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When there's an outbreak of a vaccine-preventable disease, state health officials typically take certain steps to alert residents and issue public updates about the growing threat.

That's standard practice, public health and infectious disease experts told NPR and KFF Health News. The goal is to keep as many other vulnerable people as possible from getting sick and to remind the public about the benefits of vaccinations.

But in Louisiana this year, public health officials appeared not to have followed that playbook during the state's worst whooping cough outbreak in 35 years.

Whooping cough, also called pertussis, is a highly contagious vaccine-preventable disease that's particularly dangerous for the youngest infants. It can cause vomiting and trouble breathing, and serious infections can lead to pneumonia, seizures and, rarely, death.

Dr. Madison Flake, a pediatric resident in Baton Rouge, La., cared for a baby who was hospitalized during this year's outbreak. At less than 2 months old, he was sent to the intensive care unit.

"He would have these bouts of very dramatic coughing spells," Flake said. "He would stop breathing for several seconds to almost a minute."

Infants are not eligible for their first pertussis vaccine until they're 2 months old, but they can acquire immunity if their mother was immunized while pregnant.

By late January 2025, two babies had died in Louisiana.

But the Louisiana Department of Health waited two months to send out a social media post suggesting people talk to their doctors about getting vaccinated.