Is a person infected with the coronavirus contagious even after Covid disease has healed? And from now on, a persistent infection gives the patient immunity? Virologists worldwide are currently discussing this question. This was triggered by four cases which, after surviving Covid disease and initially negative tests, were tested positive again for the virus.
Even if the SARS CoV-2 coronavirus continues to spread, new infections are only half the story. Because the majority of the more than 90,000 Covid cases listed worldwide have since recovered from the infection – among them are primarily the people who had contracted SARS-CoV-2 in January. The World Health Organization WHO currently lists more than 48,000 recovered patients.
What Happens After Covid Disease?
In general, doctors assume that people who have no symptoms for several days and who have been tested negative in virus tests have survived the infection. However, the PCR test (polymerase chain reaction) used for this does not detect the intact virus, but rather reacts to fragments of the virus genome in the samples. The result of these tests is therefore typically negative if there are no more viruses in the body.
But even without such a test, most virologists estimate that the risk of infection from healthy patients is rather low: “It is assumed that if someone has survived the disease, antibodies have formed and the virus no longer reproduces in the body”, explains Isabella Eckerle, virologist at the Geneva University Hospital. So far, therefore, Covid patients have been discharged as healed after their symptoms have ended and, after a safety buffer of a few days, they generally no longer have to keep in quarantine.
Tested positive again despite recovery
However, at the end of February 2020, a scientific publication from China caused a sensation – it seemed to contradict the common picture of a cured infection. Physicians led by Lan Lan from Zhongnan Hospital in Wuhan reported four Covid patients who had tested negative for SARS-CoV-2 twice a day after the symptoms had subsided.
When the PCR test was repeated after five to 13 days, the values were positive again. However, there were no new symptoms in these patients. This report raises the question of whether the coronavirus may still be present in cured patients – and whether these patients may still be contagious.
No evidence of continued risk of infection
This fear is now contradicted by several virologists and infectious medicine experts: “What is detected with the PCR test is not the virus, but the virus genome. However, viral RNA can often still be detected long after the infectious virus has disappeared, ”explains Florian Krammer from Mount Sinai Hospital in New York. “This happens with measles, but also with Zika and Ebola.”
According to the expert, such viral genetic remains are most likely also responsible for the alleged flare-up of the infection in the four Chinese patients. Isabella Eckerle, virologist at the University Clinic in Geneva, has a similar view: “As long as the virus remains, the test remains positive, even though the virus may no longer be infectious,” she explains. She therefore assumes that the positive test results in these patients recovering from Covid-19 are not a sign of persistent infection or any further risk of infection. Krammer sees it similarly.
Are you immune after surviving infection?
Another question currently under discussion is immunity: are patients protected against a new infection after surviving Covid disease? “We already have data that Covid 19 patients form antibodies after being infected with the virus,” reports Eckerle. Similar to the flu or measles, the immune system of those affected is protected against further infection with the same virus.
“We therefore assume that patients who have had a coronavirus infection will develop immunity to the virus,” says Eckerle. This was also observed with the closely related viruses SARS and MERS-CoV. However, it is currently unclear how long this immunity will last. “If you assume an analogy to the other corona viruses, you could assume a period of a few years: With SARS, for example, antibodies are detectable for three to five years,” says the virologist.
No signs of a mutation (yet)
Such immune protection requires, however, that the virus does not mutate in the meantime. So far, however, there are no signs of this. According to a WHO report, 104 different isolates of the coronavirus SARS-CoV-2 are known to date, which were taken and analyzed between December 2019 and February 2020. The genome of these viruses was 99.9 percent identical, so there is no evidence of a significant mutation, according to the WHO report.
However, it cannot be ruled out that the corona virus could still mutate in the course of its global spread. This could lead to a further increase in transferability and a change in the severity of the course of the disease – for example because the virus adapts even better to human cells. So far, however, there are no signs of this.
New infections in China are declining
And one more thing is hopeful: In China, the drastic measures to contain the epidemic seem to be slowly taking effect. The number of new cases every day has dropped from almost 2,000 a day in the beginning to only around 200, as the WHO reports. Although the number of infections continues to increase in South Korea, there is no evidence of any further expansion of the outbreak zones: “The cases there seem to come mainly from the five known clusters, not from the general population,” said WHO Director General Tedros Adhanom Ghebreyesus.
According to the WHO, this is an indication that a quick response and quarantine can help to at least slow down, possibly even stop, the spread of SARS-CoV-2. “If this were an influenza pandemic, we would expect widespread transmission to people around the world,” says Ghebreyesus. But that doesn’t seem to be the case so far.
“Our message to all countries is: we can suppress this virus. Your actions will determine the course of the outbreak in your country, ”said the WHO Director General. However, there are many epidemiologists who are already talking about a pandemic and who no longer consider it possible to contain the coronavirus. Those who are right will have to show themselves.
Source: WHO, Nature, SMC, Robert Koch Institute, JAMA, doi: 10.1001 / jama.2020.2783
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