First US Covid reinfection deepens immunity fears

Reinfection cases have also been confirmed in Belgium, the Netherlands, Hong Kong, and Ecuador

US scientists have confirmed the country’s first case of Covid-19 reinfection, deepening concerns that exposure to the virus may not guarantee total immunity.

A study published by The Lancet showed that a 25-year-old man from Nevada was infected with two distinct variants of Sars-CoV-2 within a 48-day span. The patient’s second infection was more severe, the researchers at the University of Nevada said, resulting in hospitalisation with oxygen support.

At least four other reinfection cases have been confirmed globally – in Belgium, the Netherlands, Hong Kong, and Ecuador – though scientists have suggested the true figure is likely to be much higher.

Professor Mark Pandori, lead author of the US study, warned there are “still many unknowns” about the virus and the immune system’s response. “But our findings signal that a previous Sars-CoV-2 infection may not necessarily protect against future infection,” he added.

The study comes just hours after Donald Trump claimed that he was immune and could no longer catch the virus following his recovery from Covid-19, which has killed more than 210,000 Americans. The Nevada patient was first infected with the virus in April but did not display any serious disease outcomes, the researchers said. In June, he experienced severe Covid-19 symptoms, including fever, cough and nausea, and was later hospitalised before tests confirmed a second positive diagnosis.

Genome sequencing of the patient’s virus samples displayed significant genetic differences, implying he had been infected by two distinct versions of Sars-CoV-2. The US case is the second confirmed example, after the Ecuador study, where reinfection has resulted in a more serious disease outcome.

The patients from Belgium, the Netherlands and Hong Kong did not display worse symptoms after being infected for a second time. “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,” Prof Pandori said.

The authors of the study suggest the Nevada patient may have encountered a very high dose of the virus or a more virulent strain for the second infection, generating a heightened immune reaction. “So far, we’ve only seen a handful of reinfection cases, but that doesn’t mean there aren’t more, especially as many cases of Covid-19 are asymptomatic,” Prof Pandori added.

Paul Hunter, a professor in medicine at the University of East Anglia, said that reinfection was to be expected in some people as a result of waning immunity levels. “Given the fact that to date over 37 million people have had the infection we would have expected to have heard of many more incidents,” he added.

But he warned that the findings were “very concerning both from the point of view of the very short time between the two infections and the fact that the second illness was more severe than the first”.

“Until this and one other recent report from Ecuador I, for one, assumed that any second infection was likely after only a few months and then most likely to be less severe, at least in otherwise immune-competent individuals. Nevertheless, repeat infections do occur with different strains and I suspect many more will be found over coming months as immunity declines in individuals after infection.”

These developments could hold significant implications for the effectiveness of any future vaccines, though experts say there would need to be many more cases of reinfection for these fears to be justified.

“It is too early to say for certain what the implications of these findings are for any immunisation programme,” said Prof Hunter. “But these findings reinforce the point that we still do not know enough about the immune response to this infection.”

Many remain optimistic that a vaccine will be able to provide some form of immunity against the virus, though it remains unclear how long this would last for. Brendan Wren, a professor of microbial pathogenesis at the London School of Hygiene & Tropical Medicine, told The Independent: “The fact that there are so many cases and so few reinfections would suggest there’s an appropriate immune response out there which we can capture with a vaccine. That should give us hope.”

Akiko Iwasaki, a professor of immunobiology and molecular, cellular and developmental biology at Yale University, said the emergence of reinfection cases presented an opportunity for the scientific community to “understand better” how the body’s immune system works in response to the virus. “This information is key to understanding which vaccines are capable of crossing that threshold to confer individual and herd immunity,” she said.