For many South Florida parents, the back- to-school rush means buying new backpacks, notebooks and pencils.

And don’t forget the immunizations.

Documentation for required immunizations is mandatory for all students entering, attending or transferring into a Florida school in grades pre-kindergarten through 12, unless they are granted an exemption for medical, religious or other reasons, according to the Florida Department of Health.

Though kids hate shots, vaccines are the best defense they have against serious, preventable, and sometimes deadly contagious diseases, according to the U.S. Department of Health and Human Services.

“Vaccines are extremely important,” said Dr. Jose Rosa-Olivares, medical director for Miami Children’s Hospital’s Pediatric Care Center. “There are some diseases that produce significant deaths in children that can be prevented with vaccines.”

Nowadays, vaccines cover about 30 different diseases. Some of the vaccines are grouped under one vaccine; other vaccines are for individual diseases, he said.

In simple terms, vaccines help the body’s immune system prepare for future attacks. Vaccines consist of killed or modified microbes, parts of microbes, or microbial DNA that trick the body into thinking an infection has occurred. A vaccinated person’s immune system then attacks the harmless vaccine and prepares for invasions against the kind of microbe the vaccine contained, government health authorities say.

In this way, the person becomes immunized against the microbe: if reexposure to the infectious microbe occurs, the immune system will quickly recognize how to stop the infection.

Vaccines also work because of what is called “community immunity” or “herd immunity.”

When a majority of a community is immunized against a contagious disease, most members of the community are protected against that disease because there is little opportunity for an outbreak, health authorities say. Even those who are not eligible for certain vaccines — such as infants, pregnant women, or immunocompromised individuals — get some protection because the spread of contagious disease is contained.

“One of the ways vaccines work is having the majority of the population vaccinated,” Rosa-Olivares said. “And that minimizes the possibility of that disease.”

In recent years, a backlash has arisen against vaccines over concerns about autism.

One ingredient studied was thimerosal, previously used as a preservative in many recommended childhood vaccines. Thimerosal was removed or reduced to trace amounts in all childhood vaccines in 2001, except for one type of influenza vaccine, and thimerosal-free alternatives are available for influenza vaccines, according to the Centers for Disease Control and Prevention.

The Institute of Medicine conducted a scientific review, and the CDC said it supports the Institute of Medicine’s conclusion that there is no relationship between vaccines containing thimerosal and autism rates in children.

Pediatricians say that in August their offices tend to be full of kids needing check-ups and shots.

That’s particularly true for children starting public school for the first time, changing schools or entering the seventh grade. Private schools have their own policies, but tend to follow the same rules.