California is facing its second-worst whooping cough epidemic in nearly 70 years. By September 15, 8,278 cases had been reported, in addition to three related deaths, according to a report by the California Department of Public Health (CDPH). The East Bay wasn’t spared: Alameda County accounted for 306 of those cases, and Contra Costa County, 282.

Now that the school year is well under way, local health officials are urging parents to immunize their children against pertussis—the scientific name for whooping cough—and other vaccine-preventable diseases like measles and mumps that showed a resurgence after decades of control.

This is a tall order in a region where some families still have limited access to healthcare, and more parents are filing Personal Belief Exemptions (PBEs), opting out of district vaccination requirements on religious or philosophical grounds.

Rachel O’Neal, a Berkeley mother of two, one a first grader in a Berkeley public school, has filed PBEs for her children. O’Neal said that she had formulated a mistrust of the western medical system early in her life, and had gone on to study homeopathy. She said she was concerned that some ingredients used in vaccines could cause harmful side effects, or trigger illnesses in her children. “I understand why people do it,” she said, “and I totally recognize I’m benefiting from herd immunity. I know that my personal belief is allowed to happen because other people are getting vaccinated.”

But, she said, “There’s so much information out there,” and went on to say that she didn’t want to make the decision out of fear either way. “Indecision has been my decision,” she said.

The percentage of California kindergartners whose parents have filed PBEs has doubled to 3.1 percent from 1.5 percent since the 2007-2008 school year, according to data from the CDPH. But many cases of kids missing their shots are unintentional, the result of not having time or access to adequate health care.

One mother of an Oakland public elementary school student taking her son for “catch-up” vaccinations at a Thursday clinic at the Family Justice Center in Oakland said that she worked full time, did not have health insurance, and that “scheduling and time” were her major obstacles in keeping her son’s vaccinations up to date.

But there is near-unanimous agreement among public health officials that vaccines are important and effective. “Most parents today have never seen diseases such as polio, diphtheria or measles,” said Gil Chavez, deputy director and state epidemiologist at the CDPH. “The low levels of these infections are a direct result of vaccines, so it is ironic that the very success of vaccines have led to some individuals thinking they’re not necessary.”

By California law, every child entering kindergarten, in both public and private schools, is required to be immunized against diphtheria, tetanus, pertussis, varicella (chicken pox), meningitis, measles, mumps, rubella, polio, and hepatitis B. Chavez says that vaccinating school kids is crucial to controlling these diseases. “Schools are highly susceptible to outbreaks of infectious diseases,” Chavez said, “because students can easily transmit illnesses to one another as a result of poor hand-washing, uncovered coughs and dense populations.” Once infected, he said, school kids can then further spread disease to more vulnerable members of their communities.

Pertussis is a bacterial respiratory infection. It can start off as a cough and runny nose lasting two weeks, but can escalate to a racking cough that empties the lungs, creating the disease’s signature “whooping” sound as the patient gasps for air. The DTaP (diphtheria, tetanus, pertussis) vaccine administered to infants cannot be given before the age of 6 weeks, making the disease especially dangerous, even lethal for newborns. Mothers are therefore advised in all pregnancies to get a Tdap booster (a variant of the DTaP for adolescents and adults), as antibodies are passed to children in utero.

The resurgence of pertussis in California began in 2010, the first major outbreak since 1947. While many factors likely contributed to the upswing, some health officials say that unvaccinated school children may have played a part in transmitting the disease to over 9,000 people that year, resulting in the deaths of 10 infants too young to be immunized.

A 2013 study by researchers at Johns Hopkins University examining the significance of Non-Medical Exemptions (NMEs), a category that includes PBEs, in connection to the 2010 California pertussis outbreak found that “geographic areas with high rates of NMEs are associated with high rates of pertussis.”

“Our findings suggest that communities with large numbers of intentionally unvaccinated or under-vaccinated persons can lead to pertussis outbreaks…putting those who are most susceptible to communicable diseases, such as young infants, at increased risk,” the study concluded.

Yet immunization does not guarantee 100 percent prevention of whooping cough. Due to “waning immunity” of the vaccine, children can contract pertussis even after being immunized. But it does slow transmission and reduce cases, officials say.

“Pertussis epidemics will still occur every 3-5 years,” said Chavez. But, he said, “ensuring that people are up to date with pertussis vaccine reduces the number of pertussis cases overall.”

“In the pre-vaccine era, the rate of pertussis was six times higher than it was during the 2010 epidemic year,” he said.

Reasons children go unvaccinated in the Bay Area are myriad: from distrust of pharmaceutical corporations and the government, to not having time to visit their healthcare providers.

“Some parents are suspicious of the MMR vaccine,” said Sarit Shtivelman, a pediatrician at Diablo Valley Pediatrics with offices in Concord, Antioch and Brentwood, referring to the measles, mumps and rubella vaccine. She said that concerned parents mostly cite a 1998 study by Andrew Wakefield that was retracted by the journal Lancet, linking the MMR vaccine to autism. “His study was retracted, he was removed from the Medical Register and couldn’t practice medicine in the UK anymore,” said Shtivelman.

But, she said, most kids go unimmunized for a much more common reason: time constraints. “We see a lot of discontinuity of care; missing appointments, transferring clinics,” said Shtivelman. She said that newborns need a regimen of four DTaP shots in their first 15 months of life, and many families can’t keep up with appointments, or don’t have the medical experience or forethought to request charts to bring to other clinics.

Similarly, Professor Arthur Reingold, the head of Epidemiology at the UC Berkeley School of Public Health, said that often members of poorer communities will not have time to vaccinate newborns, and have to undergo “catch-up” immunization schedules. Under-immunization, or “vaccine hesitancy,” he said, tends to be prevalent in parents of older children in more affluent communities.

“In California, both NME and pertussis clusters were associated with factors characteristic of high socioeconomic status,” the Johns Hopkins study found. State health department data also reveals PBE rates in California to be 2.96 percent higher in private schools than public. In some schools, such as the East Bay Waldorf School in El Sobrante, the number of PBEs is as high as 50 percent.

“There’s a lot of mischievous, incorrect information on the web,” said Reingold, pointing to anti-vaccine firebrands like Jenny McCarthy and Michelle Bachmann who, at one point, linked vaccines to autism and a dystopian, state mandated infringement on civil rights, respectively. Reingold said that some “vaccine-hesitant” parents believe in allowing their kids to fall ill and develop antibodies “naturally.”

In the game of immunization, there’s often power in numbers. It’s what’s called “herd immunity,” the idea being that the more people immunized in a given community, the less likely it is that unimmunized individuals will encounter pathogens. The herd model is effective against a disease like measles, since it has an extremely effective vaccine—two doses can provide near-lifetime immunity. If kids are immune, it’s unlikely they’ll contract and spread the disease to others.

However, said Reingold, herd immunity is much less relevant to pertussis, whose acellular vaccine—compared to the whole cellular vaccine discontinued in the 90’s due to more severe fever and “fussier babies”—is not as effective and provides less long-term immunity. In short: Infected kids can easily transmit the illness to others, even if they’ve been immunized.

The Johns Hopkins study estimates that greater than 95 percent of the population must be immune to prevent outbreaks and suppress sustained transmission of pertussis and measles. “Herd immunity must be maintained to reduce the risk of disease for those too young to be vaccinated or unable to receive vaccines,” the study concludes.

But getting the majority of families to comply is a more difficult challenge. Last year, CDPH data showed that as few as 20 percent of students were up-to-date with vaccinations in some Oakland schools. However several nurses, including Pauline Stango at Encompass Elementary, insisted that these numbers were not accurate. She said that many schools, like hers, were short-staffed, and did not have a full-time secretary to enter student medical data.

Troy Flint, spokesperson for the Oakland Unified School District (OUSD), also said that some of the district’s low immunization rates were due mostly to misinformation and poor health care access for students. But, he said, this year, OUSD is partnering with Alameda County Public Health Services to administer on-site flu vaccinations and health clinics. He said they hoped to reach flu immunization levels of 70 percent by the end of the school year.

Gil Chavez of the CDPH noted that the Vaccines for Children Program provides vaccines at no cost to children through a network of over 4,000 enrolled providers.

Families can find out where children can get free vaccinations by visiting www.shotsforschool.org, or consulting the Alameda County Public Health Department.