President Trump speaks before signing an executive order that calls for changing the childhood vaccine schedule.

Jim Watson/AFP via Getty Images

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Jim Watson/AFP via Getty Images

This is a developing story that will be updated.

President Trump signed another executive order aimed at trying to upend the way U.S. children are vaccinated against dangerous infectious diseases.

The new executive order, signed Monday afternoon in the Oval Office, calls for reducing the number of childhood vaccines recommended by the federal government.

It also calls for breaking up the shot known as the MMR, which is now given as a single vaccination for measles, mumps, rubella and chickenpox. The order advises breaking it up into separate shots.

The order also directs the Justice Department to pressure states to reduce the number of vaccines required for school.

The moves will likely be challenged in court, as previous similar attempts to change the childhood vaccination schedule have been.

At the signing ceremony, the president talked about vaccines needing to be studied in light of rising autism rates, a thoroughly studied and debunked theory.

The news was welcomed by vaccine critics and denounced by many public health experts.