Editor’s note: This story was originally published on May 31, 2022.
People who rebound from Covid-19 after treatment with the antiviral drug Paxlovid may be contagious and may not know it because they may not have symptoms, researchers warn.
“People who rebound are at risk of transmitting to other people, even if they are outside of what people accept as the usual window for being able to transmit,” said Dr. Michael Charness of Veterans Administration Medical Center in Boston. .
Charness and his colleagues recently collaborated with a team of researchers from Columbia University to look at cases of Covid-19 that come back after Paxlovid treatment. He said they have found at least two cases in which people passed on to others when their infection recurs.
In one case, a 67-year-old man infected a 6-month-old child after half an hour near the child.
The man was 12 days after his first positive Covid-19 test. He had taken a five-day course of Paxlovid and was feeling better. He had no symptoms when he saw the baby, who was his grandson, but around eight hours later he started to feel sick again.
The baby tested positive around three days later, as did both parents. Neither the baby nor her parents had any other close contacts before they fell ill.
“This indicates that you can transmit during the rebound even before you develop symptoms,” Charness said. “And you know, we studied a small number of people. It’s certainly conceivable that there are other people who don’t have symptoms and still have a viral rebound.
In another case, a 63-year-old man infected two family members during three days of relapse after Paxlovid.
Based on this research, the US Centers for Disease Control and Prevention released new guidelines last week for people facing Covid-19 rebound after Paxlovid.
The CDC said people who test positive again and whose symptoms return after finishing their antiviral pills should start their isolation period again and self-isolate for five full days. The agency says people can end their self-isolation period after those extra five days as long as their fever has been gone for 24 hours without fever medication and they feel better. The agency also recommends people wear a mask for 10 days after their symptoms return.
The findings and advice come as the use of Paxlovid has increased in the United States. According to the White House, over the past two months, prescriptions filled for Paxlovid have increased from about 27,000 per week to 182,000 per week.
The administration attributes the increase to its Test-to-Treat program, which created one-stop centers at grocery stores and pharmacies where people could take a Covid-19 test and immediately receive and fill a prescription for antiviral drugs. Antiviral drugs should be taken within the first few days of symptoms.
The drug is working well. In clinical trials, Paxlovid reduced the risk that someone at risk for severe Covid-19 would need to be hospitalized by almost 90% compared to a placebo.
For this reason, according to the CDC, early treatment with this drug is always recommended.
As helpful as it is, however, the researchers say people should be aware that the drug may not completely extinguish the infection.
Charness and his co-authors have now collected at least 10 cases of recurrence of Covid-19 after Paxlovid. Half of them come from just two families, which leads the researchers to conclude that such cases are not so rare.
Research is shared as a preprint. It has not been reviewed by outside researchers or published in a medical journal.
Genetic testing suggests that when people get a second round of Covid-19 after Paxlovid, it’s not because they were infected with a different strain of the virus. There is also no sign that the virus has changed or mutated to develop any sort of resistance to the drug.
Rebound cases have been mild so far. There have been no reports of serious illness during a relapse of Covid-19. For this reason, according to the CDC, there is no reason to believe that more treatment is needed.
Why this might happen is still a mystery.
In his studies, Charness said, researchers observed the amount of virus in a person’s body — called their viral load — decrease with Paxlovid treatment.
“People take Paxlovid, and what we know it does really well is block viral replication,” he said. And so the virus levels go down. But then, in some people — no one knows how many, because too few people have been studied — virus levels start to climb again nine to 12 days after they first test positive, Charness said.
It is not entirely clear that this rebound is related to Paxlovid. In studies of more than 2,200 patients with Covid-19, Pfizer, the company that makes the drug, said a few patients saw their Covid-19 rebound after testing negative, but they were among the group that took Paxlovid as well as in those who received the placebo, suggesting that Covid reappears in some people, even without treatment.
The Charness team, however, did their own comparative study and found something different. When researchers looked at 1,000 cases of Covid-19 diagnosed between December and March among National Basketball Association players and support staff who had not taken the drug, they found no returning cases of Covid. -19. This study is still unpublished.
They say more research is needed to understand if there might be a link to the drug.
Charness said the fact that the infection can come back this way after treatment raises some questions. For one, would rebound also be common in people who started the drug later, perhaps on the fourth or fifth day after their first symptoms, after their immune system had had more time to initially see the virus ? Would longer treatment — perhaps taking the drug for six or seven days, rather than five — reduce the risk of the virus coming back?
“Nobody knows,” he said. “Someone should study this.”