We’re getting into the cold months when more people will be gathering indoors and respiratory illnesses like COVID-19 thrive. Requiring some proof of immunity is becoming more standard and widely accepted, and it remains a generally good rule. And the new boosters, now finally available to all adults, will help with this immunity. But immunity alone has proven insufficient to protect a gathering, particularly in the new environment of more aggressive and contagious variants like delta and omicron. Breakthrough infections — those in people who are already immunized — are on the rise. A stark demonstration of this is the...