In several instances, doctors reported possible reinfections during the pandemic. Mostly, however, they could not rule out that the second infection was not due to faulty testing procedures, false-negative test results or virus residues from the first infection.
But now, new infections have occurred in Hong Kong, the Netherlands and Belgium. In these cases, the patients who had already recovered from previous COVID-19 infections have been reinfected months later with an apparently mutated variant of SARS-CoV-2.
Different cases, similar courses
A 33-year-old man from Hong Kong had mild COVID-19 symptoms in mid-March and tested positive for SARS CoV-2 on March 26. He remained in hospital until he was released on April 14 after two negative PCR tests.
Health authorities believe the man was infected a second time while on a business trip to Spain. A test conducted at Hong Kong airport on August 15 turned out positive. As a precaution, the man was taken to hospital again, although he showed no symptoms.
Genetic analyses showed he had contracted a mutated variant of the virus.
"The analyses showed that the first viral genome belonged to a different strain of SARS-CoV-2 than the second," said Dr. Kelvin Kai-Wang To, a clinical associate professor from the Department of Microbiology at the University of Hong Kong (HKU). According to the study, both virus variants differed in 24 nucleotides, the building blocks of the genetic material.
Scientists are aware that SARS-CoV-2 has mutated several times during the pandemic, repeatedly changing parts of its protein structure, as is common with viruses.
For the researchers, this case is clearly a new infection. Even after surviving COVID-19, it is still possible to become infected with a SARS-CoV-2 pathogen. Such reinfections also occur more frequently with other seasonal cold viruses such as coronaviruses 229E, OC43, NL63 and HKUI24, according to the Hong Kong researchers.
Two cases in Europe
According to Marion Koopmans, a virologist and adviser to the Dutch government, the genetic code of the second infection is also significantly different from that of the first, in the case of the patient in the Netherlands. It was an older man with a weak immune system. This speaks against a resurgence of the first infection, she added.
Koopmans said it was not surprising that new infections were turning up among people who recovered from COVID-19.
"We know from other respiratory tract infections that one is not protected for life, and we do not expect this from COVID-19," the virologist said on Dutch radio.
However, it must now be clarified whether such repeat infections actually occur more frequently or whether they are isolated cases.
In Belgium, one patient took ill again after three months. A gene sequence analysis also revealed that the virus had 11 mutations in the second case. "This is not good news," said virologist Marc Van Ranst on the Belgian channel VTM.
Many open questions
The apparent reinfections add to indications that immunity to SARS-CoV-2 is short-lived. Even after surviving the COVID-19 disease, at least some patients have only partial protection. Not all of them seem to develop protective antibodies.
However, even eight months after the outbreak of the pandemic, many questions remain unanswered, and it is difficult for researchers to gain an overview of the details of global infections as research is conducted worldwide, with many results published quickly and without the necessary peer review.
Detailed studies on the cases in the Netherlands and Belgium are not yet available. There are also only excerpts from a specialist article on the documented repeat infection in Hong Kong that a reporter from the South China Morning Post posted on Twitter. These results have not yet been subject to peer review.
What does this mean for a vaccine?
More than 150 vaccines against SARS-CoV-2 are currently being developed worldwide. Recently, Russia has approved the vaccine "Sputnik V," and seven other vaccine candidates are in the decisive clinical Phase III tests.
If reinfections are indeed confirmed, SARS-CoV-2 is unlikely to disappear due to effective herd immunity. It is also possible that vaccines currently in development may not provide lifelong protection against the aggressive coronavirus.
Until Phase III clinical trials are completed and meaningful long-term studies are available, it is not possible to make reliable statements about how effective these vaccines are, whether they will protect against viral mutations or how long the protection will last.