New findings from a team at Philadelphia’s Wistar Institute argue for a change in some types of influenza research.
Historically, ferrets have been the go-to animals in flu vaccine studies.
“The pathology of the virus is very similar to the kind of disease you see in humans, and ferrets can transmit virus from animal to animal,” said Scott Hensley, an assistant professor at the Wistar Institute’s Vaccine Center.
But when it comes to deciding on the strains that make up the seasonal flu vaccine, Hensley and his team have found that ferrets may not always reflect human immune responses.
“Ferrets can really be misleading,” said Hensley. “And that is because the animals that are typically used for these kind of studies are bred specifically for this purpose, and they’ve never seen flu viruses before.”
Hensley’s team is beginning to find that past exposures to flu, either through infection or vaccination, can change how effective a flu shot will be for an individual. Since ferrets have none of that history, using them to evaluate vaccines can mean health officials are more likely to miss important details.
One case where this may have already happened is last year’s flu season. In research published this week in the journal PNAS, Hensley investigated last year’s flu season, in which middle-aged people — not the typical youngsters or older patients — were hit hardest by the circulating virus.
The team identified a mutation in that H1N1 virus that can explain the unusual pattern.
“Middle-aged individuals had antibodies against the H1N1 strain last year, but they just didn’t work that well,” said Hensley. “And that’s because the H1N1 strain has acquired a mutation that basically prevents those antibodies from actually binding to the virus.”
The mutation wasn’t an issue for older and younger people, he said, because they had grown up coming into contact with different flu viruses. But flu viruses that dominated in the ’70s and ’80s ultimately changed how those born between 1965 and 1979 responded to the vaccine. When their immune systems began making antibodies, those molecules targeted the mutated section of the virus and weren’t protective.
Instead of using ferrets, which would never be able to predict this kind of population-level failure, Hensley suggests moving the testing closer to home.
“The best way moving forward is really to go into humans; take human antibodies and incorporate them into the surveillance process,” he said.
By taking samples from many people, Hensley says a flu vaccine could take into account the different flu histories individuals may have.
This year’s flu vaccine includes the same strain of H1N1 as last year — so it’s possible middle-aged folks may again be susceptible. But Hensley said that’s not likely. A flu season with a dominant subtype, such as last year, is usually followed by a different subtype.
While Hensley is focused on making flu vaccines even better, he said they are usually very effective — and important for everyone to get.