Could One Vaccine Replace Three? Early Flu, COVID, RSV Shot Shows Promise, New Study Says

Every fall brings the same routine: rolling up a sleeve for a flu shot, maybe scheduling a separate COVID booster, and worrying whether RSV will land a grandparent or a newborn in the hospital before spring. Three viruses, three appointments, three headaches. A new animal study points to a way to fold all of that into a single experimental shot, one that raised immune responses in mice, ferrets, and cotton rats and protected them against flu, COVID-19, and RSV at the same time.

Researchers of the study, published in the journal Science Advances, built one vaccine designed to take on influenza, SARS-CoV-2 (the virus behind COVID-19), and respiratory syncytial virus, better known as RSV. In the animal tests, that single shot produced protective immune responses against all three, with antibody levels that matched what the animals got from vaccines aimed at just one virus at a time. Bundling the targets together, in other words, did not force the immune system to pick favorites.

Together, these three viruses drive a large share of respiratory illness and death worldwide every year. Vaccines already exist for each one, and scientists have chased the idea of merging them into a single dose for a long time. That goal has been far easier to describe than to build, especially with older protein-based vaccine technology.

How One Shot Could Replace the Flu, COVID, and RSV Vaccine Lineup

Most long-standing vaccines, including the yearly flu shot, are what scientists call subunit vaccines. Instead of using a weakened or killed virus, they deliver just one piece of it, usually a protein the immune system can learn to spot. Subunit shots carry a strong safety record, but packing several unrelated viruses into one of them has been a stubborn technical problem.

Newer approaches, such as the mRNA technology behind some COVID-19 shots, have shown early promise at hitting more than one virus at a time. Protein-based vaccines had fallen behind in that contest. Researchers here tried to close the gap using a nanoliposome, a microscopic bubble of fat that resembles the outer layer of a human cell and can carry proteins on its surface. It works something like a small bulletin board, pinning up wanted posters for several viruses so the immune system can study each face and remember it.

What the Combination Vaccine Puts on a Single Particle

Onto each particle, the team attached several distinct viral proteins. For influenza, they used the surface proteins the flu virus relies on to grab onto human cells, taken from three seasonal flu strains. For COVID-19, they added the part of the spike protein the virus uses to break into cells. For RSV, they included a version of a protein called F, frozen in the shape it holds before infection, a form researchers consider especially good at rousing the immune system. All of it rode on one nanoliposome, a single particle carrying the fingerprints of three viruses.

How the Flu, COVID, and RSV Vaccine Held Up in Animal Tests

To see whether the stacked design worked, researchers tested it in mice, ferrets, and cotton rats, three animals often used in respiratory virus studies because their airways and immune systems react to these infections in telling ways. Animals received two doses a few weeks apart, then met live virus so the team could measure real protection rather than antibodies alone.

Across all three species, the combined shot triggered protective responses against every virus, with antibody levels on par with single-target vaccines. Vaccinated mice survived doses of flu and COVID-19 that killed unvaccinated animals, and their lungs stayed largely clear of virus. In ferrets, flu protection roughly matched Flublok, a licensed commercial flu vaccine the team used as a benchmark.

RSV carried a cautionary backstory. A formalin-based RSV vaccine from the 1960s famously backfired, worsening illness in children who later caught the virus and setting the field back for decades. In the cotton rat tests, the new combined shot protected the animals’ lungs and, unlike that older vaccine, did not appear to inflame lung tissue, a sign the design sidestepped the earlier trap. Bundling everything onto one particle, again, did not measurably weaken the response to any single virus.

Why a Three-in-One Shot Matters Beyond Convenience

Fewer pharmacy trips would be the obvious selling point, but the potential reach runs deeper. Vaccination rates for respiratory viruses stay stubbornly low; as of late 2024, U.S. figures put adult flu coverage near 35 percent and COVID-19 boosters at roughly 18 percent. One reason people skip doses is the sheer number recommended, a burden that falls hardest on older adults and young children already juggling crowded medical schedules. A single shot covering all three could ease that math, if it ever clears human testing.

There is a scientific payoff as well. A traditional protein platform that can juggle three major respiratory viruses at once, and hold its own against single-virus shots in animals, invites an obvious question: what else could it carry? Flu, COVID, and RSV are not the only respiratory threats, and a flexible particle that displays several viral proteins could be updated as new ones appear.

For now, all of this lives in the lab. The vaccine has not been tested in people, and results in animals do not always hold up in humans. Even so, an experimental shot that took on flu, COVID, and RSV together, and performed on par with the individual vaccines, nudges a long-wanted idea a real step closer to the doctor’s office.

Disclaimer: This article describes early-stage research conducted in animals (mice, ferrets, and cotton rats). The vaccine has not been tested in humans, and results in animals do not always translate to people. Nothing here is medical advice. For guidance on flu, COVID-19, or RSV vaccination, consult a licensed healthcare provider.

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