It’s always a good time to talk about vaccination, but with the topic back in the news thanks to the major measles outbreak in Auckland, we’re resharing Dr Jess Berentson-Shaw’s deep dive into the issue from March 2017.

A note from Spinoff Parents editor Emily Writes:

Vaccination is always something you have to think about when you’re a parent. Should you? Shouldn’t you? Lots of people have opinions and it’s confusing. I didn’t think too much about vaccination before having a child. I knew I would because it made sense to – but then I had a child with a serious health condition. Suddenly I had to advocate for him; I became vocally pro-vaccination. Late at night I would sit and cry reading mothers in Facebook groups convince each other not to vaccinate. They would say things like “Whooping cough is just a cough” and “Some kids just aren’t meant to survive, I shouldn’t have to put my child at risk for their child.”

I’d read these things and feel like I lived on another planet. A simple cold caused my son’s trachea to collapse and he ended up in emergency surgery – and they were saying whooping cough was just a cough. There is a huge group of mothers weeping over comments that say “my child’s body, my choice”. We sit in hospital wards staring at our babies and hoping and wishing someone will come along and properly explain that this is a choice not made in isolation. It’s a choice that impacts vulnerable children and adults. It’s a choice that says to all parents, but especially those of us with medically fragile children, that our children are loved and valued too and that their lives matter.

But I accept that it’s scary to give your child any kind of medical treatment. My son had so many necessary medical procedures in his first few months. It’s harrowing. To this day I hope I made the right choices with some of his care. My husband and I made our choices based on the advice of a team of doctors – we trusted them. We needed to trust them. We saw them save our son’s life, so why wouldn’t we? This post looks at the evidence without the emotion, something I often can’t do. It looks at risk too, because of course there is risk. It’s the first in a two part series on immunisation by our resident evidence-based scientist Dr Jess Berentson-Shaw, someone who can actually talk about vaccination without resorting to inaccurate scaremongering blogs. Because you need clear and factual information about immunisation – and that is what this post will give you.

Emily Writes, editor, The Spinoff Parents

Widespread immunisation helps everyone

A vaccination prevents an individual getting a disease, that much is pretty straightforward. Once a vaccination is administered the body responds to the vaccination to make the individual immune to a disease. However, widespread immunisation also has benefits. If enough people are vaccinated it eventually makes enough people immune that it eliminates a communicable disease (a disease you can catch from someone else who has the virus) in a community, a society, and eventually worldwide. Smallpox for example has been eradicated worldwide, thanks to immunisation.

This is known as “herd immunity”: when enough people are fully immunised (for most vaccines this is near 95% of the population), the risk of someone catching the disease and passing it to someone not immunised is very low. Eventually the disease cannot continue to live as it cannot find enough hosts for it to breed in, and it becomes extinct. If only we could do that with rats and possums so effectively!

A vaccination comes with risks

As I have talked about before, it is important to understand that no medical treatment is without risks. Having an ingrown toenail removed has a risk of toe amputation, having a general anaesthetic has a risk of brain damage.

But with most interventions the likelihood of the most severe side effect is much smaller than the risks associated with not doing the thing. So there are some risks when a child is immunised, for example inflammation at the site of the injection or fever. There are even smaller risks of some more serious side effects like an allergic reaction called anaphylaxis. However, such severe side effects occur much less often with the vaccine than they would if a person caught the disease itself.

The figure below compares the risks of having the MMR (Measles Mumps Rubella) vaccine vs. taking your risks with measles. If a million children had the vaccine, and another million caught the disease, then we would expect to see the numbers of complications in the table below.

What we can say with certainty is that there is NO risk whatsoever that you will get autism from a vaccine.

This creates a prisoner’s dilemma

A what?

Well as immunisation rates grow in a society (as they are currently in New Zealand), the risks of contracting a disease lessen, as do the overall risks in a population of being hospitalised or dying from that disease. So if enough other people are immunised, then it might be rational for some people to take the risk and choose not to vaccinate their child. In other words, if the chances of their child contracting the disease are low, the parents might choose to avoid the (also low) risks associated with getting the vaccination.

Example of a prisoner’s dilemma

For simplicity sake, let’s pretend a community has two undecided and unrelated parents, Andrew and Brian. They have herd immunity explained to them, alongside the risks of the vaccination for measles, the risks of contracting the disease and the risks of hospitalisation or death if their child gets the disease. Each are then asked to decide whether to vaccinate their child against measles. The risks and rewards for them are as follows:

• If Andrew and Brian both don’t vaccinate, each child has a higher risk of contracting the disease and of experiencing serious health effects of the illness, but they avoid the risk of vaccination side effects.
• If Andrew does not vaccinate but Brian does, Andrew’s child will have a lower risk of catching the disease, low risk of experiencing serious health effects of the illness and no risk of vaccination side effects. Brian’s child will have a low risk of the disease, low risk of experiencing serious health effects of the illness and some risk of vaccination side effects (and vice versa). In short, Andrew is taking a ‘free ride’, benefitting from Brian’s choice to immunise his child.
• If Andrew and Brian both vaccinated, both children will have the lowest risk (becoming no risk) of the disease and experiencing serious health effects of the illness, while both children have a risk of vaccination side effects.

Assuming Brian vaccinates his child, it might make sense for Andrew to choose not to. And this applies in the real world – in a mathematical sense the truly ‘rational’ parent (when understanding the real scientific risks; we are not talking myths here) may choose not to vaccinate, provided that enough of society has been vaccinated to provide herd immunity. However, eventually this would backfire on everyone, the rational parent included.

Why the ‘free-riders’ are hurting their kids (and others) in the long term

You can probably see the problems in this ‘rational’ but ultimately kind of selfish decision-making process, and not just for the wider community as a whole. In taking this ‘free ride’, parents who choose not to vaccinate could actually be harming their child in the longer term. As the vaccination rates decline (as more people choose not to vaccinate believing the risk to be low) the actual risks of contracting the disease then rise. So every child is now exposed to a greater level of risk, BUT especially those that are unvaccinated.

How do we know this? Because in countries with low vaccination rates, their rate of disease is at epidemic proportions. This interactive map shows where measles is at an epidemic rate worldwide – the majority of deaths from measles are in children under five. In Afghanistan, which has an immunisation rate of less than 40%, there were 6000 cases in 2012 (likely to be more due to poor reporting mechanisms).

And just in case you think this is a developing world problem, in New Zealand in 1991 our immunisation coverage rate at aged two years was less than 60% overall, and only 42% of Māori and 45% of Pacific children. In 1997 we had a large scale measles outbreak: there were 2169 cases notified, near 100 people hospitalised and seven people died; four of those who died were children who were not immunised (source: Ministry of Health Immunisation Handbook, 2014). Even now we don’t have the levels of immunisation we need for herd immunity – so any parent not vaccinating their child is rolling the dice with disease.

If an unimmunised child does come in contact with measles for example, there is a 90% chance they will get it. If they contract measles there is a 1 in 5 chance they will be hospitalised for serious complications and a 1 in 1000 chance they will die. So if increasing numbers of parents choose not to vaccinate due to a low risk of disease they are actually, ironically, increasing the risk of their child becoming seriously ill during outbreaks. What is almost worse is that they are putting some already really vulnerable kids at greater risk.

Free-riders risk making sick and vulnerable children even sicker

For children with compromised immunity, and in New Zealand this is mainly children and babies receiving chemotherapy treatment for cancer or with immune system diseases, if they contract measles they have a 1 in 2 chance of dying from it. Young babies, who have undeveloped immune systems and are too young to get a vaccination, are at high risk of contraction and hospitalisation during an outbreak of a disease. Children in poverty, who already suffer an additional disease burden compared to their better off counterparts, are more vulnerable also due to their lower vaccination rates.  So as the rate of a disease increases due to a decline in vaccination rates, the kids that suffer from this decline are those that are least able to cope.

Only a few of us can have a free-ride and it needs to be based on need

If herd immunity is achieved when 90-95% of the population are fully immunised (depending on the disease) and this rate is maintained for a period of time, then the 5-10% we can carry unimmunised in our society needs to be reserved for those with the greatest need, not those who want to opt out. It is like giving the wheelchair to someone with an ingrown toenail when there is a person with paralysis next to him or her in the queue.

It helps if information about the risks and benefits, both individual and population based, are communicated effectively and people are given the opportunity to understand that their personal decision affects everyone.

*

In summary, having your child vaccinated helps not only your child but also everyone in society. The risks from a vaccination are much lower than the serious risks that come with the diseases we vaccinate against. It might seem a good idea, to some, to get a ‘free ride’ from the lower disease rates we currently experience and not vaccinate. However, this lower rate only exists because people vaccinate their children. Ultimately such free riding will put all children who are not immunised at greater risk, as disease rates will go up again.

So be bold, be brave, be community minded and do the right the thing, for your child and others.

Dr Jessica Berentson-Shaw is a mother of two, scientist, writer, and author. This is her approach to writing about science for The Spinoff Parents.