The infection rates of whooping cough are three times to five times higher in Elk Grove, a large suburb in Sacramento, California, despite most of the residents choosing to have their children vaccinated.

State data reveals that only 80 of Elk Grove's 4,500 kindergartners did not receive vaccinations last year. The high rate of infection despite the high rate of immunization raises concerns that the current vaccine for whooping cough may have lost its potency.

The whooping cough vaccine seems to be wearing off only after a few years, causing people to contract the disease even while they thought they are protected.

"This newer version of the vaccine probably has a shorter period of protection. I think that is a scientifically proven point," said UC Davis Children's Hospital chief of pediatric infectious diseases Dean Blumberg.

Whooping cough, also known as pertussis, leads to fatigue, vomiting and a distinct "whoop" sound that patients make as they attempt to catch a breath following a coughing fit. The disease is dangerous to babies, with four infants dying from whooping cough last year in California.

It was only in the 1940s when a vaccine for whooping cough was developed and administered in California. This version of the vaccine was very effective, decreasing the cases of whooping cough in the state from thousands of patients per year to only dozens.

However, the vaccine led to extreme side effects in a small percentage of children, leading to high fevers and seizures, causing parents to choose to refuse to have their children vaccinated.

A new kind of whooping cough vaccine was then introduced in the 1990s that mitigated the side effects. However, the price is that the protection provided by the vaccine steadily declines over a few years, which leaves both adults and children vulnerable until they receive a booster shot.

California requires children attending its schools to receive vaccinations against several diseases, including whooping cough and measles, before they enter kindergarten. However, thousands of families apply for "personal belief" exemptions every year, leaving their children without vaccines.

Similar to the outbreak of measles in California, the parents of the children that are unvaccinated have received most of the blame from the public for the outbreak of pertussis. However, the connection between the unvaccinated and the contraction of whooping cough is not as strong compared to children that have contracted measles in the current outbreak.

A record number of 11,000 people living in California contracted pertussis last year. Around 4,500 of these people resided in counties where less than 2 percent of kindergarten students did not receive vaccines last year.

"It's not correct to only pin (the pertussis outbreak) on the people who are unvaccinated," said University of California, San Diego pediatrics professor and U.S. Centers for Disease Control and Prevention immunization practices committee member Mark Sawyer. "The effectiveness of the vaccine is a huge part of this. People who are immunized do still get pertussis."

However, Sawyer added that it is still important for people to receive the vaccine.

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