xyzcf: please share if you think its useful. If you don't mind tack on the "herd immunity" addendum as I think its valuable information.
Ready: I'll chime in. You are very correct, your parents are much better off staying put, having someone with them and not going into California right now. Is there ANY urgent and real reasons they should do this? If not it is not wise.
Thunder: I am not being anti-US, but the truth is there is a lot more of that going on than you may believe. First look at governors of ENTIRE states who said it was a hoax, go out to Bob Evans and eat with your families, and Florida is the poster child of this kind of thing. Florida MAY already have 100s of thousands of infected people and they JUST instituted movement restrictions. Its way too late, the geometric wave will crush their capacity. And Florida has a lot of older vulnerable population. And even where my home is in the US (very wealthy, very blue) you hear of group of people on golf courses proudly refusing to socially distance because its all a "liberal plot." This is not a political point I am making, I am saying there is a very significant portion of people in the US that are no longer able to see anything outside of a political lens, even if its about health of others. Yes I see some "nutters" here in London, but trust me, they are the very rare exception, political beliefs is NOT shaping if people are following guidelines or taking this seriously. Polls show majority of one party does not believe this is serious and they think it is being played up for political reasons.
US not only acted too late, its still not acting as per best knowledge and practice. And there is minimal coordinated Federal effort. Are you aware that states are forced to compete with each other and bid up the cost of ventilators because the Federal government refuses to be the central help? By contrast all of EU has joined together and is bulk purchase and providing PPE and ventilators as a group. And people are raising their eyebrows that UK has not joined them yet because of "Brexit." Some states are taking the initiative, some are not. And not all states have the resources of California and Washington state to deal with this. It would be like asking individual village doctors to handle the situation with central help.
The situations are not equivalent. Other from Canada will chime in about what its like up there.