Paxlovid is Pfizer’s antiviral drug used to treat COVID-19. (Portal/Wolfgang Rattay/Illustration)
When the antiviral drug Paxlovid was approved to treat COVID-19 in 2021, doctors noticed a confounding trend in some of the patients taking it: a rebound case of the virus. After treatment, some people recovered and tested negative for the virus, only to test positive or have symptoms reappear a few days later. “Paxlovid Rebound,” as it is known, received a lot of media attention when President Biden and First Lady Jill Biden and Dr. Anthony Fauci and Rochelle Walensky, director of the Centers for Disease Control and Prevention, all experienced it after taking the drug last year.
Scientists aren’t sure why this rebound effect occurs after taking Paxlovid, but here are a few things we do know.
What is Paxlovid? How does it work?
Paxlovid is an oral antiviral pill that can be prescribed to people who have COVID-19 and are at risk of developing a serious illness. This can be people who are not vaccinated, the elderly or people with other conditions such as cancer or diabetes. The drug developed by Pfizer can protect these high-risk patients from hospitalization. Those who have been vaccinated but are at risk of serious consequences from COVID-19 may also benefit from taking Paxlovid.
US regulators granted emergency use approval to Paxlovid in December 2021. Today, the drug is only available on prescription from a doctor or pharmacist. Anyone age 12 and older who weighs at least 88 pounds and is at high risk for serious medical conditions is eligible for the drug. However, patients with severe kidney disease — or those on dialysis — or people with severe liver disease should not take it. The drug can also interact with other drugs, e.g. B. with drugs to treat high cholesterol, high blood pressure and migraines. Therefore, patients taking these drugs should avoid taking Paxlovid.
Like many antivirals, Paxlovid works best when taken early in the course of the disease. The CDC recommends that treatment begin within the first five days of the onset of symptoms. Once a person has been prescribed the drug, they take three Paxlovid pills twice a day for five days for a full course that adds up to 30 pills.
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Antiviral therapy consists of a combination of two oral antiviral drugs – nirmatrelvir and ritonavir – that work together to stop the viral replication process. By reducing a person’s viral load, the drug decreases the severity of their symptoms.
In clinical trials conducted when the delta variant was predominant, Paxlovid was found to reduce the risk of hospitalization or death in high-risk individuals by 89%. Since its approval, many clinical studies conducted worldwide have also confirmed its high level of protection against hospitalization and death.
Because Omicron is a highly immune-avoidable variant that has rendered many antibody treatments ineffective, vaccine experts feared Paxlovid would also lose its effectiveness. Fortunately, that doesn’t seem to be the case. According to recent research, the drug continues to provide significant protection against hospitalization and death, and may also provide significant benefits to vaccinated patients diagnosed with COVID-19.
However, other studies have found no evidence that Paxlovid benefits people under the age of 65.
“I don’t think we need to use Paxlovid in every 20-year-old who gets COVID or 35-year-old who is healthy,” said Dr. Bruce Farber, chief of public health and epidemiology at Northwell Health, the largest health system in New York state, told Yahoo News. “But in high-risk patients, the elderly, the unvaccinated, comorbidities, the immunocompromised, [for] these people [it] can make a big difference.”
Paxlovid not only prevents high-risk patients from becoming very ill, it may also reduce the risk of symptoms of a long COVID, a study conducted by the Department of Veterans Affairs found in November.
What is Paxlovid Rebound?
The CDC defines a Paxlovid rebound as an occurrence when a person either experiences a recurrence of symptoms after completing the full five-day course of treatment or tests positive after testing negative for COVID-19. According to the CDC, this rebound effect typically occurs between two and eight days after initial recovery. But experiencing a rebound, the agency said, doesn’t mean a person was resistant to Paxlovid, nor does it mean they’ve been reinfected with the virus. Additionally, the CDC has said that Paxlovid rebound cases are typically mild and resolve within a few days, and there is no evidence that additional treatments are needed for these patients.
Despite the effectiveness of Paxlovid itself as part of Omicron, the drug is underutilized in the US and other parts of the world. US doctors have prescribed the drug in only about 13% of new COVID-19 cases, according to a report by London-based health analytics firm Airfinity. Experts have said that concerns about a possible Paxlovid rebound could be one of the reasons.
Farber said another reason for under-utilization of Paxlovid has to do with the virus itself. “This virus is much less virulent, although it’s more contagious,” he said, adding that the need for Paxlovid “has decreased.”
Scientists are still investigating why the rebound effect occurs when taking Paxlovid and who is more likely to experience it. However, recent research has found that people who develop COVID-19 and are not taking Paxlovid can also experience a rebound. Studies are underway to understand why this happens, Farber said.
“Recent data suggest that rebound is also occurring in people who recover from COVID without having received Paxlovid, at likely similar rates whether or not they are taking Paxlovid,” Farber said, adding that rebound cases occur after taking the drug was originally thought to occur in about 5% of cases, but this research has shown that it may be more common than originally thought. “Recent articles say it can happen 10 or 15 percent of the time,” he said.
What to do if you experience a Paxlovid rebound?
If someone’s symptoms return or test positive after Paxlovid treatment, the CDC recommends following isolation guidelines and re-quarantining for five days. Isolation can be ended after this period if a person has been free of fever for 24 hours without any antipyretic medication. The agency also recommends wearing a mask for 10 days after rebound symptoms begin.
The CDC encourages physicians and patients to report Paxlovid rebound cases to the Pfizer portal for adverse events related to the drug.
Finally, Farber said that a Paxlovid rebound is still fairly uncommon and that it shouldn’t put people and their doctors off using the life-saving drug when needed.
“Theoretically, it could prolong their isolation. But I think [people] should be aware that this can also occur without Paxlovid. So it’s really not going to be a major differentiator of whether they get it or not,” he said.