There isn’t a lot of research on children’s safety when a child is on an alternative vaccine schedule. While we clearly know that the longer you wait to immunize a child for vaccine-preventable illnesses, the longer the window of time a child is left susceptible, there isn’t a huge data set on children who are late to get shots or who are considered “undervaccinated.” Although it’s intuitive to think that a child who is not getting immunizations on time is at higher risk for infections (particularly during times of epidemics), it’s helpful when the science backs up our instinct and thinking.

This is likely something you already knew but there’s new research to compound our understanding.

Children Late On Shots Are At Risk For Whooping Cough

Recent pediatric research found that when it comes to whooping cough, children who were late on getting their shots are more prone to infection. In fact the more doses of the DTaP shot that a child misses, the more likely it is that they could be diagnosed with whooping cough.

A JAMA Pediatrics study published online in September 2013 evaluated children between 3 months to 36 months of age. During the first three years of life children are recommended to have 4 doses of the DTaP (Diphtheria, Tetanus, and Pertussis) shot starting at 2 months of age. In the JAMA matched case-control study children who were late on 3 doses of DTaP were 18 times as likely be diagnosed with whooping cough compared to children who were up to date on their shots. Children unvaccinated (missing 4 doses of DTaP) were 28 times more likely to be diagnosed with whooping cough when compared with fully vaccinated children.

The takeaway reminder? When you start a series of immunizations for your children, make sure you complete all shots in the series. Most experts believe children aren’t fully protected from whooping cough until they’ve received 4 doses of DTaP (at 15 months of age if on-schedule).

We have to finish what we start — another reason to get in on-time for well-care visits during the first few years of a your child’s life. And as a final note, the value of well-child care extends well past immunization.