A Mild Avian Influenza Season Ahead?

Richard Webby, PhD, director of the World Health Organization Collaborating Center for Studies on the Ecology of Influenza in Animals and Birds and Department of Host-Microbe Interactions, Division of Virology, St. Jude Children's Research Hospital is predicting a milder H5N1 (avian) influenza season.

“I think it's clear now that the H5 virus has settled into a bit more of a seasonal pattern where we see this increased activity, increased spillover to poultry to wild mammals, as the migratory birds fly south,” Webby said. “And this time last year, we saw the emergence of what was quite a fit virus, and it spread very widely and infected a lot of birds. And so essentially, that's what that prediction is based on.”

And he says the primary vector, wild birds, have likely built immunity.

Learn more about these animals' migration patterns: Understanding the Importance of Bird Migration as it Relates to Avian Influenza

“We saw a lot of activity last year, so a lot of these wild birds were probably exposed to this virus, and certainly the adult birds and those that didn't succumb to infection build up immunity to it,” Webby said. “So again, theoretically, there should be quite a bit of immunity to the H5 virus in the population this season. And although certainly the season has kicked off and we are seeing infections in poultry and wild species, the idea is that a bit more population immunity is in these wild bird populations—that means there may be a little less virus circulating.” 

Avian Influenza Surveillance

Still virus surveillance is key, and Webby's institution, St. Jude, is a long-time partner with the the World Health Organization (WHO), and he says there are tools and strategies to remain vigilant in monitoring spread and severity of potential outbreaks.

“St Jude Children's Research Hospital is a World Health Organization Collaborating Center within their global influenza program who we've had this designation since 1975. Within the global influenza program, there is a network of laboratories. They're just risk or global influenza surveillance and response system. There are over 130 odd labs now globally who collect information, primarily during the seasonal flu season, and that information is used to make recommendations for the seasonal flu shot. But within those discussions, there's also a lot of work, a lot of information, a lot of data sharing on the zoonotic strains, including the H5.”

Additionally, Webby says they utilize the WHO’s Tool for Influenza Pandemic Risk Assessment (TIPRA).

“It's mirrored on a similar tool that the US CDC has that essentially ranks the relative risk of a lot of these emerging flu strains, including the H5N1,” he said. And so what goes into this tool is a lot of really basic research information on these viruses: What disease do they cause? Is there popular population immunity in humans? How widespread are they in animal populations? All of this information gets funneled into this tool, and it spits out at the other end, a relative ranking of all these threats, ranking both on the likelihood that they'll emerge in humans, and then also, if they do emerge in humans, what the likely impact is.”

Additionally, Webby says they are monitoring for transmission in what types of mammals are contracting the virus and transmission rates, if any, in people.

“If we start to see transmission in some other mammal host, that would give us some concern. Similarly, if we saw an uptick in human cases, that would be obviously very direct evidence that something might be changing. From a more virologic perspective, we're also monitoring the H5 virus as it transmits, not just in the US or the Americas, but other parts of the world as well.

We know some of the molecular markers, meaning, when we sequence these viruses, there are some specific changes in the virus that we know likely increase the threat or the potential risk of these viruses to humans. There's one very clear one, and that is the way in which influenza viruses interact with the host receptors. Even influenza viruses bind to the host receptor, and it's a sugar, but they bind to one form of that sugar. Human adapted viruses bind to that same sugar, but that sugar, they bind to it in a slightly different way, and we know the markers on the virus that modulate that switch, and so that's one thing we're looking for.”

Not only is the potential of a mild season good news, but Webby says the way the virus typically behaves is also encouraging.

“While the H5 virus is circulating in birds, there doesn't seem to be much pressure on that virus to change to be more infectious for humans,” Webby said.