The worrying increase of vaccine hesitancy

Why do many people prefer to believe scary misinformation on social media over science-backed statements from health experts?

Recent surveys show that people are becoming increasingly sceptical of vaccination despite the history of vaccination programmess in eradicating/controlling a host of killer diseases, including the current spectacular worldwide success of Covid-19 vaccines.

Many people prefer to believe scary misinformation spread on social media in preference to the reassuring science-based pronouncements made by professional health organisations. This is a most dangerous situation.

Our bodies are naturally equipped with a system to protect us against invading pathogenic agents, eg certain bacteria and viruses. This immune system can be artificially tuned/boosted to increase our levels of protection against toxic agents. This is done by introducing a weakened or killed form of the pathogen into the body – vaccination.

The modified agent introduced does not induce disease in the host but confers acquired immunity so that, if the body later encounters the active disease-causing agent, the immune system is ready to mount an immediate defence.


The English physician/scientist Edward Jenner (1749-1823) pioneered the concept of vaccines and created the world’s first vaccine, the smallpox vaccine. Jenner’s work is said “to have saved more lives than any other man”. In Jenner’s time deadly smallpox killed about 10 per cent of world population, and up to 20 per cent in towns/cities where infection spread quickly. Smallpox was eradicated globally in 1977 thanks to vaccinations.

We now have vaccines to prevent more than 20 life-threatening diseases (including chickenpox, diphtheria, flu, hepatitis, human papilloma virus, measles, meningococcal, mumps, pneumococcal, polio, rotavirus, rubella, tetanus, whooping cough). The World Health Organisation estimates that immunisation currently prevents five million deaths per year globally, almost certainly an underestimation. Global vaccination rates are improving but vaccination coverage is lowest in the poorest countries. For example, although rotavirus is a leading cause of childhood mortality from diarrhoea; only 35 per cent of children globally get a rotavirus vaccine.

Sixteen per cent of Americans believe ‘increased vaccinations are why so many kids have autism these days’

Thankfully, we have now come through the horrible Covid-19 pandemic, thanks largely to the development and global deployment of new Covid-19 vaccines. A recent study (Oliver Watson and others, Lancet Infectious Diseases, September 2022) estimates that Covid vaccines prevented 19.8 million deaths globally during the first year after vaccine campaigns were initiated.

The general public is growing more suspicious of vaccination programmes. A Wellcome Global Monitor, Gallup World Poll 2018 found that only 50 per cent people in eastern Europe, 72 per cent in North America and northern Europe, and 76 per cent people in southern Europe believe that vaccines are safe.

And this pattern continues despite the amazing success of the Covid-19 vaccines. The Annenberg Public Policy Centre, University of Pennsylvania, carried out a survey in October 2023 and found that public confidence in vaccinations is dropping steadily: the percentage of adults who believe that approved vaccines are unsafe rose to 16 per cent from 9 per cent in 2021. The survey also found that false and unproven claims about vaccines and Covid-19 are more widely accepted today than 2½ years ago, despite intense efforts to counter misinformation.

Sixteen per cent of Americans believe “increased vaccinations are why so many kids have autism these days“. There is a growing belief in the false MMR-autism link, which has been debunked over and over again, with 12 per cent now believing it to be true, up from 9 per cent in 2021. Twelve per cent of people think mRNA Covid-19 vaccines cause cancer, up from 9 per cent in January 2023, although there is no evidence these vaccines cause or accelerate cancer. And 21 per cent of people think it is safer to get Covid-19 than to take the Covid-19 vaccine!

The anti-vaccine movement spreads misinformation and silly conspiracy theories on social media. One conspiracy theory claims that powerful people created the Covid-19 virus to stimulate a massive global immunisation response through which microchips would be injected into people allowing a global surveillance network to be established!

Individual decisions not to accept vaccination have negative consequences elsewhere in the population. The greater the proportion of people in the community who are vaccinated, the better protected everyone is because disease transmission is greatly reduced or stopped – herd immunity.

This is very important for those who cannot be vaccinated, eg immune-compromised children. The fact that vaccination is so successful, saving so many lives and eliminating so much human misery, but is yet unacceptable to a significant fraction of the population is, to say the least, worrying.

William Reville is an emeritus professor of biochemistry at UCC