Joanna Kempner, a sociology professor at Rutgers University, has been cautious all year and postponed a trip to see family and friends on the West Coast. After she and her adult family members were vaccinated and the number of cases plummeted, the time finally seemed right. So she, her husband, and their two children – too young to be vaccinated, at age 7 and 11 – flew to San Francisco. They went on a hike with friends who were as careful as they were. Less than a day later, her friend’s child tested positive for coronavirus and her daughter began to feel sick the next day. Then the whole family began to self-quarantine at a vacation home on Lake Tahoe, awaiting their test results, wearing masks and staying away from Kempner’s parents, who are in the house with them. So much for that. (The family then tested negative.)