DENVER (CBS4) – Colorado’s whooping cough epidemic is getting worse as health officials confirmed Monday there are now more than 1,000 cases in the state.

This is the worst year for whooping cough in seven years. Health officials say whooping cough tends to peak every three to five years.

In 1997 the vaccine was changed. There are concerns it may not offer the long-lasting protection.

Dr. Kathy Beauchamp is the chief of neurosurgery at Denver Health Medical Center. At home she’s the mother of seven.

“Julie and Jack are the twins — Joey, Jeffrey, Janie, James and Jay,” she said.

They’ve all had the occasional cold, but this year six of the seven have gotten very sick.

“I thought it was just a really bad cough,” Beauchamp said.

It started in July with Joey and then spread to the twins and Jeffrey. The babies were the worst.

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“They would cough for at least a couple of minutes and then it always ended with vomiting,” Beauchamp said.

It turns out all but 6-year-old Janie had pertussis, or whooping cough.

“They were all vaccinated on time, every one of them,” Beauchamp said.

“What we are learning is that the vaccine we’ve used since the mid 1990s actually only lasts about, give or take, five years,” Dr. Simon Hambidge with Denver Health said.

Joey, who brought the disease home, was five years out from his shot. Hambidge says the other children were vulnerable.

“Once you’re exposed at a really high level, even though you’re vaccinated, you have a higher chance of coming down with it,” Hambidge said.

He believes Janie was protected because she’d just had her kindergarten booster.

“We now recommend an additional booster starting at 11 years of age,” Hambidge said.

Hambidge says being up to date on immunizations is the best protection from pertussis. It’s called the 100-day cough.

Beauchamp looks forward to the day her family is finally cough free. Two of her children are still coughing.

Anyone can get whooping cough but it’s most dangerous in infants and young children. It’s recommended that all adults get the Tdap booster.