Some people who refuse vaccinations might decide they don’t mind running a risk with their health. For example, a healthy, fit person in their 20s may decide they are unlikely to become seriously ill with Covid-19, a disease which is most serious for people over the age of 65.

However, getting vaccinated does not only involve making a choice about your own health.

Unvaccinated people are at a higher risk of passing an infectious disease to others who, for medical reasons, cannot get vaccinated. 

Children undergoing treatment for leukaemia must delay getting the measles, mumps and rubella (MMR) vaccine, for example. That puts them at risk of contracting measles, a highly infectious disease, if they are near anyone who has it. They are also at a greater risk of suffering complications of measles. 

Irish statistics on vaccine uptake and Irish research on vaccine hesitancy, which is when someone is reluctant to get a vaccine, tell a similar story: the vast majority of people in Ireland trust and accept vaccinations.

The most recent data shows that between 80% and 92% of children under 2 receive each of the vaccines offered routinely to all babies in Ireland. By September 2021, during the Covid-19 pandemic, less than 10% of people over the age of 16 in Ireland remained unvaccinated.

A minority of people do not receive vaccines they are offered.

Sometimes that’s simply because appointments get missed or because a person is not registered with a GP and falls through the health system’s cracks.

Sometimes it’s because of people’s concerns about vaccines.

Vaccines have been around for over 200 years - and so have fears about their safety.

The first modern vaccine, that against smallpox, was developed in 1796. It was based on the related but milder disease cowpox, injected into people in the form of calf lymph. 

Smallpox inoculation became compulsory for children in Britain in the 1850s, and in Ireland in the 1860s. 

These programmes were resisted by some, including on the grounds that animal matter was being injected into children - as satirised in this early cartoon depicting cows sprouting from vaccinating people by English caricaturist James Gilray in 1802.

Conspiracy theories circulated, alleging that deaths from vaccines were being covered up by the medical profession and that the vaccines caused harm to children such as “mania” and syphilis. Some parents objected on conscientious grounds to being forced to vaccinate their children.

These two boys, both aged 13, were in the same class in school and exposed to the same smallpox source on the same day. The boy on the right had been vaccinated and the boy on the left had not because his parents refused, having become caught up in anti-vaccine fervour in their local area. 

The photograph, taken in Leicester Isolation Hospital, was published in a medical journal in 1901.

Before the introduction of vaccination, smallpox was one of the deadliest diseases known to humans. It killed one in three people infected, and left many others with permanent after-effects including scarring, blindness and infertility.

The last recorded death from smallpox in Ireland occurred in 1907, less than 50 years after childhood vaccination was introduced here. By 1980 the disease had been eradicated worldwide.

Today, fears about side effects, and a perception that the risks of vaccines do not outweigh the benefits, are the main reasons people decline immunisations for their children, according to recent research.

Dr Chantal Migone is a specialist in public health medicine at the National Immunisation Office, part of the HSE. She says it is “important to acknowledge these concerns and to address them with accurate information”.

“We would always encourage people to look for information about vaccines from reputable organisations, like our own Immunisation.ie website, which is accredited by the World Health Organization (WHO), and the WHO website itself.

“Unfortunately, there is misleading information out there that can really cause some people to worry, and we don’t want people to make a decision about vaccination based on incorrect or misleading information.”

Pathogens are organisms - such as bacteria or viruses - that can cause disease. Our bodies react to pathogens by producing antibodies to fight against disease.

The first time the human body is exposed to a pathogen, it takes time for the immune system to respond and produce the right antibodies to fight that antigen. If the body is exposed to the same pathogen again, the antibody response is much faster and more effective. 

That is why, for example, most children get chicken pox - which is highly infectious - once, but it is very unusual to get it twice.

Vaccines contain weakened or inactive parts of the bacteria and viruses that cause disease, or tiny fragments of them such as a particular protein or sugar. Because vaccines are based on weakened or inactive versions of these organisms, or on tiny fragments, getting vaccinated cannot give you the disease. 

For example, being injected with the vaccine against whooping cough cannot give a person whooping cough. However, the vaccinated person’s immune system is now primed to respond quickly and effectively if they are ever exposed to the bacteria, Bordetella pertussis, that causes this disease.

That means if an infected person coughs or sneezes near a vaccinated person, the vaccinated person’s immune system is able to protect them against falling sick with whooping cough too.

• For more information, there is an article on how vaccines work on the World Health Organization website.

Dr Migone says people who feel hesitant about a vaccine may be reassured by learning about how the approval process for vaccines works and the several layers of checks and balances that exist.

The part of the vaccine that generates an immune system response in the vaccinated person is caused by the “antigen”, or active ingredient.

Vaccines are usually developed by private companies, often in collaboration with universities or research institutes. This initial phase of development involves laboratory tests to figure out which antigen should be used to generate an immune response.

Once researchers think they have a vaccine they move on to testing it on animals, to check it works and to evaluate its safety.

If the vaccine triggers an immune system response and there are reasonable grounds to believe it is safe, human clinical trials begin. At first, the vaccine will be tested only on a small number of volunteers - usually young, healthy adults - to assess its safety, confirm it generates an immune response and determine the right dosage.

A second phase of human trials involves testing on hundreds of volunteers to assess how it works on different age groups and to examine different formulations of the vaccine - with a particular focus on people who have the same characteristics (age, sex etc.) as the people for whom the vaccine is intended.

A third phase involves even more extensive testing, this time on volunteers, usually across multiple countries to check the findings across many different populations. Each expanding phase of clinical trials allows scientists to gather data on side effects and risks.

• The World Health Organization and the Centres for Disease and Control and Prevention in the US have both produced articles on how vaccine trials work.

When the results of all these clinical trials are available, regulators in many different countries assess the data.

“All vaccines that we use in our Irish immunisation programme have been rigorously tested,” Dr Migone said.

“They go through regulatory approval by the European Medicines Agency first, and then, when they receive regulatory approval, they have to be recommended by the National Immunisation Advisory Committee (NIAC).

“That is a group of experts that includes doctors, paediatricians, scientists, GPs, public health nurses, and representation from members of the public.

“It’s only once they have been recommended by NIAC that vaccines can be used in our national immunisation programmes in Ireland.”

Some of the diseases against which vaccinations are routinely offered in Ireland are extremely serious - and not getting vaccinated puts an unvaccinated person at a higher risk of catching them.

Meningitis is one example of a serious, vaccine-preventable disease. 

One in 20 people who contract meningococcal disease - more commonly known as meningitis - will die. One in 10 survivors will be left with a major disability such as deafness, brain damage or amputations. 

Since the year 2000, when routine vaccination of babies against menC was introduced in Ireland, there has been a dramatic decline in the incidence of infection, from 139 cases in 2000 to fewer than 10 in 2021.

Lauren Sandell from London was 18 and had just started university when she died from sepsis caused by meningitis type W infection in 2016.

Before Lauren left for university, her mother, Sharon, tried to arrange for her to receive the then newly available MenACWY vaccine, which provides immunity against the A, C, W and Y strains of meningococcal disease. However, the GP’s surgery did not have a dose available.

Two weeks after she left for college, Lauren travelled home for the weekend. She was already feeling ill, putting it down to stress and possible food poisoning, and she became increasingly unwell.

“She didn’t look great. She said her legs hurt. But she was planning to go out that night with friends,” Sharon said.

Lauren had a bath and went to bed. The next morning - Sunday - she couldn’t stop shaking and she began to struggle to breathe. Sharon and her son took turns performing CPR on Lauren as they waited for an ambulance to arrive, but when the paramedics reached them minutes later, Lauren had died.

“Lauren would be here today if she’d had that jab, if they’d had one for her that day. There is no doubt about that,” Sharon said.

Lauren’s opportunity to be vaccinated was missed through a number of sliding doors. Her school offered the vaccine to some year groups but unfortunately not to hers.

Sharon said that people who feel dubious about vaccines must weigh up the consequences of the diseases vaccines prevent. The particularly deadly meningitis W and sepsis that Lauren became infected with took her life very quickly and was not accompanied by the classic symptoms of meningitis people might expect, such as a rash. 

“When there was a scare with the MMR [measles, mumps and rubella] vaccine, I decided I would read for and against and get as informed as I could. That is what I did and I made the decision that prevention is better than cure.

“I know people are scared of jabs, but you’ve got to be scared of diseases - like measles, which is coming back now. I don’t think it’s easy for any parent, but there is that responsibility,” Sharon said.

In Ireland, the MenACWY vaccine is now offered in the first year of secondary school.

• Extensive information on meningitis, its symptoms and on vaccines against the disease is available on the website of the British and Irish Meningitis Research Foundation. In the last school year, uptake stood at just over 80%.

Some women who trust vaccines in general may feel hesitant about getting vaccinated when they are pregnant. Here too there is a track record of vaccination over many years to look back on.

In Ireland, it is recommended that babies are vaccinated against whooping cough at 2, 4 and 6 months to build up their immunity to this life-threatening disease. 

The HSE says many babies who fall ill with whooping cough are hospitalised with complications such as pneumonia and brain damage. The disease can last up to three months. It is most serious in babies under six months.

Women in Ireland are offered a vaccination against whooping cough in pregnancy. The vaccine stimulates their immune system to produce antibodies to the whooping cough bacteria which pass to the baby in the womb and protects them in the first few months of life, before they are fully vaccinated themselves.

This vaccine has been recommended for pregnant women in Ireland for the past 10 years.

Similarly, the flu vaccine has been administered to pregnant women in Ireland for over a decade - and for over 50 years in the US. Because the vaccine is based on inactivated virus material it is not possible to contract the flu from this vaccine - or for an unborn baby to get sick either.

Sometimes a vaccine becomes associated with a particular side effect, perhaps as a result of correlation being confused with causation. 

One such association was the idea that the MMR vaccine caused autism. The man who made this completely false claim in 1998 was struck off as a doctor, and extensive research - including one study looking at every child vaccinated in Denmark over eight years - has demonstrated that there is no link between the MMR vaccine and autism.

Claims that the HPV vaccine - which provides protection against a virus that causes cervical cancer and other cancers - causes chronic fatigue have also been shown to be incorrect by several major scientific studies. Links to several such studies can be found here. 

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There is no known cause of either autism or chronic fatigue syndrome. The signs of autism normally develop around the time children receive their first MMR vaccine, while chronic fatigue syndrome is more common with girls and can develop in puberty - which is also when the HPV vaccine is administered.

In both instances, this correlation in timing may have led families searching for answers about their children’s conditions to draw a mistaken link with vaccination.

There has been one case in recent decades of a vaccine causing a serious side effect. The Centers for Disease Control and Prevention (CDC), the national public health agency in the US, explains on its website that an increased risk of narcolepsy was found in a number of European countries following vaccination with Pandemrix, a 2009 vaccine used during the H1N1 flu pandemic.

This vaccine has not been used in Ireland since 2011. 

Scientists have not yet drawn a firm conclusion on the mechanism by which Pandemrix was associated with narcolepsy, a condition that makes people very drowsy. Possible explanations, including that a combination of the vaccine with prior infection with the H1N1 virus could have triggered narcolepsy in people with a genetically predisposition to the condition, are set out in this article by the Institute for Vaccine Safety at John Hopkins University in the US.

Irish research has indicated that people are more likely to be vaccine hesitant if they have lower trust in official sources of information.

Dr Migone recommends that anyone who is unsure about a vaccine, even after reading about it - for example in the parents’ guide to childhood immunisations distributed by the HSE - should talk to someone in person. 

Their GP, their practice nurse or their public health nurse will be able to answer specific questions they may have. 

“Don’t be afraid to ask questions,” Dr Migone said. 

“But get the information from a reputable source, such as your doctor, nurse or pharmacist - they’ve had the training and they have the experience.”

Dr Luke O’Neill, an immunologist at Trinity College Dublin was often on the airwaves during the Covid-19 pandemic, explaining the virus and the scientific race to control it, particularly using vaccination. 

He points out that ultimately, making a decision about vaccination comes down to weighing up the risks and benefits. For all vaccines currently offered routinely in Ireland, there is no question that the benefits vastly outweigh any risks. 

O’Neill said he would say to anyone unsure about whether to accept a vaccine either for themselves or for their child: “I understand your concerns and your reservations, because it's understandable that you would have concerns.

“And then you say, ‘Well, look, all the evidence is strongly in favour of vaccination, because the benefits far outweigh the risks. There are risks. Every medicine comes with a risk, even aspirin. 

“But the fact is, given that these vaccines have been in millions of people, that they've been carefully tested, the benefits far outweigh the risks. There's more risk to your child being harmed by an infection than by the vaccine,” he said.

Migone too believes some people may not be vaccinated because they don’t think about or are not aware of the risks of vaccine preventable diseases.

She gives the example of the HPV vaccine offered to teenage girls to protect against the virus that causes cervical cancer. A significant disinformation campaign in Ireland against the vaccine a decade ago, falsely alleging harmful effects to vaccinated girls, saw uptake drop as low as 50%.

Twenty-five-year-old Laura Brennan contacted the HSE in 2017, three days after being told that the cervical cancer she had been diagnosed with six months before was metastatic and incurable. Brennan was too old to have received the vaccine, which was introduced in Ireland in 2010.

She became the face of a major HSE communications campaign to convince parents and teenagers of the facts about the vaccine, using her own story to bring home to people the reality that being unvaccinated meant risking a cancer diagnosis like hers in the future. Within a year, uptake had risen to 65% and the most recent figures were above 80%.

“Laura sharing her story was really powerful and undoubtedly made a huge difference,” Migone says.

Speaking on RTÉ’s Late Late Show in April 2018, a year before she died, Brennan said she would tell any parent unsure about vaccinating their children: “It’s natural to be scared of things.

“I probably would have been scared if I didn’t have the full information.

“I would urge parents to go onto reputable websites….If there’s something they’re not sure about, go to their GP. At the end of the day this is a medical issue.”