Trade groups representing Minnesota's doctors and other health professionals appealed Thursday to parents to get their children up to date on vaccinations before the start of the school year. A major reason for their concern: Minnesota ranked 44th among states in 2011 for the percent of children who are up to date with their shots.

"There's a lot of measures that Minnesota does great on, but childhood immunization is not one of them," said Dr. Peter Dehnel, a pediatrician who spoke on behalf of the Minnesota Medical Association. "What it means is we'll have periodic outbreaks of things like measles and certainly pertussis. And many of these diseases are preventable … Children are getting sick who don't need to get sick."

Minnesota's poor ranking is a bit deceptive; the state is closer to national averages in the percent of children who receive timely vaccinations against diphtheria-pertussis-tetanus, polio, measles-mumps-rubella, hepatitis B and varicella. The state's problem remains the low rate of children receiving Hib vaccine. Only 69.5 percent of Minnesota children received three doses of Hib vaccine as recommended before they turned three, according to federal data for 2009. The national rate was 85 percent.

(Hib is short for Haemophilus influenza type B, and is a leading cause of meningitis in children. Minnesota had a Hib flare-up in 2009, when one child died from an infection and four others suffered serious complications.)

The state was hit particularly hard by a Hib vaccine shortage that emerged in 2008 after manufacturer Merck had to shut down a vaccine plant. Merck at the time was responsible for half the nation's Hib vaccine supply. Prior to the shortage, Minnesota had one of the nation's best Hib and overall vaccination rates. After the shortage, many children either received no doses or only one or two doses -- meaning that they weren't considered fully immunized.

Despite the extenuating circumstances of Minnesota's poor national ranking, advocates believe there are other reasons to be concerned. Minnesota has a relatively higher rate of parents who opt their children out of vaccination requirements because the state allows them to object for religious reasons OR for other concerns. It is also seeing a record increase in childhood cases of pertussis (or whooping cough) this year.

Minnesota also was highlighted last week by the U.S. Centers for Disease Control and Prevention for a case that showed the value of so-called "herd immunity." A three-year-old Minnesota girl with a weakened immune system couldn't receive the varicella vaccine due to potential health risks. Her parents also declined to immunize a younger daughter because of personal beliefs. The younger girl suffered chicken pox, and then passed the infection to her older sister. The older sister (who suffered from juvenile rheumatoid arthritis) was hospitalized for a week due to the severe infection, which produced more than 500 skin lesions and blisters in her mouth and throat.