Dr. Susan Detmer, an Associate Professor with the Western College of Veterinary Medicine, is encouraging people in swine production to protect their pigs by getting the annual flu shot.
With the further relaxation of restrictions in Canada, patterns of influenza infection will return to more normal this year, as in the United States last year.
Dr. Detmer said with the lockdown and other restrictions for the pandemic, few influenza viruses circulated in humans in the northern hemisphere, including Canada, Europe, and the United States. So it reduced the number of viruses circulating among the human population. From 2021 through winter 2022, Americans opened up their systems, making it more like an open herd with people moving in and out and travelling with limited restrictions. It created a normal flu season with a strong fall peak around November. And then their winter peak was slightly lower and longer than usual normally seen with the two peaks of influenza activity.
In Canada, producers had more of a closed herd with many restrictions that limited movement in the country and internationally, producing a much lower and later single peak as restrictions from COVID started to open up. But unfortunately, that’s when the movement of influenza viruses increased into and around Canada.
So the key drivers of the respiratory virus circulation being most are aerosol but also in close contact transmitting these viruses. So in-person gatherings are one of the ways they spread within the community, and air travel is how they move between different communities. They also travel on land, but the big one is air travel.
“People travelling a long distance introduce a virus that is not necessarily in that population.” By April, Canada had lifted most of the restrictions and in early fall removed most of those remaining border restrictions.
She said for the first time in a very long time the industry has the best chance of the vaccine matching what is circulating in the population. So last year experts had a 50/50 shot. They had two H3N2 viruses to choose from, and they picked the wrong one. So there was some circulation of that H3N2, more than 80 per cent of worldwide was this other strain of H3N2.
“It’s in the vaccine and 70 to 80 percent of what’s circulating this fall is that H3N2 a good match. The H1N1 is at least 20 per cent of what’s circulating is the derivative or the evolution of the 2009 pandemic, H1N1.”
That H1N1 is still circulating in the human population and the Yamagata lineage Influenza B is all in the influenza vaccine giving good coverage with the vaccine this year.
Dr. Detmer said before the COVID pandemic, the H1N1 virus from the 2009 pandemic was a seasonal strain of flu in humans.
“Every year we saw it and every year as a pig influenza surveillance person, I saw that pandemic strain get into pigs every year.”
Some of what is circulating of H1N1 in pigs is from years ago, but almost half of what she sees annually comes directly from people into pigs. So what’s circulating in the human population of that H1N1 gets into pigs yearly. Last winter, a human-to-pig transmission was the most common H1N1, one of Quebec pigs’ most detected genetic strains. The same thing will happen again this year.
Since pigs have that pandemic-like H1N1 virus circulating and humans are also susceptible to that virus and circulating it, getting the annual flu vaccine protects people from getting serious infections with the strain.
“It helps break the human-to-pig-to-human-to-pig cycle that shows where the virus goes back and forth between the two populations. So for that reason, I recommend you get your flu vaccine and help protect both the human and your pig herd.” •
— By Harry Siemens
