FDA Approves Moderna's mRNA Flu Vaccine; Measles Cases Continue to Rise

The U.S. Food and Drug Administration approved Moderna's influenza vaccine for older adults, making it the first licensed flu shot made from mRNA technology, after the agency reversed an earlier decision to refuse review. The approval came amid ongoing measles outbreaks in the U.S., a new CDC director confirmation, and multiple new health advisories.

The approval capped a process that began in February, when the agency's then-head of biologics issued a rare "refuse-to-file" notice, overruling career staff. A week later, after Moderna disclosed the FDA's decision, the decision was reversed. Earlier, the FDA had declined to review Moderna's biologics license application for its investigational influenza vaccine, issuing a Refusal-to-File letter that hinged on trial design rather than concerns about safety or effectiveness; the agency determined the company used a licensed standard-dose seasonal influenza vaccine as a comparator in a pivotal phase 3 efficacy study, which did not reflect the "best-available standard of care."

A U.S. committee will meet to review measles data and make a recommendation to the Pan American Health Organization about the country's measles elimination status. The committee chair wrote that the case numbers this year "are a runaway train" and "a stark reminder that public health victories can be reversed." The CDC reported 208 confirmed outbreak-associated cases and two deaths in Texas and New Mexico as of March 7, 2025. As of April 9, 2026, the CDC reported 1,741 cases of measles in the U.S., an additional 43 cases week-over-week, a 2.57% increase.

The CDC issued a joint Health Advisory with the White House Office of National Drug Control Policy after reports of increasing detection of medetomidine in the U.S. illegal drug supply, noting exposure may result in profound sedation, bradycardia, and hypotension. The CDC also issued a Health Update on hantavirus testing after an outbreak linked to a cruise ship; as of May 18, no confirmed U.S. cases were associated with the outbreak. An advisory recommended expedited subtyping of influenza A-positive specimens in hospitalized patients amid sporadic human infections with avian influenza A(H5N1). Another advisory was issued after New World screwworm cases were identified in animals in Tamaulipas, Mexico, with no outbreak-related infestations in the U.S. as of January 20, 2026. Updated ACIP recommendations included expanded pneumococcal vaccine use to adults aged 50 and older and pentavalent meningococcal vaccine use in patients aged 10 years and older.

A study published in Nature found that, among patients hospitalized with Covid, reactivation of certain dormant viruses is correlated with disease severity. The study included longitudinal data from more than 1,100 hospitalized Covid patients and found significant reactivation of two virus families during acute infections: Herpesviridae and Anelloviridae. Reactivation of Anelloviridae was strongly associated with long-term physical disability and long Covid, and these reactivations also occurred frequently in "immunocompetent" people, challenging the presumption that this sort of reactivation is concentrated in immunocompromised people.

A cluster-randomized trial in Singapore found that releasing Wolbachia-infected male Aedes aegypti mosquitoes cut dengue risk by over 70%. In a small clinical trial, a fecal microbiome transplant delivered via "stool capsules" increased peanut tolerance in six of 15 participants one month after transplant, with a few lasting four months. The CDC investigated extraintestinal invasive E. coli, the most common pathogen in community-onset sepsis, finding that more than 34% of invasive E. coli infections are resistant to three or more antibiotic classes.

A second child died in a Chinese gene-editing trial; the company HuidaGene disclosed that the trial was shut down when a young boy died after receiving the therapy. The PASTEUR Act was reintroduced in Congress for the fourth time, proposing subscription-style contracts with pharmaceutical companies for critically needed antimicrobials. An amicus brief filed by more than 100 college deans and scholars and multiple professional organizations supports a lawsuit against HHS vaccine policy changes, asserting changes to the pediatric vaccine schedule were made without following ACIP's procedural safeguards. A new CDC director was confirmed, ending a nearly yearlong vacancy in the position.