What happens when vaccination rates fall

Image via the CDCThis year is shaping up to be a challenging one for measles control. Once considered eradicated in North America, it’s seen a bit of a resurgence in the States, almost entirely among the unvaccinated. From the Public Health Agency of Canada:

Measles cases are rising dramatically in France, Germany, Belgium, Romania, UK and even in some parts of the USA. Californian health authorities say that non-immunized Californians are becoming infected after travelling abroad and infected foreigners travelling from abroad into California are infecting local people. The World Health Organization, which thought the world was close to eliminating measles, has postponed the date for that target to 2015 – which most experts believe is far too early.

Where is it spreading? Almost entirely amongh the unvaccinated. CDC noted this week:

Of the 118 cases, 47 (40%) resulted in hospitalization. Nine patients had pneumonia, but none had encephalitis and none died. All but one hospitalized patient were unvaccinated. The vaccinated patient reported having received 1 dose of measles-containing vaccine and was hospitalized for observation only. Hospitalization rates were highest among infants and children aged <5 years (52%), but rates also were high among children and adults aged ≥5 years (33%).

Unvaccinated persons accounted for 105 (89%) of the 118 cases. Among the 45 U.S. residents aged 12 months−19 years who acquired measles, 39 (87%) were unvaccinated, including 24 whose parents claimed a religious or personal exemption and eight who missed opportunities for vaccination. Among the 42 U.S. residents aged ≥20 years who acquired measles, 35 (83%) were unvaccinated, including six who declined vaccination because of philosophical objections to vaccination. Of the 33 U.S. residents who were vaccine-eligible and had traveled abroad, 30 were unvaccinated and one had received only 1 of the 2 recommended doses.

Nine outbreaks accounted for 58 (49%) of the 118 cases. The median outbreak size was four cases (range: 3–21). In six outbreaks, the index case acquired measles abroad; the source of the other three outbreaks could not be determined. Transmission occurred in households, child care centers, shelters, schools, emergency departments, and at a large community event. The largest outbreak occurred among 21 persons in a Minnesota population in which many children were unvaccinated because of parental concerns about the safety of measles, mumps, and rubella (MMR) vaccine. That outbreak resulted in exposure to many persons and infection of at least seven infants too young to receive MMR vaccine.

I wasn’t able to find any incidence rates for Canada for 2011, other than this bulletin from the Chief Public Health Officer in Nova Scotia who notes:

For 2011, Quebec has seen the highest number of measles cases in Canada, and currently have 17 confirmed and probable cases. Travel to Europe, particularly France, was associated with 6 of the cases. There have also been confirmed cases in Saskatchewan and BC. There have been no reported cases in N.S. since 2008.

So it looks like the situation is not nearly as bad in Canada. (If anyone can find current Canadian stats, please share the link.) And pity the poor British, who are experiencing an outbreak of measles much larger than the Americans. And it’s no surprise – MMR vaccination rates in some regions are shameful – as low as 32%.

MMR is administered in two doses – one at about one year old and the second batch just before going to school. The chances of a child getting both are less than 100%: across England, around 78% of children have received both jabs by their fifth birthday.

  • Brent, in London, has the lowest immunisation rates for MMR – only 32% of children have had both jabs by their fifth birthday
  • It’s followed by other London boroughs too: Hackney, Haringey and Barking
  • In contrast, in Barnsley, Yorkshire, 91.5% of five-year-olds have had both jabs – the highest figure in England

It’s even worse in France – over 7500 cases, so far in 2011.

I have written repeatedly about the merits of vaccination and the public health dangers of the antivaccination movement, which questions the safety and efficacy of vaccines. This week’s edition of the journal Nature has some interesting articles on vaccines. I recommend Vaccines: The case of measles, Target the fence-sitters (on antivaccination sentiment) and a great article, The real issues in vaccine safety.  Antivaccine sentiment is nothing new, particularly among alternative medicine providers. For a historical perspective, check out this recent Science-Based Medicine post where Kimball Atwood looks at the roots of the antivaccination movement, and the rejection of the smallpox vaccine by homeopaths and naturopaths.

Canada may be virtually free of measles today, but the unvaccinated are at risk as long as it exists worldwide.  Questions about the MMR vaccine, or other vaccines? Excellent Canadian data are available in the Canadian Immunization Guide.

2 thoughts on “What happens when vaccination rates fall

  1. The 7 infant cases cited in Minnesota are precisely the reason we need high vaccine uptake throughout the population. Their immune systems are too immature for the vaccine to be effective, and they are at the greatest risk of severe morbidity from the disease itself.

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