A 33-year-old man in Hong Kong may represent the first confirmed case of reinfection, researchers in Hong Kong said. He was reinfected with the novel coronavirus, but didn't develop any symptoms the second time. Viral sequence disparity indicates Hong Kong case not simply prolonged infection.

The man was diagnosed with COVID-19 on March 26, hospitalized, then recovered. He tested positive for SARS-CoV-2 again on August 15, and whole genome sequencing of viral isolates from the two episodes indicated they were from different clades, reported Kwok-Yung Yuen, MD, of the University of Hong Kong, and colleagues in a manuscript they said had been accepted for publication in Clinical Infectious Diseases, but not yet published.

"We report the first case of reinfection of COVID-19," they wrote. "Epidemiological, clinical, serological and genomic analyses confirmed that the patient had reinfection instead of persistent viral shedding from first infection."

Evidence:

Indeed, whole genome sequencing found the first viral genome was most closely related to SARS-CoV-2 strains from the U.S. or England collected in March/April strain and the second viral genome was most closely related to strains from Switzerland and England in July/August. There were 24 nucleotide differences suggesting different strains.

Other evidence the authors offered that the patient had an acute infection in August was his elevated C-reactive protein level and "relatively high viral load with gradual decline." They also pointed to the long period -- 142 days -- between infections, saying prior research found viral RNA is undetectable one month after symptom onset, and prolonged viral shedding has only ever been documented up to 104 days after infection.

Clinical Manifestation:

Yuen and colleagues reported that the man experienced fever and a deep, productive cough during the March episode, at which point he tested positive for SARS-CoV-2. He was discharged on April 14 after two negative SARS-CoV-2 tests, taken a day apart.

But in August, the man was returning to Hong Kong from Spain via the United Kingdom, and tested positive for SARS-CoV-2 upon reentry screening at the Hong Kong airport. He was hospitalized, but remained asymptomatic and afebrile.

Investigation Findings

The only lab abnormalities were hypokalemia and the slightly elevated CRP, which declined during hospitalization. The patient's SARS-CoV-2 load fell during hospitalization, based on serial PCR testing.

Ten days after the first onset and a day after the second onset, the patient tested negative for IgG against SARS-CoV-2. Only serum specimens collected on day 5 after the second hospitalization tested positive for IgG.

Clinical Findings & Observations

"Our findings suggest that SARS-CoV-2 may persist in the global human population as is the case for other common-cold associated human coronaviruses, even if patients have acquired immunity via natural infection," said a press release emailed from HKU Med.

When asked about implications for COVID-19 vaccine development, Spinelli noted that no vaccine to a respiratory virus like this is expected to be 100% effective -- much like the flu shot, which reduces infection incidence and illness severity but only to a degree.

"The fact that the second infection had much reduced severity is what we'd expect to see with a vaccine. Hopefully, a vaccine will induce more rigorous immunity," he said.

This case of re-infection has "several important implications," the authors wrote in the study. "It is unlikely that herd immunity can eliminate SARS-CoV-2, although it is possible that subsequent infections may be milder than the first infection as for this patient." 

COVID-19 will likely continue to circulate in the human population, similar to the coronaviruses that cause common colds, they wrote.