California has one of the strictest requirements for childhood vaccinations in the U.S. after the state eliminated exemptions based on philosophical and religious grounds in 2015.
Yet the state has seen a rise of unvaccinated children over the past couple years due to physicians granting medical exemptions from immunization.
At least two children with medical exemptions contracted measles during an outbreak in the state last year, potentially exposing others to the highly contagious virus. That fuels fears that some clinicians are contributing to immunization coverage gaps by helping vaccine-hesitant parents bypass the state's vaccination requirements.
The published findings Thursday on a measles outbreak in Santa Clara County between March 4 and April 3, 2018. Out of the seven measles cases, two were children with medical exemptions despite having no underlying health conditions that would make them ineligible for the MMR vaccine, such as a severe allergy or a compromised immune system.
"This outbreak showed we shouldn't be lulled into a false sense of security that because of the law everyone is vaccinated," said Dr. George Han, deputy health officer at the Santa Clara County Public Health Department.
California experienced one of its worst measles outbreaks in 2014, when more than 125 cases were traced to Disneyland. Of the 110 cases involving California residents, 45% were unvaccinated, according to the . That led to a push for the law.
California is one of only three states—including West Virginia and Mississippi—to ban religious and personal-belief exemptions. Yet studies have shown that while immunization rates have gone up and personal exemptions decreased after the laws went into effect, medical exemptions rose.
Medical exemptions increased from 0.17% to 0.51% during the 2015-16 school year, according to a 2017 study published in .
The CDC report found that one patient, a 33-year-old male, was infected by his 7-year-old nephew. The child and his 4-year-old brother had identical, broad medical exemptions from all vaccines, and the physician who granted them was several hundred miles away from their home.
A of kindergarten immunizations for the 2017-18 school year found that the proportion of students who claimed a medical exemption increased over the prior school year from 0.5% to 0.7%. Rates of permanent medical exemptions to required immunization have increased 250% since the 2013-14 school year, from 0.2% that year to 0.7% in 2017-18. The state recorded an immunization rate of 95% for 2017-18 but had a 0.4% decrease in the number of students who were reported to have had all required vaccines compared to 2016-17.
The increased number of parents opting to not vaccinate their children from preventable diseases such as measles, mumps and chicken pox has been cited by public health officials as one of the causes for a spike in outbreaks. Between Jan. 1 and Feb. 28, a total of six measles outbreaks have occurred across 11 states, including California, resulting in more than 206 cases, according to the .
The largest single measles outbreak so far this year occurred in Clark County, Wash., where 68 cases of the virus have been confirmed as of Friday, according to the . Among those infected, 59 cases, or 86%, were reported to be unvaccinated.
"There's definitely a trend and the trend is in the wrong direction unfortunately," said Karen Hoffmann, president of the Association for Professionals in Infection Control and Epidemiology.
Nationwide, 91% of U.S. children between the ages of 19 and 35 months are vaccinated with the , according to the CDC. Among children entering kindergarten the rate is 94%.
But rates vary among communities, with vaccination rates in some areas having fallen well below the 93% to 95% coverage that is needed to maintain herd immunity.
While California's MMR immunization coverage rate meets the herd immunity minimum of 95%, places like Humboldt County fall well below the threshold. That county's vaccination rate for 2017-18 was 88% and 4.9% of children reported receiving a medical exemption.
During a House Energy and Commerce Committee hearing last week, Dr. Anthony Fauci, director of the NIH's National Institute of Allergy and Infectious Diseases, said misinformation about vaccine safety led to more parents opting not to vaccinate their children. He said healthcare providers can counter false claims when they talk with parents.
But the CDC report raises concerns that clinicians are playing a part in perpetuating vaccine myths by offering parents a way to get around immunization requirements.
"I think it's unfortunately because we have enjoyed the benefits of vaccination that this topic has become a victim of itself," said Dr. Gerald Winston Tripp II, chief medical officer for Centura Health system's St. Anthony Hospital in Lakewood, Colo.
The recent measles outbreaks have compelled lawmakers in several states to examine whether to set tougher school immunization requirements aimed at making it harder for parents to choose to opt out of vaccinating their children.
Some have suggested creating a more uniform standard for determining whether a child's health status makes them ineligible for receiving the MMR vaccine rather than our current system that relies on the individual physician.