After year with virtually no flu, scientists worry the next season could be a bad one - NBC News

“We’ve gone over a year without a significant portion of the population getting infected with flu and getting immunity because of that,” Pekosz said.

When someone gets the flu, they usually develop some immunity to the virus.

But since there was such little influenza circulating this year, the number of people without any prior immunity could double.

“With low level population immunity, that could bring about more cases,” said Scott Hensley, a microbiologist at the University of Pennsylvania Perelman School of Medicine.

It’s unclear whether there are actually fewer strains circulating, or if there has just been limited sampling of the virus because there have been so few cases, meaning it may be possible other strains are out there that haven’t been detected.

Which of these scenarios turns out to be the case could have a significant impact on next season’s flu vaccine, which is made yearly to protect against the most prominent virus strains circulating around the globe.

If there are truly fewer strains circulating, then the vaccine stands a better chance of being a good match, making it more effective.

“There could be strains circulating at a low number that could come to dominate.

The World Health Organization selected the strains for the next flu vaccine in February, based on what’s been circulating around the globe.

Scientists often pay particular attention to strains in the southern hemisphere, where flu season starts in June and typically peaks in August.

“The pattern of influenza activity in the Southern Hemisphere prepares the Northern Hemisphere for what may happen in their next season,” said Kanta Subbarao, director of the WHO Collaborating Centre for Reference and Research on Influenza.

“Often new viruses that are first noted in the Southern Hemisphere spread and become the dominant strain in the Northern Hemisphere.”.