Los Angeles, California - Liberal states led by California on Tuesday said parents should continue to get their children immunized, contradicting what they said was "dangerous misinformation on vaccines and autism" issued by the federal government.

The West Coast Health Alliance said it was "deeply concerned" by the anti-science mood that has overtaken the Centers for Disease Control under the leadership of vaccine skeptic Health Secretary Robert F. Kennedy Jr.

"Rigorous research of millions of people in multiple countries over decades provides high-quality evidence that vaccines are not linked to autism," said a statement from the alliance, which groups California, Oregon, Washington, and Hawaii.

"Autism is a complex neurodevelopmental condition with multiple contributing genetic and environmental factors. Suggesting it stems from any single cause, such as vaccination, misleads families who deserve accurate guidance."

The intervention comes after the CDC revised its website, using language that undermines its previous, scientifically grounded position.

The new language accuses health authorities of having "ignored" research supporting a link and said the US health department "has launched a comprehensive assessment of the causes of autism."

A purported connection between the measles, mumps, and rubella vaccine and autism stems from a flawed study published in 1998, which was retracted for including falsified data.

Its results have not been replicated and are refuted by voluminous subsequent research.

Kennedy has a long history of promoting dubious claims, many of which have become articles of faith among adherents to his "Make America Healthy Again" movement, a vital part of President Donald Trump's fractious Make America Great Again coalition.

The website edits last week were met with anger and fear by career scientists and other public health figures who have spent years combating such false information.

The West Coast Health Alliance came together in September in an effort to counter what many Democrats see as a dangerous turn towards conspiracy theories in the highest reaches of the US government.

Organizers say it is intended to "safeguard scientific expertise" and ensure public policy is informed by trusted and qualified voices.

"Through this partnership, the four states will coordinate health guidelines by aligning immunization recommendations informed by respected national medical organizations, allowing all people in the United States to receive consistent, science-based recommendations they can rely on – regardless of shifting federal actions," they said.