The patient walked into the Washoe County community testing station in the US state of Nevada on April 18 with a sore throat, dry cough and a headache, but no reason to worry.
He was only 25, had no prior medical conditions, and although the PCR nasal-swab test for Covid-19 he took came back positive, he was soon feeling well again.
Thirty five days later, he was rushed to the emergency room, short of breath and with a raging fever, and placed on oxygen support.
He had become the first confirmed US case of Covid-19 reinfection.
Up to now, there have been only a handful of similar cases worldwide, and experts say it is too early to draw sweeping conclusions from such a small head count.
But the prospect of getting reinfected with Covid-19 — and getting even sicker the second time around — could have a significant impact on how governments chart the path out of the pandemic.
In particular, reinfections may render the idea of herd immunity — that is, a sufficiently high percentage of people eventually becoming immune to Covid-19 — unrealistic.
“Reinfection cases mean that in some people, the immune response is not enough to protect them from infection or disease,” Akiko Iwasaka, a professor of Immunobiology and Molecular, Cellular and Developmental Biology at Yale University, told AFP.
“Reinfections from SARS-CoV-2 (the virus that causes Covid-19) mean that immunity acquired through natural infection is not perfect.”
Researchers who documented the Nevada patient’s case offered a number of possible explanations as to how he could have gotten sick twice.
He may have been exposed to a very high dose of the virus the second time around, triggering a more acute reaction.
Alternatively, it may have been a more virulent strain of the virus.
The study, published this week in The Lancet Infectious Diseases, listed other confirmed reinfections in Belgium, the Netherlands, Hong Kong and Ecuador.
– Too soon to tell? –
Frederic Altare, director of Immunology at the Inserm Research Centre of Oncology and Immunology Nantes-Angers, said there was currently little evidence that Covid-19 reinfection was going to be a “major issue” given the low case figures.
“With the number of people who have been infected there are only a dozen or so proven reinfections — that’s not much,” he told AFP.
But others said it was difficult to accurately gauge reinfection numbers given the relative lack of testing during the first wave this spring.
In other words, many people could have in theory been infected in March or April and remained asymptomatic, only to test positive later in the year when they were reinfected, but this time with symptoms.
According to Jeffrey Shaman, professor of Environmental Health Sciences at the Columbia University Mailman School of Public Health, the main obstacle to ascertaining reinfection numbers is that SARS-CoV-2 — unlike other coronaviruses that circulate among humans — is brand new, epidemiologically speaking.
“The world has only been dealing with this for a number of months,”