So far, people who have survived Covid-19 disease have been considered protected: their immune system protects them from being infected again with Sars-CoV-2 – this is the common assumption. But now a case in Hong Kong raises doubts. Because a young man contracted the corona virus again just five months after his first infection. Genetic analyzes showed that the second infection took place with a different variant of Sars-CoV-2 – it cannot therefore be a recurrence of the first infection.
In the case of many infectious diseases, the initial contact with a pathogen causes our immune system to remember the “enemy”: memory cells store protein signatures of the virus, for example, and release large amounts of antibodies when they come into contact with the pathogen again. In the ideal case, these dock precisely to key structures in the virus envelope and thus prevent the virus from multiplying. As a result, the second infection is warded off – we are immune. This immune memory forms the basis for all active vaccinations – including the candidates currently being developed against Sars-CoV-2. But with this new coronavirus in particular, it is still unclear how good and lasting the immune protection is after an infection has been overcome. Theoretically, it would be possible that a Covid-19 disease that has passed through protects against re-infection for months or even years, but it could also be that there is only partial protection through which you can be infected again, but no longer difficult ill.
So far, there has been little data that provides clear evidence of continued immune protection after Covid-19 – but also no clear counter-evidence. In March 2020, doctors in China had already reported some cases in which patients had repeatedly tested negative for Sars-CoV-2 after the symptoms had subsided. However, five to 13 days later, her tests for Sars-CoV-2 were positive again. At the time, however, these cases were not considered sufficient evidence of re-infection. Because, in the opinion of many scientists, the short time interval between the illness and a new test suggested that the positive tests no longer detected infectious residues of the coronavirus or that the tests that were negative in the meantime were false negative. This was supported by the fact that the symptoms flared up again in some of these cases – apparently their Covid 19 disease was not yet completely healed.
Five months after recovering from Covid-19, positive again
The situation is different with the current case from Hong Kong. This is a 33-year-old man who went to the doctor in mid-March 2020 with a cough, fever, headache and sore throat and tested positive for Sars-CoV-2 on March 26th. On April 14th, he was discharged from Hong Kong hospital as healthy after two negative PCR tests. On August 15, 2020, however, the man returned to Hong Kong from a trip to Spain and had a routine smear test for Sars-CoV-2 at the airport. The test was positive, although the person did not show any symptoms. The patient was nevertheless admitted to the hospital as a precaution and was thoroughly examined and monitored. There tests confirmed the presence of an acute coronavirus infection: “The patient had increased reactive C-protein in the blood, a relatively high viral load and developed IgG antibodies against Sars-CoV-2 in the course of the infection,” report Kelvin Kai-Wang To and his colleagues. However, the patient did not develop a fever and there were no typical changes in his lungs.
This could mean that this man could have contracted Sars-CoV-2 again just five months after he survived Covid-19. In order to be absolutely sure that it was not a latent infection and thus an aftereffect of the first infection, the researchers carried out comparative genetic analyzes. They compared the genetic makeup of the virus currently isolated from this patient with that of the samples taken in March. “The analyzes showed that the first viral genome belonged to a different strain of Sars-CoV-2 than the second,” the scientists report. Accordingly, when the man was first infected in March, he was infected with a variant of the virus that was widespread in England and the USA at the time. The coronaviruses isolated from his smear in August, on the other hand, were of a variant that was circulating in Switzerland and England at the time.
Clear evidence of re-infection?
According to the researchers, these data show that their case is a real re-infection. Other scientists, including Jeffrey Barrett of the Wellcome Sanger Institute in Great Britain, see it similarly: “This is certainly stronger evidence of re-infection than some of the earlier reports, because here the gene sequence of the virus is used to differentiate the two infections ”He comments. If this is confirmed, then, in the opinion of To and his colleagues, this could have an impact on the further course of the pandemic, but also on the vaccinations: “The confirmation of the re-infection has several important implications: On the one hand, it is unlikely that herd immunity Sars-CoV-2 can eliminate ”, they write. “On the other hand, vaccines will probably not be able to provide lifelong protection against Covid-19.”
However, other researchers are critical of these conclusions: “Given that we only know one case so far, I think their conclusions are far too broad,” says Barrett. Paul Hunter of the University of East Anglia sees it similarly: “The importance of this case should not be overemphasized. Because it is very likely that subsequent infections will not cause as serious a disease as the first because there is still partial immunity, ”said the doctor. Therefore, in his opinion, even a partially effective vaccine could still protect enough to prevent severe courses. “We need more information about this case and more cases of re-infection before we really understand the implications,” says Hunter. The technical article by To and colleagues is so far only available in excerpts and has not yet been assessed by a peer review. Parts of the paper are in this Twitter threadd visible.
Source: To et al., South China Morning Post, Science Media Center