Researchers have documented the first case of Covid-19 reinfection in the U.S., casting further doubts on the idea of a natural herd immunity and raising the prospect of more serious second infections.
A 25-year old man was treated in hospital after he caught Covid-19 for a second time, doctors report in The Lancet, with the second infection being far more serious than the first.
His treatment came after his lungs could not get enough oxygen into his body, and he has since recovered.
Genetic studies show the man to have contracted Covid-19 on two separate occasions.
The researchers say this raises questions over how long immunity to Covid-19 might last, which has implications on vaccine development and restrictions put in place to safeguard public health.
The researchers say people should follow “identical precautions to avoid infection” whether or not they have previously had the virus.
Though reinfections with Covid-19 are exceptionally rare — there are cases reported in Hong Kong, Belgium, the Netherlands, and Ecuador — they can teach us a lot about the nature of immunity and inform public health efforts to curb the virus’ spread. Crucially, cases of reinfection give reason to question strategies relying on natural herd immunity, researchers say, and ought encourage those who have already been infected to think twice before abandoning precautions and going back to life as ‘normal’.
What To Watch For
The information gathered from reinfection cases could be especially important as the pandemic progresses, and we will potentially start to see more cases as immunity possibly wanes for those infected early on, according to researchers. Particularly troubling in this reported case is the more serious second infection in this example, which runs counter to the prevailing assumption that any second infection would be less severe.
Yale professor of immunobiology Akiko Iwasaki told the Financial Times that as more cases of reinfection arise, there will be better opportunities to understand the relationship between protection and natural infections of Sars-Cov-2. “This information is key to understanding which vaccines are capable of crossing that threshold to confer individual and herd immunity,” she said. Iwasaki added: “Reinfection cases tell us that we cannot rely on immunity acquired by natural infection to confer herd immunity. Not only is this strategy lethal for many but also it is not effective. Herd immunity requires safe and effective vaccines.”