A nurse administers a measles vaccine to a boy in the U.K. Anti-vaccine advocates are active in nearly all developed countries -- not just in the U.S. Rebecca Naden/Reuters

Even as the worst rash of measles in 15 years takes hold in California, pockets of anti-vaccination resistance remain throughout the U.S. and in every developed nation. Vaccines have proven time and again to be a safe and effective way to protect people against deadly disease outbreaks. When these eruptions do occur in developed countries that are more than capable of fully preventing them, public health experts point fingers at parents who refuse to vaccinate their children for personal reasons.

"I think all countries have dealt with this over the last 10 to 15 years to some extent," says Jason Schwartz, an ethics researcher who focuses on health policy at Princeton University.

The entire anti-vaccine movement, in fact, has foreign roots. A widely discredited (and eventually retracted) paper published in The Lancet by former medical researcher Andrew Wakefield suggested a link between the measles vaccination and autism. After it was published in 1998, vaccination rates in the U.K. plummeted. Fifteen years later, the government instated a national "catch-up" plan to try to vaccinate about a million teenagers who had missed early childhood vaccinations. That same year, in 2013, measles broke out in the city of Swansea, Wales for eight months and sickened 1,455 people there.

Public health officials across the globe consider the anti-vaccine sentiment a serious threat, and have tried to weed it out whenever possible. In Australia last year, the government forced a prominent group of anti-vaccine advocates formerly known as the Australian Vaccination Network to change its name to the Australian Vaccination Skeptics Network for fear that the original title was misleading to parents who came across the group’s campaigns. Now the group is busy trying to start a fake religion so church members can claim religious exemption from vaccination. It costs $25 to join. The Guardian reports that the parent organization’s membership has declined, however, from 2,042 members in 2011 to just 418 in 2013.

Official policies for recommending or requiring the measles vaccine vary widely—even between developed countries. Australia, for example, uses tax incentives to encourage parents to vaccinate children and hosts a national registry to make it easier for government officials to keep track of shots. Politicians in Victoria and New South Wales have passed "no jab, no play" laws that prohibit kids who are not fully immunized from enrolling in childcare.

In Saudi Arabia, parents do not receive a birth certificate until their child's first birthday, and only if mandatory vaccines have been administered. "Basically, you don't exist until you get the recommended vaccine," Paul Offit, director of the Vaccine Education Center at the Children's Hospital of Pediatrics in Philadelphia who has also written a book on the discredited link between autism and vaccines, says. "I like that."

Measles outbreaks continue to occur in all of these countries. Just last week, health officials in Canada detected at least four cases of measles in Toronto. None of the victims had been vaccinated. Meanwhile, a professor at Queens University in Ontario was called out by students for incorrectly teaching that vaccines can cause cancer and AIDS. Ontario is one of only two provinces in Canada, which require children to be vaccinated for measles before they start school. In all others, vaccination is voluntary.

Here in the U.S., states require a host of vaccinations for diseases including measles by the time a child enters school or attends childcare. Therefore, U.S. vaccination rates are fairly high—in the neighborhood of 80 to 90 percent of the population for most vaccines.

"We're one of the few countries that has vaccine mandates," Offit says. "Most countries certainly in western Europe don't. As a consequence, measles are to a large extent endemic in western Europe." The measles vaccine was created in 1963 and widely distributed in 1968. By 2000, measles had been eradicated from the United States.

The entire promise of vaccines relies on the notion of herd immunity—the idea that if the majority of people within a population are vaccinated for a disease, it cannot easily spread among them. In general, vaccination experts say a group has achieved herd immunity if 95 percent of the population is vaccinated. People who do not vaccinate poke holes in that immunity by providing a sanctuary for diseases to take hold. The more people there are like this, the more at risk the rest of the population becomes.

Though vaccine safety and efficacy is proven, Offit realizes opponents around the world are still wary to accept mandatory vaccines as willingly as, say, car seat laws. "You're asking citizens to give as many as 26 inoculations [to their child] in the first few years of life and as many as five shots at one time, of a biological fluid they don't understand," Offit says. "I don't think it's surprising there's pushback."

Even within the U.S., the vaccine requirements enforced by states have varying degrees of rigor which may be exploited by those who do not wish to give their children a vaccine before starting school. In every state, a child may be exempt for medical reasons such as immunodeficiency. Almost all states—except Mississippi and West Virginia—permit families to opt out for religious reasons. And 20 states—including California—also allow exemptions for philosophical or moral beliefs.

States with looser exemptions inevitably wind up with more cases of vaccine-preventable illness, says Ross Silverman, a health policy expert at Indiana University - Purdue University Indianapolis who published an article on this topic on January 20 in the Journal of the American Medical Association. This principle does not seem to hold true for countries—Sweden and other Scandinavian countries enjoy extremely high rates of vaccination with no requirements in place. "I can only imagine that they believe that their public health officials and government leaders trust them to do no harm," Offit says.

The majority of people who have been sickened in the Golden State from the current measles outbreak have not been immunized. In 2013, more than 17,000 kindergartners in California received a philosophical exemption from vaccine requirements which was more than three percent of all the children in the state who were entering school that year. A child who is not immunized is 35 times more likely to contract measles then a child who is, says Offit. "Fortunately, there's still an overwhelming number of parents that vaccinate their children," Schwartz adds.

Both Schwartz and Silverman recommend tighter restrictions on who can receive an exemption in the U.S. "Right now, they're so easy to obtain -- in some cases, it's not more difficult than signing a form or checking a box," Schwartz says. Silverman adds that California and Washington have both recently added an "informed-approval process" which requires parents to receive information on the risks of not vaccinating their children before they are granted an exemption, and that both states have seen a drop in the number of exemptions sought for philosophical reasons.

Offit says these measures would be a step in the right direction, but still he says he wishes vaccination were compulsory in the U.S. and around the world without allowances for parents to claim philosophical and moral exemption. "It shouldn't be their choice to allow their child to die of a preventable and treatable infection," he says.