On Wednesday, the New York City Board of Health voted unanimously to approve a mandate requiring that all day care and preschool children under the age of five receive seasonal flu shots.

In a statement, the New York City Department of Health called the new rule a necessary measure to offset low immunization rates in an at-risk demographic. "Young children have a high risk of developing severe complications from influenza," officials wrote. "One-third of children under five in New York City do not receive an annual influenza vaccination, even though the vaccine safely and effectively protects them against influenza illness. Young children often pass influenza to other children and family members, who then spread the infection to others in the community."

The mandate, which marks the last in a rather long series of health initiatives launched by outgoing Mayor Michael Bloomberg, was brought before the Board in September. Under the new law, all children enrolled in city-licensed day care services and preschools will have to get the influenza vaccine during the virus’ peak season or face expulsion. The flu shot thus becomes the eighth vaccine to be added to the city’s list of mandatory inoculations for children under the age of 5. The immunization schedule also includes measles, mumps, rubella, whooping cough, and chicken pox.

Many New Yorkers have praised the new rule as a responsible move towards improved public health. "This is great news for children," Richard Kanowitz, who lost his four-year-old daughter to the virus, told CNN. "Had the same law been in effect when my daughter was alive in 2004, she'd be alive today. She would not have gotten the flu."

That said, a small group of activists says it is set to mount a legal challenge to the mandate as soon as it goes into effect. Denouncing the Board’s approval process as opaque and excluding, John Gilmore, director of the non-profit Autism Action Network, told reporters that the law would soon be history. "This was a very closed process," he said of the process that was preceded by at least one public hearing. "We will most likely be filing a lawsuit fairly soon to overturn this.” Autism Action Network is one of several organizations championing the authoritatively rejected claim that vaccines cause autism. 

“From a legal standpoint, we see this as similar to the soda ban,” he added, referring to the Board’s unsuccessful 2013 drive to reduce the size of New York City soft drink servings. Gilmore did not specify from which legal standpoint drink sizes and immunization appear similar.  

Although the mortality statistics of influenza are notoriously difficult to calculate, the National Institutes of Health (NIH) estimates that the virus kills about 36,000 of the 20,000 it hospitalizes each year. The Centers for Disease Control and Prevention (CDC) currently recommends that everyone get the vaccine every peak season. Pregnant women, children under 5, and people with preexisting medical complications are thought to be particularly vulnerable.