DENVER — An effort to improve Colorado’s child vaccination rate, among the lowest in the country, sputtered Tuesday when lawmakers moved forward with a watered down bill.

When House Bill 1288 passed the House and went to the Senate, it would have forced parents to watch an educational video about the benefits and risks of vaccinations or get permission from a doctor before opting their child out of being vaccinated.

But the outcry from parents resistant to state-mandated vaccinations was finally heard in the Senate, where lawmakers Tuesday took those pieces out of the bill, which now only forces school districts to report vaccination rates.

The bill’s sponsor, Sen. Irene Aguilar, D-Denver, is a physician who spoke about the “misinformation” about immunizations causing developmental problems and argued that Colorado’s low vaccination rate is partly to blame for recent whooping cough outbreaks.

But, in the end, she didn’t have the votes.

Current state law requires only a parent’s signature to claim a personal, medical or religious exemption from vaccination, with the majority of exemptions for personal reasons.

The amended bill now must go back to the House, where lawmakers will have to sign off on the changes.

Rep. Dan Pabon, D-Denver, the House sponsor, said Tuesday he doesn’t plan to fight over the Senate changes with just two weeks left in the legislative session.