California Gov. Jerry Brown has signed into law a mandatory vaccination law for the state's schoolchildren, one of the toughest such measures in the U.S.

The new law removes the option for parents to request exemption from the state's vaccination requirement for their children based on religious or personal beliefs.

Under the legislation passed by both the state Senate and Assembly and now bearing the governor's signature, children entering California schools or day care programs must receive vaccinations for diseases such as measles and pertussis, also known as whooping cough.

Before its passage, the legislation was modified to leave standing certain medical exemptions for conditions such as compromised immune systems that could make being vaccinated dangerous, but a physician must confirm such a condition.

Most families will now face a choice; either have their children vaccinated or face the prospect of having to home-school them.

While the legislation was strongly supported by the medical profession and many parents, many others opposed it, saying the decision of whether or not to vaccinate a child belongs with the parents and expressing fears about the safety of vaccines.

Opponents say they will take legal action to overturn the law, even though courts, including the Supreme Court, have come down on the side of vaccination requirements.

Brown, while acknowledging the opponents, had made their opinions known with "eloquence and sincerity, made his position clear in a statement.

"The science is clear that vaccines dramatically protect children against a number of infectious and dangerous diseases," he said. "While it's true that no medical intervention is without risk, the evidence shows that immunization powerfully benefits and protects the community."

Bill author State Senator Richard Pan, a Sacramento Democrat who is also a pediatrician, expressed thanks to the governor for "listening to the science and the people of California."

Pan introduced the vaccination bill after an outbreak of measles at Disneyland in December of last year that infected more than 100 people.

The new law makes California just the third U.S. state, after Mississippi and West Virginia, to completely eliminate religious and personal belief exemptions from vaccinations.

As in most states, California had mandated vaccinations as a requirement for school entry decades ago to prevent childhood diseases, including polio, whooping cough and measles. However, those original mandates gave parents the opportunity to opt out on personal or religious grounds, an option now removed under the newly-signed law.

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