When you become infected with the flu and then recover, your immune system develops antibodies that, in most cases, prevent you from getting infected a second time. This does not mean that you can’t become sick again– there are four different strains of the flu- but at the very least you shouldn’t become re-infected with the same strain again .
When the COVID-19 pandemic began, researchers found high levels of antibodies in the blood of recovered patients, providing a glimmer of hope that immunity would at least be granted to those who have already been infected. After all, antibodies are one of the reasons blood transfusion therapy was approved by the FDA and used earlier this month in an American hospital.
Coronavirus Patients Testing Positive for a Second Time
Troubling news, however, is coming out of South Korea and China, where patients who were thought to have recovered from COVID-19 are being readmitted to hospital after testing positive for a second time .
Since the news broke, South Korean officials have announced 111 cases of re-infection . The Korean Centers for Disease Control and Prevention (KCDC) has released a statement that they will be conducting a formal investigation into the patients who have tested positive for a second time .
Similar cases have been reported in Wuhan, China, where the outbreak is thought to have originated.
The World Health Organization is also investigating the cases.
“We are aware of these reports of individuals who have tested negative for COVID-19 using PCR (polymerase chain reaction) testing and then after some days testing positive again,” said the organization. “We are closely liaising with our clinical experts and working hard to get more information on those individual cases. It is important to make sure that when samples are collected for testing on suspected patients, procedures are followed properly.” 
A patient can be discharged from the hospital only after receiving two consecutive negative results that are twenty-four hours apart, according to WHO guidelines .
Can You be Re-Infected with COVID-19?
While these reports sound alarming, it may not actually be that patients are getting re-infected, but rather had a lingering infection that was not detected by tests for a period of time. A second positive test could be a false-negative, meaning that the patient is still infected.
David Hui, a respiratory medicine expert at the Chinese University of Hong Kong who also studied the 2002-2003 outbreak of severe acute respiratory syndrome (SARS), explains how this could happen:
“It may be because of the quality of the specimen that they took and may be because the test was not so sensitive,” he said .
Vineet Menachery, a virologist at the University of Texas Medical Branch, says that a positive test after recovery could also be detecting residual RNA of the virus that is still present in the body, but not in amounts high enough to cause infection.
“Viral RNA can last a long time even after the actual virus has been stopped,” he explained .
Oh Myoung-don, a professor of internal medicine at Seoul National University and a member of the WHO’s Strategic and Technical Advisory Group for Infectious Hazards, agrees that this is the likely cause.
“Even after the virus is dead, the nucleic acid (RNA) fragments still remain in the cells,” says Oh .
What Does This Mean?
Because COVID-19 is so new, there is still much we do not know about how the virus acts, how it spreads, and how long it can linger in the body once someone has been infected.
“As COVID-19 is a new disease, we need more epidemiological data to draw any conclusions of virus shedding profile,” the WHO said .
As for immunity, researchers cannot say for certain whether having the virus once will protect you from getting it again in the future. Since there hasn’t yet been enough time to study COVID-19, experts are using information from other members of the coronavirus family, such as SARS and MERS, to make predictions about what will happen with the new virus.
Hsu Li Yang, an associate professor, and infectious disease expert at the National University of Singapore warns that we are barely four months into this pandemic, so many uncertainties remain.
“The comments we’re making are based on previous knowledge of other human coronavirus and SARS. But whether they extrapolate across COVID-19, we’re not so sure at present.” 
Current estimates suggest that COVID-19 antibodies could stay in the blood of a recovered patient for up to two or three years based on data from other coronaviruses, but again, it is too early to make any definitive claims.
“We would expect that if you have antibodies that neutralize the virus, you will have immunity,” Menachery says. “How long the antibodies last is still in question.” 
As medical researchers continue to study the virus and learn more about its behavior, more information will become available as to how to prevent another pandemic from happening again in the future.
In the meantime, however, the best we can do is to continue practicing social distancing, washing our hands thoroughly, and following the direction from health officials, in order to lessen the burden on our healthcare system and get control over this outbreak.
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