An experimental mRNA-based vaccine against all 20 known subtypes of flu viruses provided broad protection against otherwise lethal flu strains in initial tests, according to a study.
This could one day serve as a general preventive measure against future flu pandemics, said researchers from the University of Pennsylvania, US.
According to the study, tests in animal models showed that the vaccine dramatically reduced signs of illness and protected against death, even when the animals were exposed to strains of flu other than those used to make the vaccine.
The “multivalent” vaccine, which the researchers described in a paper published in the journal Science, used the same messenger ribonucleic acid (mRNA) technology used in the Pfizer and Moderna SARS-CoV-2 vaccines, according to the study .
This mRNA technology that enabled these Covid-19 vaccines was pioneered at Penn, according to the study.
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“The idea here is to have a vaccine that gives people a basic level of immune memory to various strains of flu, so there will be far less illness and death when the next flu pandemic occurs,” the author said. studio principal Scott Hensley.
Influenza viruses periodically cause pandemics with enormous death tolls. The best known of these was the “Spanish flu” pandemic of 1918-19, which killed at least tens of millions of people worldwide.
Influenza viruses can circulate in birds, pigs and other animals, and pandemics can start when one of these strains jumps into humans and acquires mutations that make it better suited to spread among humans.
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Current flu vaccines are only “seasonal” vaccines that protect against recently circulating strains, but are not expected to protect against new pandemic strains. The strategy employed by the Penn researchers is to vaccinate with immunogens, a type of antigen that stimulates immune responses, from all known subtypes of influenza in order to obtain broad protection, according to the study.
The vaccine is not expected to provide “sterilizing” immunity that completely prevents viral infections. Instead, the new study showed that the vaccine elicited a memory immune response that can quickly remember and adapt to new pandemic viral strains, significantly reducing severe illness and death from infection.
“It would be comparable to the first-generation SARS-CoV-2 mRNA vaccines, which were targeted at the original Wuhan strain of the coronavirus.
“Unlike later variants such as Omicron, these original vaccines did not completely block viral infections, but they continue to provide long-lasting protection against severe disease and death,” Hensley said.
The experimental vaccine, when injected and absorbed by recipient cells, began to produce copies of a key flu virus protein, the hemagglutinin protein, for all twenty flu hemagglutinin subtypes: H1 to H18 for influenza A viruses and two more for influenza B. viruses.
“For a conventional vaccine, immunizing against all these subtypes would be a big challenge, but with mRNA technology it’s relatively easy,” Hensley said.
In mice, the mRNA vaccine elicited high levels of antibodies, which remained high for at least four months and reacted strongly to all 20 influenza subtypes. In addition, the vaccine appeared relatively unaffected by prior exposures to the flu virus, which can bias immune responses to conventional flu vaccines.
The researchers observed that the antibody response in the mice was strong and broad, whether the animals had been previously exposed to the flu virus or not.
Hensley and his colleagues are designing human clinical trials, he said. The researchers anticipate that if these trials are successful, the vaccine may be useful in eliciting long-term immune memory against all subtypes of influenza in people of all age groups, including young children.
“We think this vaccine could significantly reduce the chances of getting a serious flu infection,” Hensley said.
In principle, he added, the same multivalent mRNA strategy can be used for other viruses with pandemic potential, including coronaviruses.