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Measles outbreaks occur even when the vaccinated population exceeds 95%

“If you only risked your own health by not getting vaccinated, that would be your business,” mass vaccination advocates state. “But when your failure to get vaccinated endangers me or my child, that becomes my business.” It’s a powerful argument, except for one thing — herd immunity in vaccinated populations has been repeatedly disproven.

In November 1966, in announcing a mass vaccination program for measles that would exceed the 55% level reached in Baltimore, the U.S. Public Health Service confidently announced that “Effective use of these vaccines during the coming winter and spring should insure the eradication of measles from the United States in 1967.”

When measles failed to be eradicated, public health experts decided that a 70% or 75% vaccination rate would secure herd immunity. When that proved wrong, the magic number rose to 80%, 83%, 85%, and then it became 90%, according to a 2001 Health Services Research report. Later health experts commonly cited 95%.

But that too was insufficient — measles outbreaks occur even when the vaccinated population exceeds 95%, leading some to say a 98% or 99% vaccination rate is needed to protect the remaining 1% or 2% of the herd. But even that may fall short, since outbreaks occur in fully vaccinated populations.

“The target would be to have 100% of the population vaccinated,” Dr. Gregory Taylor of the Public Health Agency of Canada recently told CBC, voicing an increasingly common perspective among public health professionals. At that point, the balance of the herd that would be protected through mass vaccination would be precisely 0.