Early Flu, Late RSV: What Infection Preventionists Should Watch This Respiratory Season

An early wave of influenza is being driven by a mutated H1N1 strain that only partly escapes population immunity, and this season’s vaccine still appears to recognize it, an influenza virologist said.

Meanwhile, the new messenger RNA (mRNA) influenza vaccine will be watched through the same passive and active safety surveillance that covers every vaccine, said a vaccine researcher. Recipients may notice more side effects than with traditional shots.

“However, data suggests this year’s influenza vaccine can recognize this variant, so the immune escape is only partial or rather incomplete,” said Andrew Pekosz, PhD, professor and vice chair of the W. Harry Feinstone Department of Molecular Microbiology and Immunology at the Johns Hopkins Bloomberg School of Public Health and co-director of the Johns Hopkins Center of Excellence in Influenza Research and Response.

Pekosz spoke during an Oct. 29 media briefing hosted by the Bloomberg School with Anna Durbin, MD, professor in its Department of International Health and director of the Johns Hopkins Center for Immunization Research. The experts answered questions from multiple news outlets, including Infection Control Today.

What do surveillance data show?

The CDC reported almost 5,000 laboratory-confirmed influenza hospitalizations nationwide during the week ending Oct. 17, the highest early-season rate for mid-October since the 2010-2011 season, Durbin said.

Activity is low but increasing, particularly in the West and South, Pekosz said. The H1N1 variant carries new mutations compared with last year’s virus, so some mismatch with the vaccine is expected, but preliminary CDC data show antibodies generated by the current vaccine recognize it. H1N1 accounted for 125 of 127 subtyped influenza A viruses in CDC surveillance for the week ending October 3.

The vaccine’s other 2 components look like good matches for strains expected later, and early efficacy estimates should come in early December, Pekosz said.

How will the mRNA vaccine be monitored?

Every vaccine is subject to passive surveillance, in which anyone can report an adverse event to the Vaccine Adverse Event Reporting System, Durbin said. Health care systems and other networks also run active surveillance, searching for cases of adverse events.

“So there’s not necessarily anything special for this new mRNA vaccine, these surveillance activities are going on all the time, but it is carefully looked at,” Durbin said.

The mRNA vaccine can cause body aches and pains and a low-grade fever, and it probably has more side effects than traditional influenza vaccines, she said. Licensed for people 50 and older, it outperformed traditional vaccines in clinical trials in that age group.

“Its safety profile is really strong, and it is an option that’s available for people that, at least the preliminary data suggests, could be better in terms of protecting you from severe disease,” Pekosz said.

Who needs a protective shield?

Immunocompromised people and adults 65 and older should get vaccinated, and older adults have higher-dose vaccines, Durbin said. Health systems have options there: a large real-world study found comparable effectiveness between adjuvanted and high-dose vaccines in older adults, Infection Control Today reported.

Many older adults are infected by grandchildren and other children, so vaccinating the people around high-risk patients matters, Durbin said.

“That’s really sort of giving a nice shield around the people to help prevent them from getting influenza,” Durbin said.

How can patients tell the viruses apart?

Trouble breathing suggests infection is moving deeper into the lungs and is probably not a cold, Pekosz said. Home tests can identify influenza, COVID-19 and respiratory syncytial virus (RSV), which matters for high-risk patients because influenza and COVID-19 antivirals work only if started within a few days of symptom onset.

Which vaccines should be reviewed now?

Asked by Infection Control Today how often younger adults need pneumococcal vaccination, Pekosz said pharmacies can provide the recommendations. His broader advice was to ask about every eligible respiratory vaccine at once.

“This is the time of year where all of those vaccines against respiratory infections should be looked at, and you should think about getting updated for them if you’re eligible to provide the most protection just before the season starts,” Pekosz said.

COVID-19 activity is low but steady, with a surge expected in December and January. RSV has been unusually quiet, though Pekosz expects it within weeks. Flu and COVID-19 vaccines can be given together, Durbin said. Amid shifting federal guidance, Pekosz closed with a reminder.

“Vaccines are the best protection, and getting vaccines early ensures you get the most protection out of those vaccines,” Pekosz said.