Doctors have a message for vaccine-weary Americans: Don’t skip your flu shot this fall. And for the first time, seniors are urged to get a special extra-strength kind. There’s no way to predict how bad this flu season will be. Australia just emerged from a nasty one. In the U.S., annual flu vaccinations are recommended starting with 6-month-olds. Because seniors don’t respond as well, the U.S. now recommends they get one of three types made with higher doses or an immune-boosting ingredient. Meanwhile, the companies that make the two most widely used COVID-19 vaccines now are testing flu shots made with the same technology.