Reported cases of whooping cough have been on the rise in recent years and cases in Southern California have already been recorded at rates far higher than usual this year. Health officials say that these increases are likely due to decreased vaccination rates or reduced effectiveness of the current vaccine available.

In Long Beach, a city in Southern California, reported cases of whooping cough have shot up to 43 since January alone, as opposed to 15 cases for the entire year of 2013 and four for all of 2012. It is a surge in occurrence that is unprecedented, according to Michael Kushner, a Long Beach health official, who says that rates so high this early in the year have never been seen before.

It is believed that part of the reason that reported cases of whooping cough are on the rise stem from a reduction in the number of vaccines being administered. When vaccination rates drop, it compromises herd immunity, which protects people from contracting illnesses and helps to shield those who cannot receive the vaccines from exposure. In this case, bacteria transmitted through coughing and sneezing creates an infection that mimics a cold but with a persistent cough that remains for weeks. This infection can be quite dangerous for infants, who are especially vulnerable as they are too young to be vaccinated and rely on herd immunity for protection.

Another potential reason experts cite for the rise in cases is the modification done to the vaccine to help reduce the side effects, which previously included seizures. It is thought that altering the vaccine lessened its effectiveness. Instances of whooping cough have been on the rise since the vaccine was altered in the 1990’s and the Central for Disease Control is currently researching whether or not changes to combat undesirable side effects reduced the potency of the vaccine as it is currently being administered.