A recent measles outbreak in Ottawa has led many people to revisit the ‘vaccine debate,’ with many opinions grounded in science fiction instead of science. Let’s look at the facts.
The development of safe, effective vaccines is one of the most important advances of the twentieth century. Before vaccines, childhood infectious diseases such as measles, polio, and rubella were commonplace. Vaccination means that many of these diseases are now preventable and extremely rare. Vaccination allowed us to eradicate smallpox in 1979, and a similar campaign is coming close to achieving the same for polio. On March 27, 2014, The World Health Organization (WHO) declared South-East Asia to be polio-free and estimates that the world is now 80% polio-free (http://www.searo.who.int/mediacentre/releases/2014/pr1569/en/). This achievement can be credited to vaccination and improvements in hygiene and sanitation.
Vaccination for public health operates on the basis of herd immunity. Herd immunity works by protecting unvaccinated individuals when a critical proportion of the population has been vaccinated. This means that we can eliminate a disease with less than 100% vaccine coverage in a specific population. Herd immunity is important to protect those individuals who cannot be vaccinated, for example the immunosuppressed and very young infants.
Vaccines have been studied extensively, and determined to be safer than many modern therapeutic medicines (http://www.who.int/bulletin/volumes/86/2/07-040089/en/). However, a study conducted in 1998 proposed a link between autism and thimerosal, a preservative sometimes used in vaccines. This study has since been retracted due to flawed methodology, and many follow-up investigations have been done – all available evidence suggests no link between vaccines and autism. Unfortunately, the initial study caused panic and reduced childhood vaccination rates in some countries.
Sometimes people will say that they knew of a toddler who was developing normally, then was diagnosed with autism after being vaccinated. While a cardinal truth in all sciences is that correlation does not equal causation, these spurious observations are actually examples of specious reasoning. Many important life events tend to happen around the same time: first words, first vaccination, first significant exposure to solid foods, and for a few, diagnosis with certain conditions, including autism. We must be careful not to associate undesired circumstances with unrelated exposures simply because of chronological convenience. Vaccinations are an easy target for blame, since they seem unnatural.
Adverse reactions to vaccines do occur. These normally involve swelling, redness, and pain at the injection site. More severe reactions include anaphylaxis and the development of Guillain-Barre Syndrome, which is extremely rare. However, it has been determined that an individual’s risk of developing complications from a vaccine-preventable disease is higher than their risk of experiencing a serious vaccine-related adverse effect.
|Vaccines cause autism||All available evidence does not suggest a causal relationship between vaccines and autism|
|Vaccine-preventable disease are just an annoyance, and are not very severe||Illnesses such as measles, mumps and rubella are serious and can lead to severe complications in both children and adults, including pneumonia, encephalitis, blindness, diarrhea, ear infections, congenital rubella syndrome, and death|
|It is better to gain immunity through disease than through vaccines||Vaccines interact with the immune system to produce an immune response similar to that produced by the natural infection, but they do not cause the disease or put the immunized person at risk of its potential complications.|
|Better hygiene and sanitation will make diseases disappear – vaccines are not necessary||The diseases we can vaccinate against will return if we stop vaccination programs. While better hygiene, hand washing and clean water help protect people from infectious diseases, many infections can spread regardless of how clean we are.|
|Vaccines contain mercury which is dangerous||Thimerosal is an organic, mercury-containing compound added to some vaccines as a preservative. There is no evidence to suggest that the amount of thimerosal used in vaccines poses a health risk.|
The ongoing measles outbreak in Ottawa illustrates the consequences of reduced vaccination coverage for this disease. Once a common childhood illness, today measles is rare in Canada due to adequate immunization coverage. Measles causes fever, dry cough and runny nose, and a skin rash. Complications include ear infection, pneumonia, and encephalitis. Approximately three out of every 1000 measles patients in Canada die. Measles is highly infectious. It is spread by infected water droplets and is facilitated by person-to-person contact.
The first case in the measles outbreak in Ottawa was an unvaccinated child who contracted the virus in the Philippines. The child was infectious when he returned to school, exposing many other children, including 12 who were not vaccinated. These 12 students were told to stay home until March 26 in an effort to contain the spread of the disease. One of the original case’s classmates contracted the disease from him – it is unclear whether or not this child was vaccinated.
Children attending school in Ontario must be up-to-date on their vaccines (http://ottawa.ca/en/residents/public-health/disease-and-medical-conditions/immunization-requirements-school-registration). Public Health units collect vaccination record information upon school registration and review it annually to ensure that students are in compliance with vaccination schedules. However, if parents do not vaccinate their child due to medical, religious, or philosophical reasons they may be eligible for an exemption. This is likely how the initial cases in the measles outbreak in Ottawa entered school.
As of April 7, 2014, two additional cases of measles have been detected – one in an immunized adult and one in an unimmunized child. One dose of the measles vaccine is effective in about 95% of people; a second dose protects almost all. The immunized adult with measles was therefore probably in the small fraction of people for which the vaccine does not work. Ottawa Public Health has issued a public service announcement warning people of when and where they may have been exposed to it (http://ottawa.ca/en/news/two-additional-cases-measles-confirmed-ottawa). Given the infectiousness of measles, I would expect several more cases before this outbreak is contained.
So what is the lesson here? While it is important to be aware of potential threats to our children, we should also be diligent in turning to true experts and authorities for a proper assessment of the evidence and threat level, and not rely on questionable blogs and celebrity spokespeople. The best science strongly suggests that almost all children (with a handful of exceptions) should be vaccinated against ancient killers like Measles. Failure to do so may put the entire community at risk.
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