You’ve probably read that certain vaccine-preventable diseases like measles and whooping cough are making a comeback. (The first four months of 2014 saw more measles cases than in any year since 1996.) Breakouts tend to be focused in communities where there are large pockets of parents who choose against immunizing or delay it, out of religious or personal beliefs (like that shots trigger autism, despite rigorous research showing otherwise). This “opt out” trend has gotten a lot of press lately, but there’s another, less newsworthy reason why many parents aren’t getting their kids vaccinated on time: They just haven’t gotten around to it.

Last year, a study sponsored by the Centers for Disease Control (CDC) revealed that 49% of some 300,000 toddlers in managed care programs were late on certain immunizations by their second birthday. But only about 1 in 8 of those kids were undervaccinated due to “parent choice.” Most were likely behind due to logistical issues, such as missed well visits and sickness at the time of a scheduled appointment, said researchers in a Reuters report on the study. HHK advisory board member Julie Kardos, M.D., who runs a pediatric clinic outside of Philadelphia, has seen this phenomenon—and its possible repercussions—up close. One of her patients was a four-year-old boy who was behind on his vaccines, and was hospitalized for pneumonia. Before measles was identified as the cause, he exposed an entire E.R. to the illness, which is one of the most contagious diseases there is. (As Dr. Kardos and Naline Lai, M.D. write in their Two Peds in a Pod blog,  nine out of 10 unvaccinated people get sick from exposure to measles, and are contagious before symptoms begin.)

Photo by: Dawn Huczek

What scares me is that this type of scenario seems pretty plausible. There are an incredible number of vaccines to keep track of now—the CDC now recommends immunizations against 16 preventable diseases, and a child could realistically have had 24 vaccines administered by age 2. Plus, many days, our family’s collective schedule seems like a deck of cards, and one false move—misplaced car keys, say—can cause everything else to topple. I can see how many parents could believe fully in the importance of vaccines, but feel they can put them off—and off, and off some more—until work slows down or Billy gets over his cold (and do toddlers ever really get over their colds before another one starts?). Even more convincing are the moms and dads who, due to multiple jobs or a lack of easy transportation, feel like they literally can’t get their child to the doctor’s office, despite their best intentions.

The thing is, every single person in the community is responsible for keeping vaccine-preventable diseases at bay. When even just around 10% of kids miss a vaccine against certain illnesses, so-called “herd immunity” against that bug is compromised, and something as minor as one undervaccinated child’s exposure to an infected person in an airplane, mall or doctor’s office can cause an illness to seep into a community. (I wrote more extensively on this topic in a Parents magazine article a couple years ago.) And these vaccine-preventable illnesses are no joke: Measles, for instance, can not only cause pneumonia, but encephalitis, which can lead to permanent brain damage. Keeping on track with vaccines is key, and especially when your child is young, says Dr. Kardos. For toddlers and preschoolers, shots are numerous and frequent not because doctor’s want to torture them (or us), but because their growing immune systems are more vulnerable to illness.

Dr. Kardos suggests printing out the CDC immunization schedule (filter by your child’s age and your favorite format—even tri-fold!— here) and keeping it on your ‘fridge or bulletin board or in your wallet. There are also some new apps for your phone that can help you keep track. (I like Vaccines on the Go, an app put by the Vaccine Education Center at Children’s Hospital of Philadelphia). In most cases, doctors will remind you what vaccines your child needs once you show up to a well visit, but knowing the schedule in advance can help remind you just how important those regular visits are. It can also prompt you to pack a favorite book, lovey, or my personal savior, lollipop, in your diaper or tote bag when you know it’s going to be a “special” day at the doc’s office. Vaccines can be a pain—literally and otherwise—but few things you can do for your kid and community are more important.