“People who experience a relapse are at risk of infecting others, even outside of what they would consider a normal window,” said Dr. Michael Charness of the Veterans Administration Medical Center in Boston.
Charness and his colleagues recently collaborated with a team of researchers at Columbia University to study cases of Covid-19 that have returned after treatment with Paxlovide. He said they found at least two cases where people became infected when they had sources of infection.
In one case, a 67-year-old man became infected with a 6-month-old boy while he was with the child half an hour later.
This person is 12 days after their first positive Covid-19 test. He completed a five-day course of Paxlovid and felt better. She had no symptoms when she saw her granddaughter, but about eight hours later, she started to feel sick again.
After three days of the baby, both his parents were tested. Neither the baby nor his parents had any other close contact before the illness.
“This suggests that you can be contagious during rebound before symptoms appear,” Charness said. “You know, we studied a small number of people. It’s understandable that there are other people out there who don’t have symptoms and still have viral resurgence.”
In another case, a 63-year-old man infected two family members during a three-day relapse after Paxlovid.
Take precautions after Paxlovid
The CDC said people who test positive again and whose symptoms return after taking antiviral pills should restart the isolation period and self-isolate for five days. According to the agency, people can end the isolation period after this additional five days when their fever goes 24 hours without antipyretics and they feel better. The agency also recommends that people wear a mask for 10 days after symptoms return.
The results and indications for the use of Paxlovid have increased in the United States. Over the past two months, prescriptions filled for Paxlovid have increased from 27,000 to 182,000 per week, according to the White House.
The administration hopes to ramp up the testing-for-treatment program by creating one-stop centers at grocery and drug stores where people can get tested for Covid-19 and immediately pick up and fill prescriptions for antiviral drugs. Antiviral medications should be taken within the first few days of symptoms.
For this reason, the CDC says early treatment with this drug is still recommended.
As helpful as it may be, researchers say people should be aware that the drug may not completely eradicate the infection.
Charness and his co-authors collected at least 10 cases of Covid-19 recurrence after Paxvid. Half of them came from just two families, which the researchers concluded is not uncommon.
Genetic testing shows that when people get a second round of Covid-19 after Paxlovid, it’s not because they’re infected with other strains of the virus. There is also no indication that the virus has changed or mutated to develop any resistance to the drug.
So far, recovery times have been mild. There were no reports of severe illness during the Covid-19 outbreak. Because of this, the CDC says there is no reason to think additional treatment is necessary.
The reason is still unknown
Why this happens remains a mystery.
In his research, Charness said, researchers found that the amount of virus in a person’s body and their viral load decreased when they were treated with Paxlovide.
“People use Paxlovid, and what we know is that it blocks the replication of the virus,” he said. Thus, the level of the virus decreases. But then in some people — no one knows how many because not enough people have been studied — viral levels start to rise again 9 to 12 days after they first test positive, Charness said.
It is unclear whether this rebound is related to Paxlovid. In a study of more than 2,200 Covid-19 patients, Pfizer, the company that makes the drug, said there were a few patients who returned after testing negative for Covid-19, but they were in the group receiving Paxlovid. also suggests that in those receiving a placebo, Covid will recur in some people, even without treatment.
Charness’s team conducted their own comparative study and found something different. When researchers looked at 1,000 Covid-19 diagnoses in National Basketball Association players and support staff who did not take the medication from December to March, they found no cases of Covid-19 returning. This study is still unpublished.
They say more research is needed to understand whether the drug has any connection.
Charness said the recurrence of the infection after treatment raises some questions. First, in people who start the medication later, maybe four or five days after the first symptoms, their immune systems may appear normal after they have had time to first see the virus? Would a longer course of treatment, perhaps taking the drug for six or seven days instead of five, reduce the risk of the virus coming back?
“No one knows,” he said. “Someone should be looking into this.”