for chickenpox and for mmr, measles, mumps, and rubella. >> think about it wrash. >> reporter: marin county has seen a steady rise in the number of parents choosing to delay or skip vaccines altogether. in california by law children must be immunized against nine diseases, including polio, chickenpox, and measles before entering kindergarten, but parents can get around the law by signing a personal belief exemption. since 2004 the number of such exemptions in marin county has doubled to nearly 8%. the highest opt out rate in the bay area, and one of the highest in the state. >> there's the outbreak this year. >> whooping cough is on the rise this year. this trend alarms health officials like dr. matt willis and sharon forkel. they see a cocorrelation in the rise between personal belief exemptions and a dangerous dip, a kind of fire break which guards a community against the rapid spread of contagious diseases. >> we have many schools many marin county where the vaccination rates are below the level need for imunit. we've had outbreaks of veracella and outbreaks of protussis. a measle

it's turned out not to be the th case, but that started the whole trend and then you have the mmr and autism craze which was wa fueled by a discrediteddited physician who actually falsifiee scientific research and createdn a lot of problems for us. yes, we have a lot of pockets po around the country and in this study what it showed is those is pockets are in areas where wh parents choose not to vaccinatea their children where there's ane actual increase in disease. this situation with whooping cough. >> when parents choose not to having sin 8 vaccinate their ch. are they putting the child at risk for getting the disease or getting an infection from other children.childr >> certainly. all of these diseases are still prevalent around the world. wo whooping cough may infect 30 million people.eople. will kill upwards of 30,000 of people n that outbreak in 201010 in california there were 9100 cases reported and there's manyy that weren't reported. rert those who have been vaccinated may get a mild case. nonethelesser nonetheless, ten infants died in that outbreak. this is preventable by vi