First Confirmed Case of Coronavirus Reinfection Doesn’t Mean We’re All Doomed

The case is one in 23 million

Photo: Li Zhihua/China News Service/Getty Images

Scientists in Hong Kong reported today the first confirmed case of reinfection with SARS-CoV-2, the virus that causes Covid-19. Since the beginning of the pandemic, there have been concerns about long-term immunity to the novel coronavirus, and several possible cases of reinfection were reported in the media. But until now, none were confirmed scientifically.

The question has always been whether reports of a person testing positive, recovering from the virus and testing negative, and then testing positive again weeks or months later is because of faulty testing, “dead” viral RNA lingering in the body, a reemergence of the same infection, or a genuine instance of reinfection. The Hong Kong report is the first to use genetic testing to confirm the two cases in the same person were caused by slightly different strains of the virus.

According to a manuscript leaked by South China Morning Post reporter Lilian Cheng on Twitter, the patient, a 33-year-old man with no preexisting conditions, first got sick in March, presenting with a cough, sore throat, fever, and headache. He tested positive for SARS-CoV-2 on March 26 and was monitored in the hospital for two weeks (standard protocol for patients in Hong Kong regardless of disease severity) until he was discharged on April 14 following two negative tests. The second time he tested positive was after returning to Hong Kong from Spain on August 15, when he was screened at the airport as part of standard reentry procedures. This time, however, he was completely asymptomatic and never developed a cough, fever, or any other signs of Covid-19.

Scientists at the University of Hong Kong sequenced the genome of the virus from the tests taken in March and August and discovered that they differed in several key areas, indicating that they were two different strains of SARS-CoV-2. Specifically, 24 nucleotides — the “building blocks” that make up the virus’s RNA — were different between the two infections. The August strain was a variation of the virus known to be circulating primarily in western Europe, suggesting the man was reinfected while abroad.

While the news of a legitimate reinfection is worrying, virologists and immunologists took to Twitter to reassure people that this doesn’t mean we’re all doomed. In fact, scientists have been expecting reinfection to occur all along. Akiko Iwasaki, PhD, a professor of immunobiology at Yale University, tweeted, “This is no cause for alarm — this is a textbook example of how immunity should work.”

Virus-specific antibodies created by the immune system are central to the question of immunity, and varying reports have emerged over the past few months about the quantity, quality, and duration of antibodies produced in response to SARS-CoV-2. The vast majority of people who’ve recovered from Covid-19 do develop antibodies to the virus, and typically the more severe the infection, the more antibodies they produce, providing them with protection against reinfection. However, according to the leaked manuscript, which is under review at the academic journal Clinical Infectious Diseases, the Hong Kong patient had no detectable antibodies after his first infection.

It’s possible this man had a very mild initial case of Covid-19 or an abnormal immune response that resulted in fewer antibodies being produced. Either way, the absence of antibodies after the man’s first infection could explain how he became infected with a different strain a second time. In contrast, a preprint study published earlier this month and covered in the New York Times reported that three people who tested positive for antibodies were spared in a large outbreak that infected 104 people on a fishing boat from Seattle.

Given that most people do develop antibodies to the virus, Angela Rasmussen, PhD, a virologist at Columbia University, tweeted that the Hong Kong case “doesn’t have major implications for immunity since most people DO have IgG [antibodies] after recovering from infection.”

The fact that the second case was asymptomatic is also a good sign because it suggests that there is some protection (perhaps from T cells) that made the second infection less severe. “While immunity was not enough to block reinfection, it protected the person from disease,” Iwasaki tweeted. What’s more, the man developed a robust antibody response after the second infection.

Finally, it’s important to remember that this is one confirmed case of reinfection out of the more than 23 million cases of Covid-19 worldwide, and one in 23 million is pretty good odds. As Rasmussen pointed out on Twitter, “How many people were screened to find this single case of reinfection? There’s no indication that this is anything other than a rare case of someone getting reinfected after not developing immunity to the first infection.”

Health and science writer • PhD in 🧠 • Words in Scientific American, STAT, The Atlantic, The Guardian • Award-winning Covid-19 coverage for Elemental

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