The sudden death of a leading scientist following a routine inoculation for yellow fever has reignited one of the biggest controversies in medicine - just how safe are vaccines?
Professor Martin Gore of the Institute of Cancer Research in London, suffered total organ failure shortly after receiving the dosage, and died last week.
While his death is still under investigation, attention has focused on the vaccine as the most likely cause.
The incident has reopened a perennial debate on whether the benefits of vaccines outweigh the potential risks, and offered fresh insight into how the public can be swayed by raw emotion and mass media outrage over scientific fact.
It is believed Prof Gore, 67, had the vaccination prior to travelling to a region where yellow fever is endemic. A lethal mosquito-borne disease, it is common in tropical regions of Africa and Central and South America, and kills up to 50 per cent of those who develop the full-blown disease.
But since the 1930s, a vaccine has been available which offers life-long protection from a single shot. Containing a weakened version of the virus, it allows the body’s immune system to build defences against infection.
Over the decades, the dose has protected hundreds of millions of people from the deadly disease.
Like every vaccine, however, the protection is not without risks. It causes mild side effects like headaches and a fever in around one to three of those who receive the vaccine. But in around one in 250,000 cases, it triggers symptoms very similar to yellow fever itself, including kidney and liver failure, leading to the jaundice that gives the disease its name.
These risks are substantially high for those over the age of 60 – such as Prof Gore.
Despite being deemed more than 1,000 times lower than the risk of dying from the disease itself, some experts believe they are enough to justify simply avoiding travelling to infected countries.
Whether Prof Gore was aware of this fact is not known. What is clear is that for many people, vaccination involves making decisions that are based on more than just numbers.
Attitudes towards the risks involved can be dictated by subjective concerns that scientists themselves often underestimate.
One key concern is the effect from media coverage, and the fact that even rare events will eventually occur at times.
This has profound implications for public health measures such as vaccinations, which routinely involve millions of people.
And when rare events do occur, they often garner media coverage precisely because they are linked to something familiar to many of us.
In 2008, many countries – including the UAE – began offering young women vaccinations against HPV, the virus responsible for cervical cancer. Within months, the UK media reported the tragic case of a teenage girl, 14, who had died within hours of receiving the vaccine.
The coverage prompted calls for the programme to be abandoned. By that time, more than a million girls had been given the vaccine in the UK – making it likely that even a rare condition would have led to a tragic outcome.
In the event, doctors discovered that the girl had, in fact, succumbed to an undiagnosed malignant tumour – making her death a tragic coincidence unrelated to the vaccine itself.
Yet the coverage sparked public concern that likely deterred many from getting the proven protection offered by the vaccine, judging the risks to be too high.
Scientists stress, however, that risk assessments cannot be based on anecdotes, and must always be put in context.
But evidence suggests many people find anecdotes more compelling than numbers.
During his campaign for the US presidency, Donald Trump repeatedly claimed that a vaccine given to children to protect against mumps, measles and rubella (MMR) was linked to cases of autism. First proposed by a now discredited researcher in 1998, no such link has been found by other researchers in studies that covered more than 15 million children worldwide.
Mr Trump’s claims became the focus of a US Republican primary TV debate in 2015. Rival candidate Dr Ben Carson – a retired neurosurgeon – insisted that many studies had failed to find “any correlation between vaccinations and autism”.
But in response, Mr Trump told a story of how a child of someone he knew was given the vaccine, and a week later “got a tremendous fever, got very, very sick, and now is autistic”.
Even scientists conversant with the facts have conceded to finding Mr Trump’s personal anecdote more immediately compelling than Dr Carson’s facts.
According to some researchers, this reflects the fact that humans have spent far longer understanding the world through stories than through data.
Until we do, the best advice is perhaps to follow the scientific maxim that the plural of anecdote is not data.
Robert Matthews is Visiting Professor of Science at Aston University, Birmingham.