Aug. 22 (UPI) -- A candidate for a universal flu vaccine has displayed significant success for various virus strains in animals.
Researchers at the Perelman School of Medicine at the University of Pennsylvania found the vaccine had a strong antibody response to a structure on the surface of several flu viruses, called the hemagglutinin stalk. The findings were published Wednesday in the journal Nature Communications.
"If it works in humans even half as well as it does in mice, then the sky's the limit -- it could be something that everyone uses in the future to protect themselves from the flu," Dr. Scott Hensley, an associate professor of microbiology at Penn, said in a press release.
Currently, flu vaccines need to be developed each year for a particular strain.
Unlike seasonal flu vaccines, a universal flu vaccine could be given a few times over a lifetime to provide protection potentially similar to a tetanus vaccine.
"This vaccine was able to do something that most other candidate flu vaccines have not been able to do,"study co-senior author Dr. Drew Weissman, a professor of infectious diseases, said. "It was able to elicit protective responses against a conserved region that offers broad protection."
Viral vaccines typically use lab-grown viral proteins to elicit an immune response for protection against future exposures to a virus. But this approach, researchers said, hasn't worked well against influenza viruses.
Because flu virus particles have mushroom-like HA proteins, seasonal flu vaccines use them to elicit antibody responses. But these antibody responses are almost entirely directed against the outermost "head" region of the HA proteins, which mutate rapidly. Also, strains of flu prevalent in one flu season are often replaced by other strains with different HA head structures in the next flu season.
Rather than using HA proteins, the universal vaccine candidate uses mRNA molecules that encode HA proteins to elicit an antibody response. They better mimic a real flu infection and powerfully protect an antibody response.
"When we first started testing this vaccine, we were blown away by the magnitude of the antibody response," Hensley said.
After immunization, these strong antibody responses lasted the entire 30 weeks of the experiment. In fact, they were even stronger than after four weeks.
The researchers successfully repeated these experiments in ferrets and rabbits.
In further tests in mice, they found a vaccine encoding the H1 subtype worked against three flu strains: the same H1 flu virus, a distantly related H1 flu virus and an H5 strain.
"The next step is to test this in non-human primates and humans," Hensley said.
"If we were to combine our vaccine approach with newly developed HA stalk antigens, it would probably lead to a really good universal vaccine."
Researchers are planning clinical trials in humans within two years.
In 2017, the Penn researchers were able to protect mice and monkeys against Zika with a single injection of an mRNA vaccine.
In February, the National Institute of Allergy and Infectious Diseases announced a goal of a safe and effective universal influenza vaccine that is at least 75 percent effective, protects against group I and II influenzas, protects for at least one year and works for all age groups.