We study how the flu virus spreads between people. While we strongly encourage everyone to get the flu vaccine, the findings from our study on the stability of flu viruses in the air can provide useful information for parents, teachers and health care officials to limit the spread of flu in the community.

In the early 20th century, the leading cause of death was infectious disease. Epidemics erupted with little warning, seemingly out of the blue. When the “Great Influenza” struck in 1918, it killed thousands of people a week in American cities and spread like wildfire around the globe. My great aunt, still a teenager, and living in the San Francisco area, was one of its estimated 50 to 100 million victims worldwide.

During my second year of graduate school, I moved in with my sister’s family to save money. “You must get the flu shot if you are going to live here,” my sister declared. Both of my nieces were under the age of 5, putting them at a high risk of flu complications; therefore, it was critical that I do my part in, first, getting vaccinated to minimize my risk of getting the flu, and second, not passing the flu to a vulnerable population. A key part of this was, and still is, washing my hands regularly.

The current 2017-18 flu season is a bad one. Hospitalization rates are now higher than in recent years at the same point, and infection rates are still rising. The best line of defense is the seasonal influenza vaccine. But H3N2 viruses, like the one that’s infecting many people this year, are particularly hard to defend against, and this year’s shot isn’t very protective against H3N2.

Every year, from 5 to 20 percent of the people in the United States will become infected with influenza virus. An average of 200,000 of these people will require hospitalization and up to 50,000 will die.