Health officials are concerned about the worst whooping cough epidemic recorded in California seven decades.

It's the worst epidemic of whooping cough since a new vaccine was introduced in the 1990s that research has concluded doesn't last as long as the old one.

The new vaccine is "gentler" and weaker, with effects wearing off more quickly and more cases of the disease resulting. The vaccine may keep people from getting sick with whooping cough, but it doesn't keep them from spreading the disease, according to one study.

NBC News notes health officials have acknowledged the situation is bad, and likely to get worse, with one baby succumbing to the disease and 9,935 people becoming sick. Those are cases reported to the California Department of Public Health from Jan. 1 to Nov. 26.

There are 26 cases of the disease per 100,000 people, but 175 cases per 100,000 people for infants under the age of 1, according to USNews.com.

The disease is cyclical, peaking every three to five years as immunity from the vaccine or the disease wanes. California's last epidemic was in 2010, the Associated Press reports.

And this "new normal" of higher infection rates is likely to continue until new vaccines come out, according to a California Department of Health report.

The vaccine is called Tdap, and women are encouraged to get vaccinated in the last weeks of pregnancy to avoid their babies falling ill.