Barring Nonmedical Exemptions Increases Vaccination Rates, Study Finds

The first rigorously controlled study of a 2016 California law that aimed to increase childhood vaccination rates by eliminating nonmedical exemptions has found the law worked as intended, although the researchers noted a small increase in the number of medical exemptions.

The study provides definitive evidence on the success of the California law, as policymakers across the United States and around the world debate similarly strict vaccine requirements.

“Vaccine hesitancy and the recent decline in vaccination rates is an increasing threat to public health and our patients,” said Nathan C. Lo, MD, PhD, a medical resident at UC San Francisco and senior author of the study, published Monday, Dec. 23, 2019, in PLOS Medicine. “Our study shows that government policy has a role to address this, and that eliminating nonmedical exemptions is an effective way of increasing vaccination coverage.”

The researchers estimated how many California children would have received a key vaccine – measles, mumps and rubella, or MMR – if the law had not gone into effect, and compared that to how many children actually were vaccinated following the law’s enactment. The comparison group was created synthetically with data from 44 other states, so that it resembled California’s demographics and trends.

The researchers did something similar at the county level, comparing overall vaccine coverage in California counties to vaccine coverage in similar counties from 16 other states. The state data covered the years 2011 to 2017 and the county data covered 2010 to 2017.

“The big strength of our study over previous analyses is that we designed a quasi-experimental study with control groups, to adjust for ongoing trends in vaccination,” said Sindiso Nyathi, a PhD candidate in the Department of Epidemiology and Population Health at Stanford University School of Medicine, who was one of the first authors on the new paper. “This makes our results more reliable.”

Both analyses showed that vaccination rates went up following the law’s enactment. MMR coverage across the state increased 3.3 percent, compared to the “synthetic” state control; nonmedical exemptions decreased by 2.4 percent; and medical exemptions increased 0.4 percent.

In the county-level analysis, overall vaccination coverage went up on average 4.3 percent, nonmedical exemptions went down 3.9 percent and medical exemptions went up 2.4 percent. The averages masked much larger changes in vaccination coverage in some counties, which ranged from a 6 percent decrease to a 26 percent increase, with the largest increases happening in counties that had the lowest vaccine coverage before the law took effect.

“We did see an increase in medical exemptions, but in absolute terms the numbers remain small – 1 to 2 percent, driven largely by a few counties – and we can expect them to remain of similar magnitude in the near term,” Lo said. “Overall vaccine coverage increased by 10 to 20 percent in the high-risk counties, far more than the increase in medical exemptions.”

These changes were enough to bring the vaccination rate to 95 percent in almost all California counties, which is high enough coverage to create so-called herd immunity, which can prevent disease from spreading among vulnerable groups, like newborns and older children who cannot receive vaccinations for various medical reasons.

“The implication of our study is the law brought about protection through herd immunity,” said Hannah Karpel, a student at New York University School of Medicine, and a first author of the paper. “Even small average increases can have a big effect.”

Authors: Sindiso Nyathi, Kristin Sainani, Yvonne Maldonado and Eran Bendavid, Stanford University School of Medicine; Hannah Karpel, New York University School of Medicine; Peter Hotez, Baylor College of Medicine; and Nathan Lo, UCSF.

Funding: No funding was received for this study.

Disclosures: Lo receives funding from the World Health Organization for work outside the current study.


The material in this press release comes from the originating research organization. Content may be edited for style and length. Want more? Sign up for our daily email.

1 thought on “Barring Nonmedical Exemptions Increases Vaccination Rates, Study Finds”

  1. You fail to account for the thousands of parents who shifted to home schooling or moved out of the state due to this Fascist legislation. Only those who do not have the financial means to do either of these have been affected, and many of them are unhappy campers with good reason.

    Forcing the remaining parents to vaccinate their kids is a violation of the Nuremberg Code of Informed Consent. There is no such thing as vaccine induced herd immunity as all vaccines “wear off” in a few months to years. Hence vaccinated individuals now are susceptible to disease, which explains why 18 – 30% of vaccinated people in the Disneyland measles outbreak a few years ago.

    The only true herd immunity is when a population is exposed to the bacteria or virus, fights it off with their own immune system and now has 100% protection against future infections. No vaccine will ever do that because they do not activate the innate TH1 part of the immune system. They also overactivate the TH2 humoral immune system which explains why we have so many sick kids (asthma, allergies, autoimmune diseases) that we did not have when I grew up in the 50’s.

    Measles was a right of passage in my day which confirs additional protection against other diseases as an adult. The incidence of measles, polio, mumps, etc had fallen by 95+ % by 1963 well before vaccines were foisted upon us…….hence they have had NO effect on disease incidence.

    There have been no safety studies performed on any vaccine……..despite the NVICA mandating them. Pharma said “screw you” to the American public onc they got what they wanted………complete legal immunity against maiming and killing people. It’s the ONLY product in this country that has 100% legal protection against lawsuits……….unbelievable!

    Caveat Emptor!

Comments are closed.