Reinfection, reactivation of SARS-CoV-2 and false negatives in final reports can be possible reasons
As the whole world puts up a collective fight against the novel coronavirus disease (COVID-19) pandemic, some worrying news has cropped up from across Asia — patients who tested negative of the disease are getting infected with the virus (SARS-CoV-2) again.
Such cases have been reported from South Korea, China and Japan. Three probable explanations are being proffered to explain the trend.
The first explanation suggests that patients who tested negative are being reinfected. This is unusual as people who have already contracted the disease build antibodies against the pathogen that offers protection for at least some time.
Researchers from China addressed the possibility of reinfection by conducting experiments on rhesus monkeys. They infected four monkeys with SARS-CoV-2 and monitored their viral loads. After 28 days, they found that the oral and anal swabs of monkeys did not show the presence of the virus.
At this point, the team tried to reinfect the animals, but was unable to do so. The study was published on the preprint server bioRxiv on March 13, 2020. The researchers concluded that the findings could help in development of vaccines against the virus.
However, this might not be that simple.
As of now, we have no idea how long the immunity from the disease can last. In case of common cold — also caused by members of the coronavirus family — resistance is provided only for a few months.
A review of available information on this subject by the Norwegian Institute of Public Health found very limited evidence on immunity after infection with SARS-CoV-2.
“Two studies showed sustainable immunoglobulin (igG) levels one to two years after SARS-CoV infection, but it is uncertain whether this finding can be generalised to SARS-CoV-2. It is also uncertain whether sustained levels of antibodies will provide full protection against reinfection,” the document published in April 2020 stated.
Researchers at the School of Basic Medical Sciences, Fudan University, Shanghai studied blood samples from patients who had been released after treatment and found that nearly a third had low levels of antibodies. In some patients, the antibodies could not be detected at all.
The titers (concentration) of antibodies varied according to age. Older patients had more antibodies than the younger ones.
The study was published in medRxiv on March 30, 2020 and has not been peer-reviewed.
This could mean that if the real virus cannot induce an antibody response, the weakened version used in a vaccine may not work.
The second reason offered on the front was reactivation of the virus in some patients.
South Korea’s Centre for Disease Control (CDC) claimed the virus reactivated in some patients. It said it would study this further.
“The most likely explanation is that people have simmering virus replication for an unusually long time and this can occasionally result in late reactivation. Most available data stated that the length of virus detection varies from person to person, so it isn’t surprising that some people might continue to produce the virus and get sick,” says Dave O’ Connor, professor at the Department of Pathology and Laboratory Medicine, University of Wisconsin-Madison.
This explanation, too, is worrisome as this could possibly mean that herd immunity would not work against the pandemic.
The third possibility is the tests declaring the patients to be free of the virus are giving false negative reactions. This means that other than improving diagnostic tests, there is a need to improve sampling techniques.
“It is not known for sure what is happening, but it is likely that the virus is still growing at some site in the body, perhaps the lower lung or intestines, which is harder to sample and is giving a false negative for the virus,” said Benjamin Neuman, professor of biological sciences at Texas A&M University, Texas.
However, it could also be that patients are testing positive because of residual viral ribonucleic acid in their bodies.
In the Chinese city of Shenzhen, researchers found that 38 of 262 patients tested positive after they were discharged from hospitals. People they came in contact with did not test positive for the virus. The study was published on the preprint server Medrxiv on March 26, 2020.
A long-term research is the only hope to clear the air. Such numbers are messing with the exisiting data. The uncertainty needs to be kept in mind while developing vaccines and diagnostics for COVID-19.
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