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Federal health regulators on Tuesday issued a warning that COVID-19 patients who have taken the antiviral treatment Paxlovid may experience a rebound and test positive again two to eight days after initial recovery. The warning comes more than a month after droves of patients began swapping accounts on social media of COVID rebounds after taking Paxlovid. The alert from the Centers for Disease Control and Prevention said it continues to recommend Paxlovid for patients at high risk for serious complications from infection. It also said that people with a recurrence of COVID-19 symptoms, or a new positive test after having tested negative, should isolate again for at least five days. It added that people should wear a mask for a total of 10 days after rebound symptoms start. (Lazar, 5/24)

The advisory affirmed a trend many patients and doctors have been discussing for at least a month. A case study posted online in late April sequenced virus samples from a 71-year-old man who saw his illness rebound after finishing Paxlovid. The study, which is under review by a medical journal, found no indication that the man had developed resistance to the drug; instead, the authors suggested that symptoms may recur “before natural immunity is sufficient to fully clear” the virus. More recently, three prominent doctors have documented so-called Paxlovid rebounds within their own households on Twitter. (Bendix, 5/24)

A study from Israel published today in BMJ shows that the effectiveness of a fourth dose of Pfizer-BioNTech's mRNA COVID vaccine waned faster than a third dose in adults ages 60 and older. ... To gauge breakthrough infections, the authors performed a matched analysis that compared positive cases to controls by week since vaccination. The added relative vaccine effectiveness of a fourth dose against infection quickly decreased over time, peaking during the third week at 65.1% (95% confidence interval [CI], 63.0% to 67.1%) and falling to 22.0% (95% CI, 4.9% to 36.1%) by the end of the 10 week follow-up period, the authors said. (5/24)

A UK study suggests that COVID-19 vaccination offers protection against infection, hospitalization, and death for most cancer patients but is less effective and wanes faster than in the general population. In the study, published yesterday in The Lancet Oncology, a team led by University of Oxford researchers mined public data on English adults with and without cancer who had received two doses of a COVID-19 vaccine from Dec 8, 2020, to Oct 15, 2021, a period during which the Delta variant became dominant. (5/24)

There are thousands of children across Maryland who not only haven’t been vaccinated against COVID-19, but also lack protection from influenza and the kinds of diseases that routine shots long ago made scarce, such as measles and chickenpox. It’s a worrisome trend for public health experts, who see a surging number of children infected with the coronavirus and fear another outbreak in particular may be on the horizon — measles. (Cohn, 5/25)

Billions of people around the world have now been dosed at least once, twice, or thrice; the shots have saved hundreds of thousands, if not millions, of lives, in the United States alone—and they probably could have saved hundreds of thousands more, had more people rolled up their sleeves. “We’re so much better off than where we were in 2020, when nobody had any immunity,” says Donna Farber, an immunologist at Columbia University. It feels, in some ways, like gazing down the side of a mountain we’ve been trekking up for a good 30 months: A nice, stubborn buffer of elevation now lies between us and the bottom, the sea-level status of no protection at all. The body’s defenses against severe disease are immunological bedrock—once cemented, they’re quite difficult to erode. Even as the fast-mutating virus pushes down from above, our footing has, for more than a year now, felt solid, and the ground beneath us unlikely to give. (Wu, 5/23)

At first, Michelle Rogers thought the Craigslist ad she’d stumbled upon was a scam. It sounded like something out of a science fiction film: Researchers were offering thousands of dollars to volunteers who were willing to give themselves the flu. However strange it sounded, the experiment was the real thing. Vaccine researchers at the University of Maryland School of Medicine were testing just how much exposure to a current strain of influenza would cause infection as a way to prepare for future testing of antiviral drugs and vaccines. (Condon, 5/24)