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A 25-year-old Nevada man contracted COVID-19 in April and June, with genomic sequencing confirming differences between the variants, researchers reported in a peer-reviewed journal.

In this case -- which following publication of the -- the man tested positive for SARS-CoV-2 on April 18 and June 5, with two negative tests in May, and the second infection resulted in more severe disease, reported Mark Pandori, PhD, of the University of Nevada Reno School of Medicine, and colleagues, writing in

The first widely reported case of confirmed COVID-19 reinfection occurred in a Hong Kong man in August. However, the Hong Kong patient's infections were in March and August, and he was asymptomatic for the second infection.

"It is important to note this is a singular finding and does not provide generalizability of this phenomenon," Pandori said in a statement. "It also strongly suggests that individuals who have tested positive for SARS-CoV-2 should continue to take serious precautions when it comes to the virus, including social distancing, wearing face masks, and handwashing."

An by Akiko Iwasaki, PhD, of Yale University School of Medicine in New Haven, Connecticut, noted that while only a few cases of reinfection are known, they carry public health implications.

For one thing, Iwasaki wrote, immunity does "not necessarily" protect individuals from disease after being reinfected, because both this Nevada patient and one in Ecuador had worse outcomes after the second infection. Moreover, reinfection is likely underestimated, because the "paucity of broad testing and surveillance" means the system is missing asymptomatic cases.

These cases of reinfection mean "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," Iwasaki wrote, and the safest pathway to herd immunity is through a safe and effective vaccine.

And we should only need one vaccine against SARS-CoV-2, Iwasaki asserted, because different viral isolates do not indicate the second infection was due to "immune evasion."

"There is currently no evidence that a SARS-CoV-2 variant has emerged as a result of immune evasion. For now, one vaccine will be sufficient to confer protection against all circulating variants," she wrote.

Case Details

Pandori and colleagues elaborated on the patient's clinical details. On March 25, the patient started reporting sore throat, cough, headache, nausea and diarrhea, and was tested at a community testing event on April 18. His symptoms resolved by April 27, but on May 31, the patient went to an urgent care clinic with self-reported fever, headache, cough, nausea, and diarrhea. On June 5, the patient's primary care doctor sent him to the emergency department for provision of oxygen, after the patient was found to be hypoxic with shortness of breath.

He required ongoing oxygen support in the hospital, and reported myalgia, cough and shortness of breath. Chest radiography showed "patchy, bilateral, interstitial opacities" indicating atypical pneumonia.

The patient tested positive for SARS-CoV-2 via reverse-transcriptase polymerase chain reaction (RT-PCR) on April 18, followed by two negative tests following the resolution of his symptoms. He then tested positive via RT-PCR on June 5, but IgG and IgM against SARS-CoV-2 were also positive.

Researchers offered several hypotheses for why the second infection might have been worse than the first, such as a high dose of virus might induce more severe disease, that reinfection was caused by a more virulent virus to this patient or it could potentially be due to antibody-mediated enhancement of disease.

They noted the patient had no immunological disorders, was not taking immunosuppressive drugs and was negative for HIV via antibody and RNA testing, with no obvious cell count abnormalities.

The authors said they were unable to undertake any assessment of the immune response to the first infection, and could not fully assess the effectiveness of the immune responses during the second infection.

"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," Pandori said. "Right now, we can only speculate about the cause of reinfection."

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