Something strange is happening in America. Research shows fewer Americans are identifying with organised religion, but in pockets of the country, a seeming explosion in new-found faith borders on the miraculous.

Take Vermont, for example. After 2016, the number of families professing deep religious convictions spiked suddenly by over seven times, a new study shows. These families also had kindergarten-age children, and by all likelihood, this was not divine revelation.

So what was it? According to paediatrician Joshua Williams from the University of Colorado, it's most probably an unexpected side effect of tightened laws regulating the mandatory vaccination of school students in the state.

While vaccination is compulsory across the US for students attending school, the requirement is waived in cases of exemption.

For example, medical exemptions are available in every US state (and in Washington, DC), in instances where a medical condition means vaccination could be harmful to the student.

In 45 states, exemptions on religious grounds are permissible as well (despite the seeming contradiction that all major religions now encourage immunisation, and scriptural analysis suggests this has long been the case).

Just 15 states now offer personal belief or 'philosophical' exemptions, and the numbers of states offering religious and personal belief exemptions have dwindled in recent years, as lawmakers seek to curb the spread of dangerous infections.

A trailblazer in this regard was Vermont, in 2015 voting to become the first state to repeal its personal belief exemption, which became law in 2016.

In their new study, Williams and fellow researchers analysed Centers for Disease Control and Prevention (CDC) data on exemptions for children entering kindergarten from 2011 to 2018, to see how the removal of such personal belief exemptions might impact religious exemption rates.

In Vermont, this single policy change coincided with a huge increase in the proportion of kindergartener enrolments claiming a religious exemption – jumping from 0.5 percent of students to 3.7 percent.

"We interpret that as evidence of a replacement effect," says Williams.

In other words, the researchers contend that parents in Vermont who did not wish to vaccinate their children started to claim an objection on religious grounds, only because the former alternative – personal belief – became unavailable.

Of course, there's no way to prove that, but in their paper, the researchers cite a couple of small studies that suggest it could be happening at the level of individual parents.

"Furthermore, it is interesting to note that Vermont ranked 48th out of 50 in state religiosity in the year before its policy change," they write.

The hypothesis is strengthened by the researchers' finding that states offering both religious and personal belief exemptions were one-fourth as likely to have kindergarteners with religious exemptions, compared to states with religious exemptions only.

"Our hypothesis going in is that in states that offer both exemptions types, the rate of religious exemptions would be quite low, but that we would be able to see a significant difference then looking at religious exemptions in states that only offered religious exemptions," Williams told Stat.

"We were hoping that the state of Vermont would provide a nice case study of that… And that's exactly what we found."

While the result is somewhat jarring – and the suggested 'tactics switch' by anti-vaxxer parents runs the risk of obfuscating the already muddled reasons people use to justify a vaccine hesitant stance – the team does point out one piece of good news.

In Vermont, at least, the overall proportion of Vermont kindergarteners with non-medical exemptions decreased after the 2016 policy change (even while faux religiosity boomed).

"This finding aligns with aforementioned studies that showed lower overall non-medical exemption rates in states with religious exemptions only, and vaccine advocates will likely interpret this as a public health victory," the authors write.

"In the last year, 10 other states have enacted or proposed legislation to eliminate non-medical exemptions, and policy makers in other states could consider Vermont's experience as an instructive example when considering policy changes to decrease exemption rates."

The findings are reported in Pediatrics.