Some patients who appear to recover from COVID-19 after taking Pfizer's antiviral, Paxlovid, experience a relapse in symptoms soon after — the latest phenomenon researchers and physicians are racing to understand, The Wall Street Journal reported May 10.
"This is something public health agencies will have to wrap their heads around and figure out what to do," said Michael Charness, MD, chief of staff at the VA Boston Healthcare System.
Six details:
1. Anecdotal reports of patients who seemed to recover after taking a five-day course of Paxlovid and then experienced a rebound in symptoms within two weeks first made headlines in April. The phenomenon gained traction after patients and physicians took to social media platforms to detail their cases, with some saying patients tested positive again after the rebound, despite feeling better and testing negative days earlier.
2. It's unclear how common the rebounds are, though officials from Pfizer and the FDA said about 2 percent of 1,120 participants in the Paxlovid trial who took the drug experienced rebounds between 10 and 14 days after starting treatment. This figure, however, was comparable to the 1,126 who received a placebo, suggesting the phenomenon is not caused by the medication, a Pfizer spokesperson told The Wall Street Journal. A spokesperson for the National Institute of Allergy and Infectious Diseases told the news outlet the institute is planning to examine how often rebound cases occur, why they occur and whether extending treatment helps prevent this.
3. An FDA official in a May 4 interview said there is "no evidence of benefit at this time for a longer course of treatment … or repeating a treatment course of Paxlovid in patients with recurrent COVID-19 symptoms," for those who've taken a five-day course of the treatment. This conflicts with comments from Pfizer's CEO, Albert Bourla, who told Bloomberg a day earlier that a second course can be given for the rare cases in which people experience rebound symptoms.
4. Health experts aren't sure whether those experiencing a subsequent round of symptoms after completing a course of Paxlovid treatment are contagious. Some physicians who have seen patients with symptom rebounds have recommended they restart isolation.
5. Some health experts theorize the relapses occur because the drug is taken too early in the course of disease, which prevents the immune system from mounting a full response to keep the infection from progressing. Another theory researchers shared with the Journal is that Paxlovid isn't in the body long enough for it to fully stamp out the virus in some people.
6. The treatment in Pfizer's trial reduced the risk of hospitalization or death by 89 percent in adults with COVID-19 who were considered at high risk of developing severe illness. FDA officials have said reports of rebound cases "do not change the conclusions from the Paxlovid clinical trial, which demonstrated a marked reduction in hospitalization and death."