"What happened is, in the development of the vaccine, as we grow it in eggs, the virus itself mutated a bit, so that there was nearly an accidental mismatch purely on the basis of the virus trying to adapt itself to growing in eggs", Dr. Anthony Fauci told WTOP.
Glaser isn't sure why there were so many cases of the flu here last season, but said severity fluctuates from year to year.
The figure below shows peak flu activity for the United States by month for the 1982-1983 through 2015-2016 flu seasons.
Australia's 10 percent success rate is a major blow to the hopes of Americans lining up for flu shots this year.
Last year, only about 47 per cent of the population was vaccinated in the US.
The Healthcare Foundation donated its remaining 110 vaccines to Public Health, which administers them to schoolchildren for free. The situation in Australia suggests this flu season could be even worse.
Campbell County began reporting flu cases in September and October, which is earlier than past year, Public Health Director Jane Glaser said.
Flu is most unsafe for people over age 65, young children, pregnant women and people with certain health conditions such as asthma or heart disease.
Deti cautions that the county data is often inaccurate because many people do not go to the doctor when they have the flu and those who do often don't get officially tested and diagnosed.
"The very process of how we make the vaccine creates an unanticipated, nearly accidental mismatch, which is what happened in Australia this year", Fauci said in an interview.
A flu shot is a vaccination made of inactive flu strains.
If you're 65 or older, there are two vaccine options created to boost immune response. "Work with your physician to determine the best vaccine type for you, and don't delay in getting medical care if you suspect you have contracted the flu".
The production of universal vaccines entails no such risk.