A study published in the journal The Lancet Infectious Diseases shows the first confirmed case of COVID-19 reinfection in the US – the country worst hit by the pandemic – and shows that exposure to the virus may not be a guarantee of future immunity .
The patient, a 25-year-old Nevada man, was infected with two different variants of SARS-CoV-2, the virus that causes COVID-19, within 48 days.
The second infection was more severe than the first, which resulted in the patient being hospitalized with oxygen assistance.
The paper identified four other globally confirmed cases of reinfection with one patient each in Belgium, the Netherlands, Hong Kong and Ecuador.
Experts said the prospect of re-infection could have a profound impact on how the world battles through the pandemic.
In particular, this could influence the search for a vaccine – the current holy grail of pharmaceutical research.
“The possibility of reinfection could have a significant impact on our understanding of Covid-19 immunity, especially in the absence of an effective vaccine,” said Mark Pandori of the Nevada State Public Health Laboratory and lead author of the study.
“We need more research to understand how long the immunity of people exposed to SARS-CoV-2 lasts and why some of these second infections, while rare, are more serious.”
Vaccines trigger the body’s natural immune response to a specific pathogen and arm it with antibodies to fight off future waves of infection.
However, it is not at all clear how long COVID-19 antibodies last.
In some diseases, such as measles, infection confers lifelong immunity. For other pathogens, immunity can be fleeting at best.
The authors said the US patient could have been exposed to a very high dose of virus the second time, causing a more acute response.
Alternatively, it could be a more virulent strain of the virus.
Another hypothesis is a mechanism known as antibody-dependent enhancement – that is, when antibodies actually make subsequent infections worse, such as with dengue fever.
The researchers pointed out that reinfections of any kind are rare, with only a handful of confirmed cases of tens of millions of COVID-19 infections worldwide.
However, since many cases are asymptomatic and therefore likely not test positive initially, it may be impossible to know whether a particular Covid-19 case is your first or second infection.
In a linked comment to The Lancet, Akiko Iwasaka, professor of immunobiology and molecular, cell and developmental biology at Yale University, said the results could have implications for public health policies.
“As cases of reinfection rise, the scientific community will have an opportunity to better understand the correlates of protection and the incidence of natural immune infections with SARS-CoV-2 that induce this level of immunity,” she said.
“This information is key to understanding which vaccines can cross this threshold to ensure immunity for individuals and herds,” added Iwasaka, who was not involved in the study.
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© Agence France-Presse
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