Delayed vaccination was an anti vax talking point awhile back: Somehow parents were convinced by morons on the internet that you had to space vaccines out more. Basically once you start questioning the actual science, the more susceptible you are to just never actually finish the vaccine series, so antivaxxers win.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2882604/

Intentionally delayed vaccine doses are not uncommon. Children whose parents delay vaccinations may be at increased risk of not receiving all recommended vaccine doses by 19 months of age and are more vulnerable to vaccine-preventable diseases. Providers should consider strategies such as educational materials that address parents’ vaccine safety and efficacy concerns to encourage timely vaccination.

I’d like to point out that ISIL took responsibility.

Only if Russia and Iran agree and do it simultaneously.