Once upon a time the release of a vaccine was a cause for widespread celebration. Within four years of introducing the measles vaccine in 1964 the number of cases in the US dropped from more than 400,000 per year to about 10,000. At its peak in the US more than 3,000 people died in a single year from paralytic poliomyelitis, more than from any other communicable disease. Three years later, Jonas Salk introduced a polio vaccine that was used for a mass vaccination programme and ultimately led to the complete eradication of the disease in all but a handful of countries. Contemporary reports talked of the palpable relief and joy at the news of the vaccine. The day following the announcement the New York Times ran a headline, "Salk receives thanks of nation".
When someone gets an infection, a healthy immune system will mount a response which involves making antibodies that recognise the disease-causing infectious agent (or "pathogen") and target it for destruction. The antibodies match the pathogen in a lock-and-key type relationship that is highly specific. This response usually takes several days to come into effect, and longer if someone is weakened by the infection.
For serious infections such as polio and measles this is too long and allows time for the infection to cause long-term health problems or death. However, once the antibodies have been produced the first time, the immune system of survivors retains the ability to rapidly synthesise them at a future date. It is this capacity for a rapid response that confers immunity, and it may endure several years or a lifetime.
Vaccines work by stimulating this “memory formation” in our immune system without causing the disease. This is done by introducing a lookalike of the pathogen in question that will trigger antibody production. Vaccines don’t take hold in everybody but if a large enough proportion of the population is vaccinated then everyone is protected because the virus will be unable to gain a foothold in the population. This is usually called “herd immunity” and often requires over 95 per cent of the population to be vaccinated.
However, in recent years people have become fearful of vaccines and complacent about the diseases they are preventing. The US declared measles eliminated in 2000 but is currently experiencing an outbreak which has so far affected 173 people. Germany too is experiencing an outbreak of measles with over 400 cases in the last few months.
I once heard a professional Irish politician from a small party dismiss measles vaccination programmes with the opinion that it is better to have the disease than the vaccine. She based this claim on her personal experience of seeing many classmates when she was a child get measles and make full recoveries. This is good news for those individuals, but it doesn't change the fact that measles is one of the leading causes of deaths among children globally. The WHO reports that in 2013 there were 145,700 deaths from measles worldwide. They also estimate that during the period 2000-2013 vaccination programmes prevented 15.6 million deaths from measles.
A large number of people are actively choosing not to get their children vaccinated. This places at risk those who cannot take the vaccine due to underlying medical conditions as well as infants who have not yet received the vaccine. A large contributor to this poor vaccine uptake is the unfounded fear that the vaccines cause developmental disorders such as autism. This itself is largely due to a false and fraudulent study that was published in the Lancet in 1998. The doctor responsible for this report was disbarred and the paper was retracted by the journal, yet it seems the notion has stuck and a huge amount of damage has been done.
In areas currently experiencing the Ebola outbreak all other medical interventions have been drastically disrupted, including childhood vaccination programmes. In a paper published this month in the journal Science, it was estimated that there will be an additional 16,000 measles deaths in Guinea, Liberia and Sierra Leone due to the interruption of the vaccination programme.
Safe, effective vaccines are one of the most important discoveries of modern medicine. We are lucky to have free access to childhood vaccination programmes and they should not be passed over lightly.
Aoife McLysaght is a professor in Genetics in Trinity College Dublin where she leads a research group focusing on identifying and interpreting the evolutionary patterns in animal genomes