(St. Paul, MN) -- The Minnesota Department of Health is encouraging adolescents and adults to get vaccinated for whooping cough or pertussis. The Health Department's Kris Ehresmann says they're seeing increased cases in elementary school age, adolescents and adults because their early childhood protection is wearing off sooner. She says the T-dap vaccination is safe and effective. So far this year there have been nearly 4,200 cases of pertussis reported in Minnesota. That's the highest total since the 1940s, in the years before vaccines were introduced.