If you've ever had to talk a college student into getting a flu shot, researchers at the University of Minnesota just made your case.

Vaccinated students are:

46 percent less likely to miss a class.

40 percent less likely to botch an assignment.

47 percent less likely to have a bad test.

47 percent less likely to have to go to the doctor.

In short, the vaccine prevents an illness that can knock college students off their feet for up to a week at a time. Multiplied over four years and 18 million college students nationally, that's a lot of lost learning.

"We're excited to show bad disease, good vaccine, yet again," said Dr. Kristin Nichol, a professor at the University of Minnesota and an infectious disease expert at the Minneapolis Veterans Affairs Medical Center.

She and other researchers surveyed nearly 20,000 students at the university and St. Olaf College over four years to measure the cumulative effect of the flu and the flu vaccine on their lives.

On average, the 30 percent who were vaccinated reported better health and better performance at school and work compared with those who were not vaccinated.

The study was published Monday in the Archives of Pediatric and Adolescent Medicine. Researchers have long known that the vaccine can prevent flu, but this study quantifies in multiple ways its beneficial effects.

Overall, one-fourth of the students who were not vaccinated said they had an influenza-like illness, defined as an upper respiratory infection that included coughing and fever. That compares to one-fifth of students who were vaccinated.

For the unvaccinated, those infections resulted in more missed classes (11 percent vs. 8 percent); more bad tests (6 percent vs. 4 percent); more uncompleted homework (9 percent vs. 6 percent), and more badly executed assignments (11 vs. 8 percent.)

"We know that if the number of days they are ill goes up, their GPA goes down," said David Golden, marketing director for the Boynton Health Service at the university. That's why health officials there are ramping up the "get a flu shot" message. It seems to be working. Now, about 40 percent of university students get vaccinated, he said, up from 30 percent in the winter of 2005-06, the last year of the study.

Infectious diseases can be particularly severe on campuses, where students live and study in close quarters.

In an earlier survey of 3,250 students published in 2005, Nichol measured the impact of all those shared illnesses. She found that upper respiratory infections, including colds and flu-like illnesses, resulted in 6,023 bed days, 4,263 missed school days and 45,219 days of illness. Nearly a third who reported being sick did badly on a test, and 46 percent did poorly on a class assignment.

"Some of this is preventable," she said. "And who wouldn't want to prevent it?"

Josephine Marcotty • 612-673-7394