WEDNESDAY, Sept. 19 (HealthDay News) -- Nonmedical exemptions for school vaccination requirements have increased since 2005, particularly in states with easy exemption policies, according to a letter to the editor published in the Sept. 20 issue of the New England Journal of Medicine.

Saad B. Omer, M.B., B.S., Ph.D., from Emory University in Atlanta, and colleagues analyzed data from the U.S. Centers for Disease Control and Prevention for school years 2005 to 2006 through 2010 to 2011 to determine the annual rate of nonmedical exemptions from school immunization requirements, comparing the rates in states that allowed philosophical exemptions and states that allowed only religious exemptions.

The researchers found that the unadjusted rate was 2.54 times higher in states that allowed philosophical exemptions compared with those allowing only religious exemptions. However, the average annual rate increase was 1.20 in states that allowed only religious exemptions, compared with only 1.10 in states allowing only philosophical exemptions. Unadjusted rates of nonmedical exemptions were 2.31 times higher in states with easy exemption policies compared with those with difficult exemption policies. The average annual rate increase was 13 percent in states with easy policies, reaching 3.3 percent in 2011, compared with an 8 percent increase in states with difficult policies, reaching 1.3 percent in 2011.

"In an earlier analysis of data from 1991 through 2004, we found an increase in exemption rates only in states with philosophical exemptions and in states with easy exemption procedures," Omer and colleagues write. "Our results show that nonmedical exemptions have continued to increase, and the rate of increase has accelerated."

The study was partially funded by an unrestricted educational grant from Merck.

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