American Society for Microbiology
Each year, scientists create an influenza (flu) vaccine that
protects against a few specific influenza strains that researchers predict are
going to be the most common during that year.
Now, a new study shows that
scientists may be able to create a 'universal' vaccine that can provide broad
protection against numerous influenza strains, including those that could cause
future pandemics. The study appears inmBio, the online open-access
journal of the American Society for Microbiology.
"The reason researchers change the vaccine every year is that they want to specifically match the vaccine to the particular viruses that are circulating, such as H1N1. If the vaccine is just a little bit different to the target virus, it is not expected to offer much protection," said principal investigator of the study Jeffery Taubenberger, MD, PhD, Chief of Viral Pathogenesis and Evolution Section, Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases (NIAID).
"What we
have done is design a strategy where you don't have to think about matching the
vaccine antigen to the virus at all."
In the new study, researchers at the NIAID used a virus-like
particle vaccine cocktail that expressed a handful of different subtypes of a
key surface protein of the influenza virus: hemagglutinin H1, H3, H5 and H7.
"There are 16 different hemagglutinin subtypes that circulate in birds and
are thought to be the basis for current and future influenza pandemics,"
said Dr. Taubenberger.
"The hypothesis was that the presentation of these
different viral proteins would stimulate the development of cross-protective
immunity that would provide broader protection against multiple subtypes."
The researchers picked the H1 and H3 subtypes because they have
been the major cause of human seasonal flu outbreaks since 1918. They chose the
H5 and H7 subtypes because they have been the cause of recent bird flu
outbreaks and have pandemic potential. This selection also provided a broad
representation of hemagglutinins across the phylogenetic tree.
In a series of experiments, the researchers found that 95% of
mice vaccinated with the investigational cocktail were protected against a
lethal challenge with eight different influenza strains expressing seven
different influenza A subtypes, compared to only 5% of mice who received mock
vaccinations.
"Almost all of the animals that were vaccinated survived,
including mice that were challenged with viruses that expressed hemagglutinin
subtypes that were not in the vaccine at all, viruses that expressed H2, H6,
H10, and H11," said Dr. Taubenberger.
"What that suggests is that
this approach really gives us broad spectrum protection, and could serve as a
basis for an effective pre-pandemic vaccine."
Additional experiments showed that the vaccine was durable,
effective for at least 6 months, and that it worked well in older mice. This is
important given that elderly people are particularly susceptible to severe
disease following influenza infection, and current vaccines are less
efficacious in the elderly than in younger people.
"These initial findings are very positive and suggest a
promising and practical strategy for developing a vaccine with amazing, broad
protection," said Dr. Taubenberger.