Vaccination programmes the immune system – the body’s natural defence system – to recognise pathogens (including measles, diphtheria, mumps, whooping cough, smallpox, rubella, polio and tetanus) that invade the body and to remember them and inactivate them.
Vaccination is a miracle of modern medicine. It is estimated that, globally, immunisation prevents three million deaths annually. Despite the overwhelming evidence that vaccines are effective and safe, many people have strong reservations about vaccinating their children. These reservations are genuinely felt but based on misconceptions. The World Health Organisation has published a document answering the most common misconceptions.
Misconception 1: Anti-vaccine literature claims that, historically, with improving public hygiene and sanitation, diseases had already begun to disappear before vaccines were introduced, suggesting that vaccinations are unnecessary.
Although improved hygiene and sanitation help to reduce the incidence of disease, there is overwhelming evidence that vaccination is the key cause of the reduction of the diseases they target. Consider what happens when immunisation levels drop. The UK, Sweden and Japan cut back on immunisation against whooping cough in the 1970s because of fears about the vaccine. The effect was dramatic. Whooping cough epidemics broke out and significant numbers of children died: 38 in the UK.
Misconception 2: Most people who get disease have been vaccinated.
This is simply because most people are vaccinated. The misconception arises out of a misunderstanding of maths. Consider a population of 1,000 students, 995 of whom have been vaccinated against measles. The student body is then exposed to measles. The five unvaccinated students contract measles. A tiny percentage of vaccinated students do not respond to the vaccine and also catch the disease, let’s say seven students. Of the 12 students who contract measles, seven have been vaccinated (58 per cent), so 100 per cent of unvaccinated students contracted measles but only 0.7 per cent of the vaccinated students.
Misconception 3: Vaccines have harmful side effects that cause illnesses and even death.
The best-known example is the belief that the mumps, measles and rubella (MMR) triple vaccine can cause autism. This notion was sparked by a flawed and subsequently retracted paper in the Lancet in 1998. Numerous studies since have failed to find a link between MMR, or any other vaccine, and the likelihood of developing autism. Indeed, symptoms of autism have been detected in children well before they get MMR.
Vaccines are very safe. Although they can cause adverse side effects, most are minor and temporary, such as a sore arm or a mild fever. More serious adverse effects occur very rarely (between one per 1,000 and one per million doses). So few deaths can reasonably be attributed to vaccination, it is hard to assess the risk statistically. A child is massively more likely to be seriously injured by one of the diseases targeted by vaccines than by the vaccine.
Misconception 4: Vaccine-preventable diseases have effectively been eliminated, so there is no need to vaccinate children.
Vaccinations have reduced the vaccine-preventable diseases to very low levels in many countries, but some of these diseases remain common elsewhere. Travellers can carry disease into any country, and if the population is not protected by vaccination these diseases can quickly become epidemics.
Misconception 5: Giving a child multiple vaccinations at the same time for different diseases can overstimulate the immune system.
An antigen is any substance that stimulates the immune system to produce antibodies against it, and immunisation trains the immune system to recognise pathogens by exposing it to dead or attenuated pathogens. Children are exposed daily to many foreign antigens naturally; for example, eating introduces new bacteria into the body. The relatively few new antigens introduced by childhood vaccinations don’t represent an appreciable added burden on the immune system.
Studies have shown that the various recommended combinations of vaccines are as effective as giving the vaccines individually. The combinations offer the child earlier and more complete protection, require fewer visits to the clinic and pose no greater risk of adverse effects.
William Reville is an emeritus professor of biochemistry at UCC, http://understandingscience.ucc.ie