All those viruses brought in by undocumented illegal aliens? They have taken a toll. One of my friends who teaches English to them under a federal grant program in Chicago nearly died when she contracted a virus from them, and now must rely on steroids to have a life.
California politicians who refuse federal authority should be jailed or worse.
While I do think that some viral and bacterial infections come into the US via illegal aliens and also unvaccinated US citizens who travel abroad and come home and bring back diseases like Measles.
https://www.dailynews.com/2015/02/04/disneyland-measles-outbreak-dwarfed-by-2014s-in-ohios-amish-country/
But influenza is not one of them. Influenza has been around and has killed many millions long before illegal immigrants to the US started arriving.
http://www.influenzavirusnet.com/history-of-influenza.html
You could stop all illegals from coming into the country but would still have influenza outbreaks.