Unlike traditional vaccines for influenza, the experimental vaccines in both studies focused on the stem of hemagglutinin molecules.
While most flu vaccines utilize the head of a molecule called hemagglutinin on the surface of flu viruses, the new experimental vaccines both utilized the stem of this molecule, which is less prone to mutation than the head.
"The head region of hemagglutinin is what is so variable from year to year and it's why we have to make new vaccines every year to keep up with the changing strains," Dr. Barney Graham told ABC.
Dr. Graham, from the National Institute of Allergy and Infectious Diseases, MD, and colleagues were behind one of the vaccines - a new nanoparticle vaccine for one subtype of influenza. They discovered that the vaccine also offered complete protection from a different flu subtype - known as heterotypic protection - to mice.
The study, published in Nature Medicine, also reveals that the vaccine provided partial protection to the different flu subtype to ferrets.
In order to successfully target the stem region of influenza hemagglutinin, the team produced a stable version of the stem using hemagglutinin taken from an H1N1 influenza virus, also known as swine flu.
The hemagglutinin was then linked to nanoparticles and a substance designed to boost the body's immune response. The researchers then tested the capabilities of the new vaccine by administering it mice and ferrets and then infecting the animals with a potentially lethal dose of H5N1 influenza, also known as bird flu.
While the antibodies produced by the vaccine did not eliminate this strain of influenza, the vaccine did confer protection to the majority of the animals.
The researchers then took antibodies from mice that had survived and injected them into a group of unvaccinated mice to see if they were afforded protection from subsequent H5N1 infection. Again, a majority of the animals survived; although the antibodies did not neutralize the virus, they nevertheless provided protection.
Both experimental vaccines provided heterosubtypic protection
In the other study, published in Science, researchers designed a vaccine candidate that targeted the hemagglutinin stem and was capable of inducing antibodies to fight a range of influenza subtypes.
Vaccine candidates were tested in rodents and monkeys. One of the candidates was found to produce antibodies that bound with the hemagglutinin of numerous influenza subtypes, including H5N1.
The team demonstrated with electron microscopy and X-ray crystallography that their most promising vaccine candidate mimicked the hemagglutinin stem, allowing antibodies to bind with it in the same way that they would with a real virus.
"This study shows that we're moving in the right direction for a universal flu vaccine," reports Ian Wilson, chair of the Department of Integrative Structural and Computation Biology at The Scripps Research Institute (TSRI) in La Jolla, CA.
With both studies, the next steps that need to be taken are ones that will see if these experimental vaccines can work in humans, as well as exploring the mechanisms by which the antibodies provide heterotypic protection.
"While there is more work to be done, the ultimate goal, of course, would be to create a lifelong vaccine," Prof. Wilson confirms.
According to the Centers for Disease Control and Prevention (CDC), seasonal flu leads to over 200,000 hospitalizations and 36,000 deaths each year. While seasonal flu vaccines offer some protection, these require constant updating due to mutations that create a variety of influenza subtypes.
Due to the variability of flu viruses, the CDC reported earlier this year that this season's flu vaccine is only 23% effective across all age groups.