Scare stories and MMR vaccine: What if there is a measles outbreak?

November 1, 2010 at 11:53 am (Anti-Vaccination) (, , , , )

Guest blog post from WH

The What Doctor’s Don’t Tell You website is up with a new scare story about MMR vaccine. The scare story itself has been debunked but let us take a look at the advantage that MMR vaccine provides by preventing measles and what will happen if the vaccine coverage decreases.

There has been a study by the good people of the Health Protection Agency examining the potential for measles transmission in England. The study concluded that even allowing for considerable underreporting of vaccine coverage, several districts have the potential for sustaining measles transmission.

The study was a well-conducted analysis; the methods were rigorous and well-reasoned and it deserves a closer look. In the study, the data about vaccine coverage was collected from COVER (Cover of Vaccination Evaluated Rapidly) programme between 1995 and 2002 and from primary care trusts between 2002 and 2006. The authors had accounted for missing and anomalous data. They had also performed a sensitivity analysis to estimate the under-reporting of vaccine coverage which came out around 24%. So the data collection technique of the study was robust.

Then the authors found the proportion of the population susceptible to measles according to age group using the following technique –

Proportion susceptible = 100% * proportion with 0 doses + 10% * proportion with 1 dose only + 1% * proportion with 2 doses.

This is a very good estimation when we consider the effectiveness of the MMR vaccine.

The potential for the transmission of measles and the size of the outbreak was estimated using the effective reproduction number. Effective reproduction number (R) is the average number of secondary cases per primary case seen in a population with an infectious disease. Secondary cases are all those cases that come in contact with the primary case and subsequently develop the disease within one incubation period. The value of the effective reproduction number determines if an outbreak will be sustained. If R>1, the outbreak will perpetuate, if R<1, the outbreak will die out and if R=1, the number of cases will remain same. Vaccination prevents the occurrence of an outbreak by keeping R below 1. More information about effective reproduction number is available here. [Note: link goes to PDF] The estimation of R was done using the Next Generation Matrix (NGM). More about NGM is here.

Here is a graph showing the percentage of children susceptible to measles prepared from the data available in the study –

As much as 27% of the children in the pre-school age group are susceptible to measles. In their analysis, the authors found that 4 Strategic health Authorities (SHAs), all in London has the potential for measles outbreak with the highest R value in South West London. They also estimated outbreak sizes in case of a possible outbreak of measles. Here is a graph showing outbreak sizes considering 30% under-reporting of vaccine coverage –

When we add the complications of measles to this, the picture looks grimmer. More detailed analysis is available in the paper.

If the vaccine coverage remained stable since 2004/05, the size of the R value still continues to increase each year raising the potential of an outbreak and increasing the size of a possible outbreak.

It is a ticking time-bomb unless measures are taken to increase the coverage of MMR vaccine to reduce the R value below 1. Scare stories such as those of WDDTY have the potential to do much harm and absolutely no good.

Thanks to jdc for hosting.

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5 Comments

  1. dt said,

    Good, reasoned analysis.
    A good source for vaccination coverage is WHO.
    Between country comparisons can be made, showing how pants the UK is compared to other countries.

    http://apps.who.int/immunization_monitoring/en/globalsummary/countryprofileresult.cfm

    WDDTY is a heap of drivel. Of course doctors don’t tell their patients that stuff – to do so would be misleading and cruel, if not downright lies.

  2. Oliver Dowding said,

    There may be something in what is offered here.
    But wish I had confidence that doctors et al were recording all the adverse reaction accurately and completely – they aren’t…..my son for one (assuming I didn’t imagine the violent immediate reactions.

    Two interesting observatgions – which you will forgive me for not being a scientist who can present data as you would. 1 in 166 American children is being diagnosed autistic. They probably receive more vaccines than any children in any country. Why?

    The Amish (sub-set) don’t allow vaccines and barely know what autism is. Why?

    We all know surely that the best innoculum for a child is mother’s milk. Yet medical folk think it’s necessary to vaccinate children being breast-fed. Why?

    Think about the experience with The Hopewood Children. http://www.vaclib.org/basic/unvaxhealth.htm#hopewood How did that happen? Why did they do so well without any vaccines?

  3. WH said,

    Sorry to hear about your son. The measles antibodies derived from mother persists approximately up to 12 months of age, that’s why the first MMR vaccine is recommended to be given when children are 13 months old when maternal antibodies do not provide immunity anymore (http://hcd2.bupa.co.uk/fact_sheets/html/mmr.html#2).

    The claim regarding Amish is incorrect on two counts – they do vaccinate (http://www.ncbi.nlm.nih.gov/pubmed/17133167?dopt=AbstractPlus), and unfortunately, they do suffer from autism (http://scienceblogs.com/insolence/2010/05/richard_moore_swallowing_antivaccine_lie.php).

  4. Rob H said,

    Shorter Oliver Dowding:
    “Yeah well, so much for your large-scale observations and epidemiology but the Amish don’t vaccinate* and what about those 85 children in 1942?”

    * They do: http://autism.about.com/b/2008/04/23/do-the-amish-vaccinate-indeed-they-do-and-their-autism-rates-may-be-lower.htm

  5. WH said,

    What about those 85 children? Before measles vaccine was introduced, when every thing was “natural”, see the measles incidence here – http://www.iayork.com/MysteryRays/2009/09/02/measles-deaths-pre-vaccine/

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