Agency says results show why it recommends kids get an updated shot.

Children who received an original COVID-19 vaccine have little protection against hospitalization just months after vaccination, according to a new study from the U.S. Centers for Disease Control and Prevention (CDC).

Children initially have 52 percent protection against hospitalization but that estimated effectiveness plummeted to 19 percent after four months, according to the paper.

Protection against so-called critical illness also dropped sharply, from 57 percent to 25 percent, researchers found.