Last week, Wisconsin news reported that a local woman had tested positive for Covid-19 a second time. The patient’s initial infection was more than three months earlier.
However, no further details were forthcoming from the local health authorities. It is not clear if the woman was re-infected or was, instead, one of the many suffering long-term Covid-19.
Can you be reinfected with coronavirus?
It might seem like a niche concern, with most of the country focused on not catching the virus in the first place. But the answer has surprisingly far-reaching consequences.
Most importantly, if people can be re-infected with SARS-CoV-2, there is no prospect of the population reaching a natural stage of herd immunity. It also relates to the effectiveness of any potential vaccine against the virus.
Put differently, for a person to catch the coronavirus for a second time, their immune response to the virus has to have degraded to such a point that they again become vulnerable to infection. If the human immune response to SARS-CoV-2 is not long-lasting, the response to a vaccine may not be either.
Investigations of the subject thus far have not been encouraging. A Kings College London study found that although 60% of those exposed to Covid-19 developed a potent immune response, only 17% maintained the same anti-Covid-19 antibody levels two months later.
Virology Professor Nigel McMillan explains that this is a common feature of coronaviruses, which include the common cold. Antibodies to the cold tend to be gone six to 12 months after infection.
“Coronaviruses in general seems to be particularly good at not being well recognised by our immune system,” says Professor McMillan. “A feature of common cold coronaviruses is that people get reinfected by them all the time.”
While this is somewhat depressing news, it’s important to also recognise that vaccines can work in ways the human immune system does not.
With this in mind, the project manager of the Oxford University vaccine development team, Dr Rebecca Ashfield, said that with any prospective vaccine, “We’re likely to need yearly boosters, similar to annual flu jabs.”