DEAR MAYO CLINIC: Cases of COVID-19 are once again surging in parts of the U.S., and I’m hearing about different strains, such as the BA.5 and BA2.75 omicron subvariants. What do I need to do to keep my family safe, especially as I prepare to send my kids back to school? My children and I have received two doses of a COVID-19 vaccine and a booster vaccination.