State law requires all New Jersey school children to get a battery of vaccinations when they reach a certain age. But parents are allowed to opt-out if they write a letter simply stating "immunization interferes with the free exercise" of their family's religious rights.

This loophole is too big and the risk to children's health is too high, says physician and state Assemblyman Herb Conaway, D-Burlington.

The Assembly Health Committee he chairs is expected to vote on his bill Thursday that would make parents explain specifically how vaccinations violate theirs family's religious beliefs.

The objections could not be based "solely on political, sociological, philosophical or moral views, or concerns about the safety or efficacy of the vaccination," according to the legislation.

Conaway said his district office phone is already ringing at a steady clip with parents' objections. Opponents -- many of who have openly expressed their fear over the safety of vaccines -- have killed the legislation since it was first introduced in the 2012-13 session, when Gov. Chris Christie was governor.

"We've walked over the coals before and the phone lines are ringing," Conaway said. "This is the process and people have a right to voice their opinion. We will hear them and take our time."

The full Senate passed the bill in 2012 but it never advanced beyond committee approval in the Assembly. The bill died in committee in the two sessions that followed.

Although he hasn't approached Gov. Phil Murphy's staff to promote the bill, Conaway said he is optimistic the legislation will pass. "I have been assured he does believe science ought to guide decisions involving health care," he said.

Public health experts say vaccines are one of the greatest success stories in American history -- so much so that most parents have never seen a child with measles, mumps, polio and the other diseases that were rampant generations ago.

Opponents argue that children suffers side effects but few ever hear about it because drugmakers are protected from lawsuits and the National Vaccine Injury Compensation Program compensates families.

Sue Collins, co-founder for the New Jersey Alliance for Informed Choice in Vaccination, which has fought the legislation for years, said she and other parents are dismayed by how quickly and quietly the Health Committee is moving on the bill. The legislation, (A3818) will be introduced and voted on Thursday, which is unusual.

"What's really concerning and troubling is the bill was added Thursday at 5 o'clock, leading into a religious holiday weekend, and backing up to spring break. Many families this would effect are not even here," Collins said. "Ethically and morally, it seems very clear this is designed to cut the public out of the process."

The bill, itself, is vague, Collins said. "Who is deciding whether the people's beliefs are valid but somebody else's beliefs may not be?"

In the 2016-17 academic year, 10,407 children cited religion as a reason not to get legally required immunizations.

This comprised just 2 percent of the 525,517, student population enrolled in pre-kindergarten, kindergarten, first grade, sixth grade and transfer students, according to the state Department of Education. But the number of students seeking religious exemptions has risen dramatically, with 1,641 students getting a pass in the 2005-06 academic year.

Susan K. Livio may be reached at slivio@njadvancemedia.com. Follow her on Twitter @SusanKLivio. Find NJ.com Politics on Facebook.