The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the infectious agent of the coronavirus disease 2019 (COVID-19), continues to spread worldwide.
A large number of patients with COVID-19 have recovered. In some cases, however, people test positive for SARS-CoV-2 again or experience a recurrence of clinical symptoms. To fully understand this baffling aspect of the pandemic, further research is required.
Reasons for re-infection
Re-infection means that a person was infected once, has recovered, and then later became infected again.
The study, which was published in the journal New Microbes and New Infections, focused on the possible reasons for positive retesting, antibody responses, and a review of potential re-infection case reports.
Some scientists believe that a positive retest is tied to the long-term persistence of the virus in the body. In some studies, re-infections are attributed to the reverse transcription-polymerase chain reaction (RT -PCR) false-negative results at discharge, long term viral shedding, and increased virus replication due to drug discontinuation.
If re-infection is true, controlling the pandemic will be very complicated, and herd immunity to the vaccine may be difficult to achieve.
SARS-CoV-2 re-infection has not been fully explained, but several reports show people testing positive again after two consecutive negative PCR tests or after recovery from the illness.
Prolonged viral shedding
It is crucial to differentiate between prolonged viral shedding or reactivation and true re-infection.
A true re-infection should meet these criteria, including isolation of the complete viral genome and not just fragments in the second infection. In some cases, detection of viral genomic fragments may lead to a positive PCR test result.
Viral shedding in the upper respiratory tract may also take as long as 83 days. If a person has tested positive after this period, it can be confirmed as a re-infection.
Further, scientists have also hypothesized that the gastrointestinal tract might act as a reservoir for SARS-CoV-2 even after test samples from the upper respiratory tract come out negative.
The team also recommends testing stool specimens at the time of discharge.
Antibody responses in patients with COVID- 19
The immune system works by protecting the body against pathogens. Humoral immune responses are the first line of defense against re-infection.
The immune responses against COVID-19 are still unclear. In one study, the overall seroconversion rate was 96.8 percent. In a separate study, the seroconversion was 100 percent by 39 days after the onset of infection.
Other reports showed that the body produces antibodies for at last four months, protecting against re-infection.
The first reported re-infections occurred in South Korea in April, but it took until August 24 before a case was officially confirmed. A 33-year-old man treated in Hong Kong for mild illness in March tested positive again when he returned from Spain on August 15.
In a similar case in the United States, a patient was reinfected 140 days after a primary infection. The first infection happened in March, and he had a second bout in July, where he had a cough, weakness, and difficulty breathing. The genomic analysis showed that the viral strains isolated in the two episodes were not the same.
Some researchers believe that retesting positive for COVID-19 may be explained by the infection's reactivation or relapse.
"Retest positive for SARS-CoV-2 should be interpreted correctly because there are several reasons, such as false-negative test results at discharge, prolonged shedding of the virus, virus replication's rebound after drug discontinuation and re-infection," the researchers explained.
The researchers also emphasized that though re-infection may occur, the incidence is very low.
The ongoing pandemic
Of the 57 million cases of COVID-19 worldwide, 36.63 million have already recovered. The pandemic has also claimed more than 1.36 million lives.