Sunday, January 25, 2015

When it comes to measles, it is a small world after all

Dan Diamond wrote an essay recently in Forbes in which he notes the asymmetry of public reaction to Ebola versus measles. He describes how on the one hand, even though Ebola was unlikely to cause an epidemic in the US the public went nuts with Fearbola, while on the other hand measles represents a much more realistic threat of spread but people are somewhat apathetic about it. It seems a valid observation.

It may be difficult to understand public perception of threat when it comes to infectious disease, but, epidemiologically speaking, there are some important differences between the two, as partially summarized in the table below.



Measles Ebola
R0 ~7-18 ~2
Serial interval 8-12 days 5-15 days
Incubation period 10-12 days 2-12 days
CFR 3% 25-90%
Infectious period ~ 4 days before rash to several days after onset of rash At onset of symptoms
Vaccine preventable Yes No

Importantly, persons infected with measles virus are infectious before they begin to feel ill, so they are able to spread the virus in the course of their normal activities. Fearbola -- the epidemic of hyped and often unfounded messages surrounding the threat of Ebola to the US -- struck in part because of the high case fatality rate (CFR) and the lack of a vaccine conveying immunity to the Ebola virus. That contrasts strongly with measles. Even though the measles outbreak that started at Disneyland Resort Theme Parks in California is expanding, I doubt there will be a Fearmeasles epidemic, even though measles can be fatal and cause long term sequelae.

That said, this is a fascinating event due partially to people's attitudes regarding vaccines. Recently, the ramifications of such attitudes, in terms of implications for public health agencies, has been expressed very clearly by Lisa Aliferis (writing for NPR):
Local health officers in counties [in California] affected are busy tracing those who infected patients have been in contact with. Dr. Erica Pan, deputy health officer of Alameda County, says the county has shifted resources from Ebola preparedness to contact tracing for measles. Last year there were four cases of measles in Alameda County, she said, "but we had 400 contacts to investigate."
This is remarkable. On 23 January, the California Department of Health reported that in LA and Orange counties alone there were 31 confirmed cases. A simple back-of-the-envelope calculation suggests that if 4 cases required 400 contacts to be investigated (100 contacts per case on average), then 31 cases could require 3100 contacts to be investigated. No wonder health departments are refocusing resources away from Ebola and onto measles.

People who do not vaccinate their children, or catch up on missed vaccines as adults, do not only place themselves in danger of infection, they place the community in danger. Moreover, they cause scarce public health resources to be spent on controlling a vaccine preventable disease. It's ironic that the lyrics to It's a small world -- the theme song of a ride at Disneyland of the same name -- read
It's a world of laughter, a world of tears.
It's a world of hopes and a world of fears.
There's so much that we share,
That it's time we're aware
It's a small world after all. 
Indeed.

(image source: Wikipedia)

3 comments:

  1. Horace Boothroyd IIIJanuary 30, 2015 at 9:44 PM

    What bothers me about the antivaccine loons is that their health depends on my getting the vaccine and doing my bit to establish herd immunity. We all know that there is a tiny bit of risk attached to getting the shot (albeit much less than the risk of going unprotected) so I resent the fact that they are not only pumping up the risk of an outbreak but also taking a free ride on my willingness to do the right thing. What horrible, selfish people!

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  2. No, our health doesn't depend on your getting vaccinated. These "preventable" diseases are actually an important immune system mile-stone and convey long term healthier immune response in people. Immunizations to not work the same as acquired immunity and are inferior at protection. Did you know that there are some cancers that can be treated with measles? (glioblastoma, Mao Clinic: Hepatoblastoma, Pub Med: multiple myeloma, Mao Clinic) (Also interesting: psoriasis remission after measles, Pub Med) Please read a package insert for any vaccine. More important to health in society is clean water to drink, proper treatment of sewage and nutrition.

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  3. The two comments clearly represent divergent views. As I've advocated previously, I don't believe it's constructive to engage in name calling. I agree that safe food and water, and good sanitation engineering, are among the determinants of health, and that herd immunity results in protection of those who are vulnerable to infection. It's less clear to me that vaccine-associated immunity conveys a less-healthy immune response than does disease-associated immunity. In what ways does natural infection result in a "long term healthier immune response"? Many vaccines produce robust long-lived immunity. Regarding the issue of measles viruses as potential/investigational cancer therapies, Russell and Peng (http://www.ncbi.nlm.nih.gov/pubmed/19203112) describe how a major impediment to the successful deployment of oncolytic measles viruses is the high prevalence of preexisting anti-measles immunity. Measles in the pre-vaccine era was known as a "childhood disease" because the vast majority of the population that survived to adulthood was immune to it as the result of childhood disease. Thus, it's difficult to imagine that vaccine-associated immunity is more of an impediment to this potential therapy than natural disease-associated immunity (i.e., if the vaccine had never been invented).

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