Whenever there are cases of measles, or any childhood illness that has a vaccine, the immediate blame falls on parents who refuse to vaccinate their children. (Pittsburgh editorial)
In the U.S. the rate of refusal of vaccines by parents is less than 2%. (CDC 2010) Given that outbreaks often include both vaccinated and unvaccinated individuals, it is clear that the transmission of measles can take place between vaccinated individuals.
While it is enticing to simply blame outbreaks of measles on unvaccinated individuals, the reality is that the vaccine itself is not fool proof, and may provide varying immunity based even on the timing of the vaccination. “Vaccine efficacy rose from 85% in children vaccinated at 12 months of age to > or = 94% in those vaccinated at 15 months and older.” (study here)
Rather than focusing on the tiny percentage of parents refusing vaccination, public health dollars and attention should be focused on the evolving threat of measles in a vaccinated world. Studies from France found that health care workers who had been vaccinated still contracted measles, and likely passed on the virus to their charges (below). Even after mandatory universal vaccination, Singapore still sees a few cases of measles. They also see a large number of false positive diagnoses, where the majority of cases diagnosed as measles are not that virus at all.
Measles represents the most highly effective vaccine within its MMR combination. The mumps component has at best 88% efficacy (below), making the primary problem with its transmission the strength of the vaccine rather than the resistance of parents.
Ann Dermatol Venereol. 2011 Feb;138(2):107-10. Epub 2011 Feb 1.
[Measles in adults: an emerging disease not sparing medical staff].
Monsel G, Rapp C, Duong TA, Farhi D, Bouaziz JD, Meyssonnier V, Mirkamali A, Jaureguiberry S, Caumes E.
“We retrospectively studied all the consecutive cases of measles seen in adults between the 1/1/2007 and the 30/4/2009 in four Parisian hospitals.Twenty-one patients were included. Six patients (29%) were health care workers (HCW) including five (83%) who were vaccinated.”
Euro Surveill. 2010 Sep 9;15(36). pii: 19656.
Spotlight on measles 2010: update on the ongoing measles outbreak in France, 2008-2010.
Parent du Châtelet I, Antona D, Freymuth F, Muscat M, Halftermeyer-Zhou F, Maine C, Floret D, Lévy-Bruhl D.
“Since early 2008, France has been experiencing a measles outbreak with almost 5,000 notified cases as of 30 June 2010, including three measles-related deaths. The proportion of cases 20 years or older reached 38% during the first half of 2010. This situation is the consequence of insufficient vaccine coverage (90% at age 24 months in 2007) that led to the accumulation of susceptibles over the last years.”
Southeast Asian J Trop Med Public Health. 2006 Jan;37(1):96-101.
A 24-year review on the epidemiology and control of measles in Singapore, 1981-2004.
Ong G, Hoon HB, Ong A, Chua LT, Kai CS, Tai GK.
“Vaccine efficacy of the trivalent MMR vaccine based on institutional outbreak investigations was consistently above 92%. We also found that the overall seroprevalence of the population to measles has decreased from approximately 91.5% in 1989/1990 to 1993 to 77.9% in 1998 (mainly in children < 4 years old) and that only 7% of clinically notified cases of measles were serologically confirmed to be positive for measles.””
Singapore Med J. 2007 Jul;48(7):656-61.
Outbreak of measles in primary school students with high first dose MMR vaccination coverage.
Ong G, Rasidah N, Wan S, Cutter J.
“Indigenous cases of measles continue to occur in Singapore despite the implementation of a two-dose mumps, measles and rubella (MMR) vaccination policy in 1998… The attack rate was 1.2 percent in the vaccinated group and 53.8 percent in the unvaccinated group.”
Bull Acad Natl Med. 2010 Apr-May;194(4-5):719-32; discussion 732.
[Consequences of opposition to vaccination in France and Europe. How to maintain effective vaccine coverage in 2010?].
[Article in French]
“Low vaccine coverage can lead to the persistence of preventable diseases and, in some cases, to a dangerous shift in the age of pathogen encounter towards adulthood. This is the case of measles in Europe, where some countries, including France, have not reached the effective vaccine coverage rate of 95%.”
CMAJ. 2011 May 16. [Epub ahead of print]
An assessment of mumps vaccine effectiveness by dose during an outbreak in Canada.
“Vaccine effectiveness of one dose of the MMR vaccine ranged from 49.2% to 81.6%, whereas vaccine effectiveness of two doses ranged from 66.3% to 88.0%. If we assume vaccine effectiveness of 85% for two doses of the vaccine, vaccine coverage of 88.2% and 98.0% would be needed to interrupt community transmission of mumps”