What to watch this respiratory season, from H1N1 to mRNA vaccines

Influenza hospitalizations reached their highest mid-October level since the 2010-2011 season, a Johns Hopkins vaccine expert said, citing the Centers for Disease Control and Prevention (CDC). COVID-19 and respiratory syncytial virus (RSV) are expected to rise in the coming weeks and months.

An influenza virologist said the early wave is driven by a mutated H1N1 strain that partly evades existing immunity. This season’s vaccine still appears to recognize it, and real-world effectiveness data should begin to arrive in early December.

Anna Durbin, M.D., professor in the Department of International Health at the Johns Hopkins Bloomberg School of Public Health and director of the Johns Hopkins Center for Immunization Research, and Andrew Pekosz, Ph.D., professor and vice chair of the W. Harry Feinstone Department of Molecular Microbiology and Immunology and co-director of the Johns Hopkins Center of Excellence in Influenza Research and Response, spoke during an Oct. 29 media briefing hosted by the Bloomberg School. They answered questions from multiple news outlets.

“Influenza can be a very serious illness, and the CDC reported almost 5,000 laboratory-confirmed influenza hospitalizations nationwide during the week ending October 17th. This is the highest early season hospital rate for mid-October since the 2010-2011 flu season,” Durbin said.

What’s driving the early cases?

Activity is rising fastest in the West and South, Pekosz said. The H1N1 variant behind early cases carries new mutations compared with last year’s virus, and some mismatch with the vaccine is expected. But preliminary CDC data indicate antibodies generated by the current vaccine still recognize it, he said. The vaccine’s other two components look like good matches for viruses emerging early.

Washington and California will likely report the first efficacy data, around early December, he said.

When will COVID-19 and RSV arrive?

COVID-19 activity is low but steady, and Pekosz said he expects a surge in December and January. RSV has been largely absent so far.

“We haven’t seen much RSV activity this year, which is a little bit odd. We usually see RSV before we see flu, but again, I expect that we will be seeing RSV in the next couple of weeks,” Pekosz said.

This season’s COVID-19 and RSV vaccines are good matches for circulating viruses, he said. For leaders planning staffing and beds, the experts’ outlook points to overlapping waves rather than one peak.

Could mRNA change the vaccine calendar?

A new messenger RNA (mRNA) influenza vaccine, licensed for people 50 and older, performed better than traditional vaccines in clinical trials in that age group, Durbin said. Whether that holds in the real world is unknown.

Its larger strategic promise is speed, she said. The U.S. Food and Drug Administration (FDA) meets every March to choose vaccine strains because traditional vaccines take a long time to make.

An mRNA vaccine could be updated much faster, potentially after a second strain-selection meeting in July or August if a new strain emerged over the summer. FDA is discussing that possibility, but much depends on the evidence the new vaccine generates, Durbin said.

“We are not there yet,” Durbin said.

What does the coverage question mean?

Durbin said the administration fired the previous members of the Advisory Committee on Immunization Practices (ACIP). ACIP has added new members but has not met in 2026 due to legal challenges of the member appointments and recommendations. When ACIP recommends a vaccine, insurers must cover it. Without a recommendation, insurers are not necessarily required to pay for the mRNA vaccine, which costs more than $100, and that could limit uptake, she said. Industry trade group AHIP has said member plans will keep covering ACIP-recommended immunizations through 2027.

Health systems also have flexibility among existing options for older adults. A large real-world study found comparable effectiveness between adjuvanted and high-dose vaccines in adults 65 and older.

Where do health systems fit in safety monitoring?

Beyond passive reporting, health care systems and other networks actively search for vaccine adverse events, Durbin said. The mRNA vaccine probably causes more side effects than traditional shots, such as body aches and low-grade fever, but monitoring is designed to catch anything unexpected.

Clinicians in those systems remain the key messengers. Margot Savoy, M.D., of the American Academy of Family Physicians told Chief Healthcare Executive that doctors can’t be vague on vaccines and offered guidance for health systems countering skepticism. Durbin made a similar point.

“What I encourage people to do is talk to your physician. If you have a good relationship with your physician, if you have questions about whether or not you should be vaccinated against influenza, or have questions about the vaccines themselves, talk to your physician. A conversation can go a long, long way,” Durbin said.