Covid reinfection: Experts caution over handful of isolated global cases

A man in the US tested positive for the virus in April and June, prompting fresh debate over how common reinfection is

An employee wears a Continental-branded protective face mask at the Continental AG factory in Hanover, Germany. Bloomberg

An Indian woman mourns after taking a glimpse of her husband's body, a victim of Covid-19, at a cremation ground in Gauhati, India. AP Photo

Workers place signs with portraits of health workers who died from Covid-19 at the Venezuelan Medical Federation in Caracas, Venezuela. AFP

A Covid-19 test that came out positive is seen on a chair during a doctor's visit in Ate, on the eastern outskirts of Lima, in Peru. AFP

Men wait in a distanced line to get tested for Covid-19 aboard a trajinera, one of the colorful wooden boats popular with tourists and revelers, in the Xochimilco district of Mexico City. AP Photo

A nurse prepares to inoculate volunteer Ilya Dubrovin, 36, with Russia's new coronavirus vaccine in a post-registration trials at a clinic in Moscow. AFP

Netherland's King Willem-Alexander looks on as he visits a coronavirus (Covid-19) test site in Leiderdorp, The Netherlands. AFP

Workers check disinfection tunnels at the Capital University of Science and Technology in Islamabad, Pakistan. AFP

A worker disinfects a bus stop in Banda Aceh, Indonesia. AFP

A boy shares his breakfast with the birds of the central park after begging with his father, in Tegucigalpa, Honduras. EPA

Migrants from different nationalities rest on board the Spanish NGO Open Arms vessel after being rescued in international waters, in the Central Mediterranean sea. AP Photo

A child sits down during his first on-site day at Albino Nunez school after months of lockdown in Ourense, Spain. EPA

New Zealand Prime Minister Jacinda Ardern visits inMusic in Auckland, New Zealand. Getty Images

Johnny Lopez makes his way past a mural on the side of Hideaway Pizza on Rockford Ave. while walking home from work in Tulsa, Oklahoma, USA. Tulsa World via AP

The news that a man in Nevada in the US has been infected with the coronavirus twice has made headlines around the world – but scientists say its significance is unclear.

While indicating that reinfection is possible, researchers stress it is only a single case and may not offer useful information as to whether reinfection is common.

Researchers reported in the journal The Lancet this week that the 25-year-old man, who tested positive in April and June, suffered more severe symptoms on reinfection and had to be hospitalised.

It was not the first confirmed reinfection, with at least three other people – a 33-year-old man in Hong Kong, a 51-year-old woman in Belgium and a 46-year-old man in Ecuador – having previously been reported to have had Covid-19 twice.

The case in Nevada has sparked particular concern because the second infection was more severe than the first.

This could suggest the immune system, in producing antibodies against the first infection, ended up assisting rather than preventing the subsequent infection.

However, out of the other three confirmed reinfections, the second infection was less severe than the first in one case, while in another it was asymptomatic.

Data suggest reinfection is rare

Paul Hunter, a professor in medicine at the University of East Anglia in the UK, told the Science Media Centre that there may have been many reinfections where the second illness was less severe or asymptomatic, but these have simply been missed.

“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 if such very early reinfections with severe illness were common,” he said.

“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.”

John Oxford, professor emeritus at the University of London and co-author of the textbook Human Virology, cautioned against reading too much from the findings.

“Every virus I’ve seen, as far as I know, you’re never totally immune. When you get infected, you can never be 100 per cent [sure] you won’t be reinfected,” he said.

The question of whether people who have recovered from a coronavirus infection can be reinfected has been a main talking point during the pandemic.

Typically, the body produces antibodies against the coronavirus about a week after symptoms appear, although the degree to which they offer protection against reinfection has been unclear, according to the British Society for Immunology.

Second Covid-19 infection raises questions over herd immunity

As many as one in five people who have been infected produce few or no detectable antibodies in their blood.

The body’s immune response does not just involve antibodies, with white blood cells called T cells also playing an important role.

If people cannot be reinfected, it offers hope that as the numbers who have had Covid-19 increase, transmission rates will decline because more people are immune, eventually reaching what is called herd immunity.

The case in Nevada, confirmed as two separate infections because genetic differences were found between the viruses during the two positive cases, has been interpreted by some commentators as suggesting herd immunity may be less likely to develop.

As well as potentially having implications for herd immunity, if reinfections turned out to be common it could also cast doubt on the effectiveness of immunisation programmes, as it may indicate that a vaccinated person could still be at risk of infection.

Vaccines are not, though, expected to confer immunity on all who receive them, so isolated cases of reinfection may offer little insight into the likely effectiveness of such programmes.

Prof Oxford said that he was optimistic about the vaccines under development, some of which are expected to receive clearance for widespread use in the coming months.

“Despite these reinfections, I think some of them are going to work, I really do,” he said. “Which one is another question.”