The number of whooping cough cases in California has hit a record-high this year, and a new analysis has found that infants have been the most badly hit by the epidemic, prompting calls for more aggressive efforts to vaccinate pregnant women to provide protection for their babies.

Between Jan. 1 and Nov. 26 this year, there have been 9,935 individuals diagnosed with whooping cough in California, which is equivalent to 26 cases per 100,000 people, the U.S. Centers for Disease Control and Prevention (CDC) revealed in its Dec. 5 issue of the Morbidity and Mortality Weekly Report.

The incidence rate is the highest in nearly 70 years, surpassing California's 2010 epidemic, which had 9,159 reported cases and 10 deaths.

Whooping cough, also known as pertussis, is highly infectious and can spread through coughing and sneezing. While vaccination provides protection against this respiratory illness, health officials are concerned about the waning immunity of those who have been vaccinated.

In the 1990s, a new vaccine was used because parents were getting upset over the side effects caused by the older vaccine. The vaccine, which was used before, caused seizures and was more painful. The new vaccine is gentler and has fewer reactions, but its effects do not last long.

Health experts from the CDC said that infants below one year old were the most affected by the outbreak, particularly those from Hispanic groups.

There was also a high incidence of the disease among teenagers between 14 and 16 years old, most of whom received tetanus, diphtheria, and acellular pertussis (Tdap) vaccine before. The trend indicates that their illnesses were caused by the waning protection provided by the vaccine.

"Acellular pertussis vaccines are less reactogenic than whole-cell vaccines, but the immunity conferred by them wanes more quickly," the CDC report reads. "Most of the cases among adolescents aged 14-16 years were among those who had previously received Tdap ≥3 years earlier, suggesting that their illness was the result of waning immunity."

Since the respiratory illness is contagious and potentially fatal, it is crucial to identify the symptoms of the disease to prevent it from spreading and to be able to get the necessary treatment as early as possible. Infants often need to be hospitalized because the disease can be very dangerous for children their age.

Pertussis often starts with cold-like symptoms and sometimes with mild cough or fever. After about two weeks, the coughing fits become more severe. The illness is characterized by vomiting and exhaustion, and the coughing is often followed by a high-pitched "whoop." Coughing in infants may be minimal, but they tend to have apnea or pauses in their breathing pattern.

"Pertussis can cause violent and rapid coughing, over and over, until the air is gone from the lungs and you are forced to inhale with a loud 'whooping' sound," the CDC said. "This extreme coughing can cause you to throw up and be very tired."

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