Measles & Herd Immunity

Measles Death Rates:

  • Prior to the Measles vaccine in 1960, the death rate from Measles was 1 in 500,000; 2 in a million.  That means that 99.9998% of individuals living in a fully vaccine-free US population did not die from Measles even though it was estimated that 5 million people contracted Measles that year. CDC source “Vital Statistic and Rates in the US 1940 – 1960” pages 85 and 547 (https://www.cdc.gov/nchs/data/vsus/vsrates1940_60.pdf )
  • When the first ineffective and problematic measles vaccine was introduced in 1963 (with a second vaccine introduced in 1968), the rate of deaths attributed to measles had already declined by over 95%—between 1920 and 1962—and was continuing its downward trajectory. (https://www.cdc.gov/mmwr/preview/mmwrhtml/00056803.htm)

Herd Immunity

  • After herd immunity and subsequenct eradiation was not obtained via the measles vaccination program by 1978, the CDC set a goal to eliminate measles from the United States by 1982. This was primarily due to the understanding that herd immunity is much harder to obtain via vaccination as opposed to from natural immunity. Hence eradication efforts were abandon in the US. (https://www.cdc.gov/measles/about/history.html)
  • In the 1990’s measles was still not eradicated or eliminated. Poland and Jacobson, (1994) discussed the limitations of the 1-dose vaccines concluding, “The apparent paradox is that as measles immunization rates rise to high levels in a population, measles becomes a disease of immunized persons. Because of the failure rate of the vaccine and the unique transmissibility of the measles virus, the currently available measles vaccine, used in a single-dose strategy, is unlikely to completely eliminate measles. The long-term success of a two-dose strategy to eliminate measles remains to be determined.” (https://www.ncbi.nlm.nih.gov/pubmed/8053748)
  • Measles was finally declared eliminated (absence of continuous disease transmission for greater than 12 months) from the US in 2000 although there were 86 confirmed cases that year. (https://www.cdc.gov/measles/about/history.html)
  • In 2012 Poland and Jacobson addressed the “Re-Emergence of Measles in Developed Countries” despite the implementation of the 2-dose vaccination. Key points from their study include (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3905323/)
  • “Multiple studies demonstrate that 2–10% of those immunized with two doses of measles vaccine fail to develop protective antibody levels, and that immunity can wane over time and result in infection (so-called secondary vaccine failure) when the individual is exposed to measles.”
  • “For example, during the 1989–1991 U.S. measles outbreaks 20–40% of the individuals affected had been previously immunized with one to two doses of vaccine” and in the October 2011 outbreak in Canada, over 50% of the 98 individuals had received two doses of measles vaccine.”
  • “This leads to a paradoxical situation whereby measles in highly immunized societies occurs primarily among those previously immunized.”
  • “Our current tool for prevention has limitations that increasingly look to be significant enough that sustained elimination, much less eradication, are unlikely. Perhaps it is time to consider, in earnest, the development of the next generation of measles vaccines.”

Finally, it has been shown that during outbreaks some infected individuals developed measles as a result of vaccination. This infection is called a “vaccine reaction” but doctors can not differentiate between the “vaccine reaction” and a wild Measles infection without genetic testing. (https://jcm.asm.org/content/jcm/55/3/735.full.pdf)