HOUSTON-- Whooping cough has made a comeback, and right now California is in the midst of its worst outbreak in half a century with 3,600 cases and eight deaths.

Last year, Texas had 3,358 cases of the pertussis disease, which is also the most in50 years. Three deaths were reported.

Pertussis itself is a very bad bug, it is highly contagious, said UT Health Pediatrician Jason Sanders.

Doctors say the increase is due partly because the series of pertussis vaccinations you get as a child does not provide lifetime immunity. The vaccine wears off by about age 12.

That's what happened to the Throgmorton family.

In 2003, Haleigh Throgmorton came into the world a little ahead of schedule, so her father delivered her at home near Amarillo. Five-and-a-half weeks later Haleigh died from pertussis.

It was a shock, I mean we were floored that that's what it was, because it was something you never thought of being around anymore, said Jerri Lynn Throgmorton, the baby s mother.

Rodney Throgmorton, who hadn't been immunized since childhood, got whooping cough at age 34 and then unknowingly passed it on to his newborn.

By the time she passed away I had had the disease for a month, and coughing for a month, he said.

The disease is uncomfortable for adults, but can be deadly for infants under 6 months old, who haven't been fully immunized.

That's why in 2005, the U.S. Food and Drug Administration approved a whooping cough booster for everyone over age 11.

But there is another side to this story that is far more controversial.

Some doctors wonder if the actions of some parents are partly to blame for the rise of the disease. A growing number of them have decided not to vaccinate their children.

Rebecca Rex is among those parents.

I'm fully aware of the risk we've taken and the consequences of those risks if they don't go well, she said.

Her two sons, ages 17 and 11, have never been vaccinated, and she said they have never gotten whooping cough.

Rex is the co-founder of Parents Requesting Open Vaccine Education, or PROVE. She says there is evidence that vaccines can have dangerous side effects.

I'm not telling a parent to vaccinate or not, I am telling a parent to go out and do as much research as they can -- of information that is not hysterical, Rex said.

11 News checked with the Centers For Disease Control and found they have what's called the Adverse Vaccine Reporting System. We found reports where people said that within minutes or hours of getting the pertussis vaccine, they suffered from either abdominal pain, nausea, seizures or rashes. And in rare cases, some children died.

But doctors and CDC officials 11 News talked to said there is no evidence that suggests the vaccine is to blame.

It has been seen to happen after immunization, but there has been no correlation that it is related to that immunization, said Sanders.

So 11 News looked at the numbers to get a better perspective. In 2000, the CDC said, in the entire country, it received only 2,876 reports of adverse reactions to the pertussis vaccine. By 2009, the number dropped to 2,104.

Compare that to the millions of children who get the vaccine every year.

Rex and the government agree on one thing: there is under-reporting, because it is voluntary. So what should a parent do?

Rex encourages parents to check research papers and the CDC for information on all vaccines.

If you learn as much as you can about those two things then, generally, regardless of what you choose, it will be the right choice for your family, she said.