Measles!

Ah, there's no end-bold tag at the end of this post, so it's putting everything after it in bold....

Someone needs to tell the antivax folks that the only way the herd immunity phenomenon protects their children from disease is that a significant portion of the population be properly immunized.

Herd immunity did not help anyone in the current situation. Foreign exposure trumps herd immunity unless you mandate that everyone on the planet be vaccinated on the day they are born.

I would argue that herd immunity actually did help, in that it prevented more widespread dissemination. My brother was impacted by the San Diego outbreak and gave me a little more background. An antivax woo-family brought their unvaxed kids on a third-world vacation to an area where measles was endemic, where one of the children contracted measles. They returned, and while still in the latent, contagious phase, said child returned to his charter elementary school, which contained a disproportionate number of unvaxed woo-kids (their parents attracted to this school by a lack of mandatory vaccinations), wherein it spread to other woo-kids. One of the little woo-sibs shared daycare with my brother's 6-month-old, who had not yet completed his mmr series. Long story short, 2 weeks of house-quarantine (lost work for my brother and his wife, their other kids kept home), and fortunately my nephew didn't contract measles.

As I look at the scenario, there was a local outbreak, which I would guess (not knowing for sure) was comprised mostly/entirely of unvaccinated people (woo or too young to have completed the series.) Given the latency period and the exponential spread of something like this in a vunerable population (I transmit to 20 people, they each transmit to 20 people, etc...), I would attribute the relative containment to herd immunity in the greater San Diego population(and to a lesser degree to the actions of the local public health department in quarantining those potentially exposed.)

in this case the "third-world" was Switzerland but I take your point since they have a less-than-WHO standard vacc rate for measles. herd immunity probably kept it damped down. responsible people contained the effects of irresponsible people.

SurgPA said "my brother's 6-month-old, who had not yet completed his mmr series"

Actually, a child under age one would not have even started the MMR series. The first one is given between 12 to 15 months, and the second one at around 4 to 5 years old.

(my oldest got his second one prior to entering 6th grade, before the timing was last revised, but I got my younger kids theirs when they were 5 and 8 years old because there was a measles outbreak at a local private school)