Two days ago 1.3 million Americans traveled through US airport security checkpoints, according to the Transportation Security Administration, the highest single day tally of travelers since the COVID-19 pandemic began in the country last March.The impact of Christmas and New Year's celebrations and travel has yet to be fully seen, but many states are preparing for a surge of infections while trying to simultaneously obtain and distribute the first doses of two approved COVID-19 vaccines.In hard-hit areas, including Southern California, the Emergency Medical Services Agency is telling paramedics to conserve oxygen because of a shortage and to not bring patients with little chance of survival into hospitals.