Growing reports of people experiencing a COVID-19 rebound after taking the antiviral treatment Paxlovid have "refreshed our understanding of the novel coronavirus", a senior Chinese public health expert said on Monday.

The phenomenon suggests that COVID-19 antiviral drugs work by inhibiting the novel coronavirus' replication, rather than killing the virus in an infected patient-employing the same method as medications against HIV, Wu Zunyou, chief epidemiologist at the Chinese Center for Disease Control and Prevention, said on his Sina Weibo social media account.

While stressing that Paxlovid, made by United States' pharmaceutical giant Pfizer, is one of just a handful of effective therapies available at present, Wu said recent rebound cases should serve as a reminder that the development of COVID-19 drugs remains an arduous task.

A COVID-19 rebound is characterized by a recurrence of symptoms or a new positive viral test after having tested negative, according to a health advisory issued by the US Center for Disease Control and Prevention.

A review of clinical trial data submitted by Pfizer showed that 1 to 2 percent of patients had infection rebounds after completing treatment, the US Food and Drug Administration said in May.

One self-reported case in particular attracted the attention of Wu and other health experts around the globe.

David Ho, a renowned virologist at Columbia University who pioneered the discovery of cocktail therapy against HIV/AIDS, said during an interview with Time magazine in May that he tested positive again after taking a five-day course of Paxlovid and having tested negative at least six times.

By using his lab at Columbia University, Ho was able to carefully track his infection and to genome sequence the virus.

"What Ho found is that the second round of positive COVID-19 infection is not because the virus has developed resistance to the drug or mutated. Nor was he infected with another strain of the virus," Wu said. "Instead, it was caused by a 'resurrection' or 'rebound' of the initial infection."

In a case report released on May 23 on Research Square, a preprint platform, Ho looked into 10 rebound cases, including his own. The report was published by researchers from several institutions in the US.

"Two of the 10 cases had transmitted the virus to others when their infections recurred, suggesting their contagiousness was not low," he said, adding that relapsed cases tested negative without further treatment in about three to five days.

Based on its findings, the report suggested patients who have symptomatic relapse following Paxlovid treatment should isolate until antigen testing is negative.

Wu said a COVID-19 rebound after treatment is similar to some cases observed in HIV patients.

Current HIV drugs aim at blocking the virus' replication and suppressing the viral load in a patient below the detectable threshold. But the virus will rebound after suspending treatment and HIV patients need to take medications for life, according to Wu.

"The phenomenon has refreshed our view of the novel coronavirus and made us realize that COVID-19 drugs might not be as convenient as we've imagined and there is a long and strenuous way ahead," he said.

Wu noted that the benefits of COVID-19 antiviral drugs outweigh the risks and Paxlovid can still be used as an effective drug against the disease.