an antibody test and, therefore, tested negative.
Secondly, maximum follow-up was done 226 days after the onset of the disease. There is a possibility that antibody levels may decrease rapidly thereafter.
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