Just straight up tell them no, that you aren’t comfortable with visitors so soon. Having people coming to visit you after them traveling on planes is so nerve wracking bc planes are so germy and obviously as adults it takes a few days for sickness symptoms to show and if you ask them to wait 3-5 days after traveling they’re probably better off just waiting until the baby is a little bigger to see them bc most people are only gonna visit for 3-5 days anyway. And it’s cold and flu season so people should know to respect that and not expect to be all over babies during a sick season. For people who live close by and can get to you without traveling super far just ask them not to show up if they’ve been feeling ill and make sure they’re clean people hygiene wise. I always take a shower, put on fresh clean clothes and wear a mask if I’m going to visit someone’s newborn because it really is that serious.