A recent study shows that a vaccine introduced in the year 2000 has had notable success against a common childhood affliction: ear infections.

Researchers at the Rochester General Hospital Research Institute followed 615 children over a decade to track how often they got ear infections after getting vaccinated. By age 3, 60 percent of the children had at least one ear infection, which was a significant drop from the 80 percent that had been reported in a similar study in 1989. Only 24 percent of the children had repeat infections, down from 40 percent.

The researchers attributed this drop to vaccines that protect against bacteria that can cause ear infections along with more serious ailments, including pneumonia and meningitis. The pneumococcal vaccine was introduced in 2000 and upgraded in 2010.

Most ear infections go away on their own, but they still lead to around 30 million doctor visits in the U.S. each year. Also, they are the most common reason why doctors prescribe antibiotics to children. This concerns some physicians, who worry that overprescribing antibiotics increases children’s resistance to antibiotics.

While the vaccine has lowered the number of ear infections, it has allowed other bacteria to move in, including one strain that is not included in the current vaccine. The researchers say these germs aren’t killed by amoxicillin, the antibiotic most prescribed for ear infections.

Lastly, vaccines alone won’t completely shield children from getting ear infections. The researchers cited other factors that medicine can’t control, such as family history and day care attendance.