Combining a vaccine against influenza A with one against pneumococcal bacteria into a single shot makes both more effective, at least in mice. If the success can be replicated in humans, we could be in sight of taming two of the world's most devastating diseases, at quite modest costs.

People call minor colds “the flu”, disguising the fact influenza kills more than a million people a year, even in years without a 1918-type epidemic. Often it does not work alone – combining with the bacterium Streptococcus pneumonia to cause lethal pneumonia.

It was once thought Streptococcus simply took advantage of people's weakened state while their immune system was distracted fighting the virus. More recently, medical researchers have realized the virus and bacteria have a particular affinity, but the reasons are poorly understood. Dr Mohammed Alsharifi of the University of Adelaide has helped with that by showing the synergy works in both directions. When vaccinations are given against both conditions, their interaction makes each more effective, at least in rodents.

Alsharifi is part of a team that has previously invented an influenza vaccine that appears to provide wider protection than those in existence, as well as one against pneumonia. In Nature Microbiology they describe their success when the two were given to mice in a combined shot before the subjects were exposed to both pathogens. “Our findings challenge an age-old immunological dogma about mixing viral and bacterial vaccines in a single injection,” Alsharifi said in a statement.

Alsharifi explained to IFLScience that existing flu vaccines target the proteins on the surface of the flu virus, which mutate frequently. This is why you need a new shot every year and are still only protected against the most common strains. Alsharifi's vaccine builds immune reactions to the surface vaccines, but also develops t-cell function against the inner part of the virus, which is more stable.

It is anticipated this will give the same protection as is currently offered against targeted influenza strains. It also means if someone is infected by a different strain they should clear the virus, and therefore recover, more quickly. By combining this vaccine with one the team developed against pneumococcus, which covers more strains than those currently in use, they boosted the t-cell response even further.

The first human trials are set to start in the next year on the team's pneumococcal vaccine. Alsharifi told IFLScience manufacturing protocols are still being worked out for the flu vaccine. Clinical trials for it, and consequently for the combined dose, will have to wait until these are resolved. When that happens, Alsharifi told IFLScience, it will be the first combined vaccine against a virus and bacterium to be used on humans.