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Infectious Diseases

Updated 15 October 2020

Case study on Covid reinfection: While rare, it's possible that symptoms may be more severe second time around

New research shows the possibility of experiencing more severe Covid-19 symptoms upon reinfection.

  • In a new case study, a Nevada patient is reported to have contracted SARS-CoV-2 twice
  • The second infection was more severe and he required oxygen support
  • The authors of the study offer some possible explanations as to why this may happen

As scientists are trying to make sense of SARS-CoV-2, the virus that causes Covid-19, a new study has found that not only is reinfection possible, but that individuals may actually experience more severe symptoms the second time they are infected.

The study, published in The Lancet Infectious Diseases, reports on the first confirmed case of SARS-CoV-2 reinfection in the US, and cautions that exposure to the virus and subsequent antibodies may not guarantee immunity against a second reinfection.

“Our findings have implications for the role of vaccination in response to Covid-19,” the study authors write.

“If we have truly reported a case of reinfection, initial exposure to SARS-CoV-2 might not result in a level of immunity that is 100% protective for all individuals.”

Case study: patient required oxygen support 

According to the report, the patient, a 25-year-old Nevada man, was infected with two distinct variants of the virus within a 48-day time frame.

The patient’s second and more severe infection resulted in hospitalisation with oxygen support.

The authors also confirmed that the patient had no immunological disorders, nor was he taking any immunosuppressive drugs. He also tested negative for HIV by antibody and RNA testing, and had no obvious cell count abnormalities.

They also mentioned four other confirmed cases of reinfection globally:

“Similar to observations with the reinfection case in Ecuador, our patient showed increased symptom severity in their second infection, whereas the cases from Belgium and the Netherlands and Hong Kong did not show a difference in severity of symptoms,” they explained.

According to Agence France-Presse, Mark Pandori, from the Nevada State Public Health Laboratory and senior study author, explained that the possibility of reinfections could have significant implications in the context of Covid-19 immunity, especially considering no effective vaccine has yet been approved.

"We need more research to understand how long immunity may last for people exposed to SARS-CoV-2 and why some of these second infections, while rare, are presenting as more severe," Pandori said.

Possible explanations

While it is not exactly clear why the second infection in the Nevada patient’s case was more severe than the first, the authors explained that the patient could have been exposed to a very high dose of the virus the second time around, which ended up triggering a more acute reaction.

Alternatively, they proposed that it may have been a more virulent (more harmful) strain of the virus that led to severe infection. A previous Health24 article explains that due to the virus’s complex biology, it is constantly mutating. Scientists are therefore trying to stay ahead, as the most worrying mutations could cause the virus to evade immune systems, as well as vaccines and antibody therapies.

Earlier this month, Health24 also reported on the "silent" reinfection of two Indian healthcare workers who were infected with a completely different strain of the virus the second time around.

A third possible explanation, they wrote, might be due to a mechanism known as antibody-dependent enhancement (ADE) which occurs when antibodies worsen subsequent infections. This has been seen in the case of dengue fever.

Researchers of a separate study published in Nature, said that ADE is a concern for the development of vaccines and antibody therapies as there is the potential of amplifying an infection or triggering harmful immunopathology.

“This possibility requires careful consideration at this critical point in the pandemic of coronavirus disease 2019 (Covid-19),” they wrote.

No need for panic as reinfection remains rare

Despite the concerning findings, the researchers stressed that reinfection remains rare, considering only a handful of cases out of millions have been confirmed globally.

On the other hand, one has to bear in mind that many cases are asymptomatic (displaying no symptoms) and therefore may not test positive for SARS-CoV-2 initially, making it impossible to know if a confirmed case is the first or second infection.

In a linked comment to the study, Akiko Iwasaka, a professor of Immunobiology and Molecular, Cellular and Developmental Biology at Yale University, said the findings could impact public health measures.

"As more cases of reinfection surface, the scientific community will have the opportunity to understand better the correlates of protection and how frequently natural infections with SARS-CoV-2 induce that level of immunity," Iwasaka said. The professor was not involved in the study.

"This information is key to understanding which vaccines are capable of crossing that threshold to confer individual and herd immunity," she added.