Rich Pedroncelli, AP
An empty bottle of Tetanus, Diphthera and Pertussis, (whooping cough) vaccine is seen at Inderkum High School in Sacramento. Calif.

Parents of children in private schools in California are more than twice as likely than public school parents to opt their children out of immunizations, according to a recent Associated Press analysis.

"Public health officials believe that an immunization rate of at least 90 percent in all communities, including schools, is critical to minimizing the potential for a disease outbreak," reported the Associated Press. "About 15 percent of the 1,650 private schools surveyed by the state failed to reach that threshold, compared with 5 percent of public schools."

The resurgence of whooping cough has made headlines lately, but even after whooping cough reached epidemic levels in California in 2010, opt-out rates have continued to climb in private schools, reported the Associated Press.

"As kids get older, they are more at risk for catching certain diseases, like meningococcal meningitis, so they need the protection that vaccines provide," according to the Center for Disease Control and Prevention. " "For other diseases, like whooping cough, the protection from vaccine doses received in childhood wears off over time. That's why 11- and 12-year-olds are also recommended to get the booster shot called Tdap."

This is not just a private school issue. In Connecticut and other states, it is possible to get vaccination exceptions for public school students for various reasons, according to a Westport News article.

"The Connecticut Department of Public Health reports that last year 1,056 children entering kindergarten and seventh grade received exemptions, a 127 percent increase from 2003, when the state recorded only 465 such exemptions," reported Westport News.

There are many reasons some parents are hesitant or downright refuse to get their children vaccinated. Religious, medical and even "philosophic" reasons are all valid reasons for vaccination exemptions in many states, and some parents still believe that vaccinations can lead to autism, according to reports.

Vaccination numbers are still relatively high in states like Connecticut, but the rising cases of exemption and opt-outs do have doctors concerned, according to Westport News.

"If you have more and more kids not getting vaccinated, then you have more and more of a pool for illness to take hold," said Dr. Robert Chessin, a pediatrician at Pediatric Healthcare Associates in Bridgeport and Shelton, in Westport News.

This year could be one of the most deadly in quite some time for sufferers of whooping cough, and the CDC reports that last year the number of reported cases of measles was higher than usual.

"Politicians and public health experts across the nation are focusing more attention on childhood immunizations, driven by a re-emergence of diseases like whooping cough," reported the Associated Press. "The U.S. is in the midst of what could be its worst year for that disease in more than five decades, with nearly 25,000 cases and 13 deaths."