Vaccines are the most important tool we have to control influenza, says Montserrat Torremorell, DVM and professor in the Department of Veterinary Population Medicine at the University of Minnesota.

That’s why her team is continually trying to understand how this respiratory virus is transmitted and maintained in farms today and how vaccines can help prevent transmission.

“We are always interested in how to control influenza better,” Torremorell says. “When we look at control, vaccination is what comes to mind as the most common strategy. Traditionally we have used inactivated or killed vaccines, but more recently we had a live attenuated vaccine commercialized in the U.S. We want to understand how live attenuated vaccines, existing or under development, can contribute to the influenza control.”

In a recently published article in Plos One, Torremorell and her team took a deeper look at the ability of live attenuated vaccines to transmit and infect other pigs. Researchers investigated the transmission of a live attenuated influenza vaccine (LAIV) and found that vaccinated pigs can only spread low levels of influenza A to non-vaccinated pigs — through both direct and indirect contact — for up to six days after vaccination.

How did the pigs respond?

LAIV vaccines use a weakened form of the influenza A virus to create a strong, long-lasting immune response, she explains. The researchers set out to help establish the safest and most effective way to vaccinate herds with these vaccines. They investigated when, where, and for how long LAIV-vaccinated pigs shed small amounts of the virus after vaccination.

“We wanted to see whether vaccinated pigs in a litter would be able to transmit virus to other unvaccinated pigs they were in contact with in the litter, or to unvaccinated pigs separated in a different space within the room,” Torremorell says.

Only a few of the non-vaccinated pigs tested positive during the course of the study.

“What we saw, interestingly, is that there was some very limited transmission of the LAIV between vaccinated and non-vaccinated pigs,” she says. “There was some transmission, but the level of transmission was relatively low.”

She notes that transmission or lack of transmission could be associated with the presence of antibodies in the piglet against the live attenuated vaccine virus. More research is needed in this area, she says, to help producers better understand ways to manage when and how to vaccinate weaned pigs.

“Going into the study, I didn’t think there would be antibodies against the LAIV. But there were antibodies, so that could also explain why there wasn’t that much transmission of the LAIV. However, that’s something that would need further research,” Torremorell says.

What doors does this research open?

She believes this study serves as a base for other studies looking into testing live attenuated vaccines, understanding the conditions of how those vaccines are tested and what level of cross reactivity there might be against live attenuated vaccine viruses.

“Overall, this is important to understand how to better control influenza in the piglet population,” Torremorell says. “Also, it helps us understand reassortment of the influenza viruses between vaccine viruses and endemic viruses circulating at the farm.”

Part of her team’s research is directed at designing protocols to wean pigs that are influenza negative so that when they are vaccinated with products, like a live attenuated vaccine, they aren’t able to create reassortment viruses.

“Vaccines work better when there are no circulating viruses, because they are supposed to prevent from other infections. That’s part of our next steps for research,” she adds.

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