• Posted April 30, 2026

Nasal Spray Flu Vaccines Create 'Battlefield' In Adults' Noses

Nasal spray flu vaccines appear to work differently from traditional jabs, creating a battlefield in the nose for invading viruses, a new study says.

The FluMist vaccine triggers an immune response directly in nasal tissue in adults, researchers reported April 29 in the journal Science Translational Medicine.

This immune response stays in the upper airways and can’t be detected in blood samples, which has hidden the nasal vaccine’s potential benefits in adults, researchers said.

“The general thinking was that the FluMist vaccine didn't do much of anything in most adults," said senior researcher Shane Crotty, chief scientific officer for the La Jolla Institute for Immunology in California.

"But we've shown that actually, surprisingly the majority of people actually are responding to the vaccine directly in their nasal tissues,” he said in a news release.

FluMist has proven effective in children and is licensed for adults, but scientists had found no sign of influenza-fighting immune cells circulating in adults’ blood after they got the nasal vaccine.

That made experts question whether the nasal vaccine could protect against the flu, researchers said.

For the new study, researchers tapped into the immune cells of the nasal passages, using a new deep nasal swab technique to gather specimens for study.

They found that immune cells in the upper airways respond quickly to viral infections, and even carry memories of past infections that could be used to fend off new ones. This activity was only detectible in the upper airways, not the bloodstream.

In nasal swabs collected from 25 adults before and after they received FluMist, researchers found a dramatic increase in flu-fighting immune cells in their upper airways.

This response was durable, with immune cells remaining active in the nasal passages six months following vaccination, researchers said. However, these cells were only in the nose, and weren’t circulating in the blood.

“This really speaks to the point that if you only look in the blood following an intranasal or a mucosal vaccination, you probably are missing some really interesting immunology," lead researcher Hannah Stacey, a postdoctoral researcher with the La Jolla Institute, said in a news release.

The team compared these findings to 25 adults who got a regular flu jab, and found that their immune response was completely different.

The injected vaccine increased flu-fighting antibodies in the bloodstream, but did not create a protective immune cell response in the upper airways, the study found.

Researchers emphasized that these findings don’t mean that FluMist works as well as the usual jab. They are still determining whether the nasal immune cell response is strong enough to offer lasting protection against the flu.

In the meantime, these results could help better judge the effectiveness of new types of nasal vaccines, researchers said.

"Let's say you have a new intranasal vaccine, and you want to test the effectiveness of four different doses," Crotty said. "You can use the deep nasal swabbing technique to compare vaccine responses in small groups of people. Then you could make a science-based decision for which vaccine should move forward. This could really speed up future vaccine development for needle-free vaccines.”

More information

The U.S. Centers for Disease Control and Prevention has more on nasal spray flu vaccines.

SOURCES: La Jolla Institute for Immunology, news release, April 29, 2026; Science Translational Medicine, April 29, 2026