A 33-year-old man is confirmed as the first case of coronavirus reinfection after he traveled from Hong Kong to Spain — but experts say it's no cause for panic

• Scientists have confirmed the first case of someone getting the coronavirus twice: A 33-year-old, healthy man from Hong Kong was reinfected four months after his first infection ended.
• While he was hospitalized with a headache, fever, and cough the first time he fell ill, the patient had no coronavirus symptoms when he was recently re-diagnosed, in August.
• This finding isn't cause for concern: It shows that our immune system mounts an adequate defense against this virus — a defense that can help fend off the illness' worst effects a second time around.
• Vaccines could build up our communal coronavirus immunity faster and help stamp out the virus's global spread as early as next year.

A healthy, 33-year-old man has provided researchers in Hong Kong with some of the first definitive evidence that people can get the novel coronavirus twice.

"This is the world's first documentation of a patient who recovered from COVID-19 but got another episode of COVID-19, afterwards," researchers from Hong Kong University said in a press release on Monday, as they announced their reinfection study has been accepted for publication in the peer-reviewed medical journal Clinical Infectious Diseases.

This case isn't reason for the general public to panic, though. Instead, it shows how previous infections can provide people with some decent protection from another coronavirus illness. Because while the man in this study had some of the most worrisome symptoms of COVID-19 when he first got sick back in March, he had no coronavirus symptoms on his second time around. Many epidemiologists have anticipated coronavirus reinfections just like his could be possible.

"You can get it again," Florian Krammer, a vaccine scientist and virus expert at the Icahn School of Medicine at Mount Sinai in New York, previously told Business Insider, when asked about coronavirus immunity.

Indeed, experts like Krammer have predicted (just as this case from Hong Kong suggests) that a patient's second tangle with COVID-19, the disease caused by the novel coronavirus, will be less severe than their first: "It's very likely that if you did get reinfected after some time, it would be an attenuated disease," he said.

This case is some of the first reassuring data we have that supports the idea that the response our bodies mount to coronavirus infections — though imperfect at preventing future illnesses — will likely help us better fight off subsequent viral threats. So, too, could many of the coronavirus vaccines that are in development now, even if they don't protect everyone from infection 100%.

"I don't want people to be afraid," Maria van Kerkhove, the World Health Organization's technical lead for COVID-19, said on Monday when asked about the new study. "We need to ensure that people understand that when they are infected, even when they have a mild infection, that they do develop an immune response."

His reinfection involved a trip to Spain

A cough, sore throat, headache, and fever. Those were the tell-tale symptoms this man displayed in the spring, before he tested positive for the coronavirus on March 26 in Hong Kong, and was hospitalized for over two weeks. He was discharged on April 14, when his coronavirus tests came back negative.

Four months later, the man was feeling perfectly fine while traveling home from a trip to Spain. On August 15, he tested positive for the virus, a second time, during a throat swab screening at Hong Kong's airport. At the time he had no fever, a normal pulse rate, and an "unremarkable" physical exam, the study authors said.

By traveling to Europe during the pandemic, the man appears to have caught a "completely different" circulating strain of the virus than he did the first time around, the study authors said. The researchers performed a whole genome analysis on both of his infections to determine they were caused by different iterations of the virus.

The patient's high viral load during his second infection, and the lapse of several months between his first and second diagnosis, point to the conclusion that these were indeed two separate infections, rather than the same lingering case of COVID-19.

It's not abnormal to get coronaviruses over and over again

The new report backs up what epidemiologists have been stressing for months: coronavirus immunity is not iron-clad. With some diseases, like measles or hepatitis A, infection is a one-and-done deal. Once you get sick and recover, you're immune for life.

"For human coronaviruses, that's not the case," Krammer said, adding, "You can get repeatedly infected once your immunity goes down."

People can catch coronaviruses that cause common colds multiple times, but the "second time is usually milder, or even asymptomatic," he added.

In fact, somewhat like an inoculation, the colds you got years ago may prove helpful if your body has to fight the novel coronavirus.

According to a study published earlier this month, some people who've never been exposed to the novel coronavirus may nonetheless have T cells — white blood cells that track down and kill invading pathogens — that recognize this virus. Scientists think that's because those cells previously learned how to identify and fight coronaviruses that cause common colds, and now have an immunological leg-up against the novel coronavirus.

Possible re-infections have occurred in a few cases, out of millions

Over the past nine months, more than 23.5 million novel coronavirus cases have been reported worldwide. Of those 23.5 million cases, only a handful, at most, have been confirmed reinfections.

In June, researchers reported a possible case of coronavirus reinfection: an 82-year-old man in the US with preexisting health conditions tested positive for the virus 55 days after his initial diagnosis.

Another study, published in July, described two 84-year-olds and one 90-year-old in France who tested positive for coronavirus in late March and early April, and then again in early May after being symptom free for weeks. All three patients died later that month.

Unlike the Hong Kong case, however, these cases were not classed as confirmed reinfections: scientists did not sequence the genomes of their viral infections, and the timespan between infection and suspected reinfection was shorter.

Some suspected reinfection cases have turned out to be false. More than 260 people in South Korea who recovered and tested negative for the virus subsequently tested positive again in April. After further study, the Korea Center for Disease Control and Prevention concluded that these individuals' hadn't gotten sick again, but rather subsequent coronavirus tests had picked up dead virus fragments that were lingering in patients' bodies after they recovered.

These recovered patients were not infectious when they tested positive again.

Getting vaccinated will help us stamp out the pandemic

The cases of reinfections suggest that our immunity to the virus — whether generated in response to an infection or as the result of a vaccine — is likely transient.

But a coronavirus vaccine will still be critical to help stamp out the pandemic, even if its protective benefits aren't indefinite, Krammer said.

"This happens for a lot of vaccines," he previously told Business Insider. "It's not a problem. You can get revaccinated."

That's what booster shots are for. Your tetanus shot, for example, requires a booster every decade. The question now is whether follow-up coronavirus vaccine shots will be needed on a scale of months, and not years.

But "the likelihood of everyone's immunity running out at the same time would be very slim," Walt Orenstein, a vaccinologist and the former director of the US National Immunization Program, told Business Insider.

The whole point of a vaccine is to help a population achieve herd immunity: when enough people are immune to the virus at the same time that it no longer spreads within a community. In this way, vaccines given out en masse can protect everyone, even people who aren't immune.

"Any type of herd immunity is better than zero," Orenstein said. "Increasing the number of immune people in the population, even for a little while, is still going to result in breaks in the transmission chain and reduce the chances more people will get ill."

Bill Gates agreed that "because of cross-protection from other vaccines and coronaviruses" the addition of a coronavirus vaccine, even among 30% to 40% of a population, "may stop exponential spread" of the pandemic by next year.

"You can imagine that by late 2021, you would have enough doses [of a vaccine circulated] that you're almost done," he said in a recent interview with The Economist, predicting the end of the pandemic.