“People who experience a bounce run the risk of transmitting to other people, even though they are out of what people accept as a normal window to be able to transmit,” said Dr. Michael Charness of the Veterans Administration Medical Center. of Boston.
Charness and colleagues recently collaborated with a team of researchers at Columbia University to investigate cases of Covid-19 returning after treatment with Paxlovid. He said they have found at least two cases in which people have been transmitted to others when their infection is repeated.
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 test for Covid-19. He had taken a five-day Paxlovid course and was feeling better. She had no symptoms when she saw the baby, who was her grandson, but about eight hours later she felt sick again.
The baby tested positive about three days later, as did his parents. Neither the baby nor his parents had any other close contact before he became ill.
“It indicates that it can be transmitted during the bounce even before it develops symptoms,” Charness said. “And we know, we studied a small number of people. It’s certainly conceivable that there are other people who have no symptoms and still have a viral rebound.”
In another case, a 63-year-old man infected two family members during a three-day relapse after Paxlovid.
Take precautions after Paxlovid
Based on this research, the U.S. Centers for Disease Control and Prevention issued a new guide last week for people suffering from a Covid-19 rebound after Paxlovid.
The CDC said people who test positive again and symptoms return after they run out of antiviral pills should restart their isolation period and isolate themselves for a full five days. The agency says people can end their isolation period after those extra five days, as long as the fever goes away for 24 hours without medication to reduce the fever and make them feel better. The agency also recommends that people wear a mask for 10 days after their symptoms return.
Findings and guidelines come as Paxlovid use has increased in the United States. According to the White House, over the past two months, Paxlovid’s filled recipes have increased from about 27,000 a week to 182,000 a week.
The administration attributes the increase to its trial testing program, which created unique centers in grocery and drugstore stores where people could get a Covid-19 test and immediately receive and fill a prescription for antiviral drugs. Antiviral drugs should be taken during the first days of symptoms.
The drug works well. In clinical trials, Paxlovid reduced the chances of a person at risk for severe Covid-19 being hospitalized by almost 90% compared to placebo.
For this reason, the CDC says, early treatment with this drug is still recommended.
However useful it may be, however, researchers say people should be aware that the drug cannot completely extinguish the infection.
Charness and 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 researchers to conclude that such cases are not so rare.
The research is shared as a prepress. It has not been examined by outside researchers or published in a medical journal.
Genetic testing suggests that when people have a second round of Covid-19 after Paxlovid, it is not because they have been infected by a different strain of the virus. There is also no indication that the virus has changed or mutated to develop any resistance to the drug.
So far, the rebound has been mild. There were no reports of serious illness during a Covid-19 relapse. That’s why, the CDC says, there’s no reason to think more treatment is needed.
The cause is not yet known
Why this might happen is still a mystery.
In their studies, Charness said, researchers found that the amount of virus in a person’s body, called a viral load, went down with Paxlovid treatment.
“People take Paxlovid, and what we know it does very well is that it blocks viral replication,” he said. And so the virus levels go down. But then in some people, no one knows how many, because not enough people have been studied, the virus levels start to rise again again to 12 days after the first positive test, Charness said.
It is not entirely clear whether this bounce is linked to Paxlovid. In studies of more than 2,200 patients with Covid-19, Pfizer, the company that makes the drug, said there were a few patients who regained their Covid-19 after a negative test, but were in the group. who took Paxlovid as well as those who received placebo, suggesting that Covid only reappears in some people, even without treatment.
The Charness team did their own comparative study, though, and found something different. When investigators analyzed 1,000 cases of Covid-19 diagnosed between December and March in players and support staff of the National Basketball Association who had not taken the drug, they found no case of Covid-19 returning. This study is still unpublished.
They say more research is needed to understand if there could be any connection to the drug.
Charness said the fact that the infection may return this way after treatment raises some questions. On the one hand, would the rebound be so common in people who started the drug later, perhaps on day four or five after the first symptoms, after their immune system has had more time to see the virus initially? Would a longer treatment (maybe taking the drug for six or seven days, instead of five) reduce the risk of the virus coming back?
“Nobody knows,” he said. “Someone should be studying this.”