[josephv]

Vaccination doesn't 100% guarantee immunity, so there is always a % that isn't immune. Each disease requires a different % immunity to prevent a wide-spread outbreak, i.e. to provide herd immunity. For particularly aggressive diseases it requires 95ish% immunity to avoid an outbreak.

So with anti-vaxxers increasing from roughly .5% to 1.5% over the last 10 years or so, that introduces a significant increase in the requirement of vaccination effectiveness, to the point where you wonder are we close to herd immunity breaking down.

In places with significant anti-vax sentiments, such as ultra-orthodox religious practices you will get those larger outbreaks of things like measles.

In general I think research indicates in the general populous anti-vaxxer populations are still small and disparate enough as to not impact herd immunity, but the trend has been upward due to the anti-vax trend over the last decade.

[source] am married to an M.D. that specialized in microbiology, recently listened to a good NPR bit about it that dropped the statistics, and I stayed at a holiday inn express last night.