We at UYBFS like a good joke. In that spirit, we posted a cartoon poking fun at Jenny McCarthy, D-list actress and notable anti-vaccine advocate, to a Facebook page called Science Humor. It’s a funny page, if you’re in to science puns and jokes you need an advanced degree to understand, which we totally are.

People liked the cartoon, but we were very surprised by a vocal minority of people who responded to the post with very vehement anti-vaccine views. Our surprise stems from the fact that the name of the page is “Science Humor”, which we assumed would narrow down the active readers to people with a strong background in science, of which we know exactly zero who oppose the use of vaccines or believe (as Jenny McCarthy does) that vaccines cause autism.

Our assumptions were wrong. Some of the anti-vaccine supporters clearly had some background in science. They posted articles supporting their views and seemed to be looking for debate. Meanwhile, some of those who took the pro-vaccine side just resorted to name calling rather than engage in scientific debate. (In all fairness, there was name calling on both sides).

We stayed out of the debate. In part, we wanted to see where the discussion went, but mainly, we are of the mind that the comments section in a Facebook post is not a good place hold detailed scientific discussions. However, we need to acknowledge that there are people out there with very strong anti-vaccine views . Making fun of them or dismissing them as “nuts” is not productive. Our goal should be to educate, to bring them along and lay out the facts. We won’t convince those who are not open to impartially weighing the scientific evidence, but if we do our job right, we may just change a few minds for the better.

But how? Some of these people were VERY passionate about their anti-vaccine posts – can we actually change their minds? Should we go point-by-point, refuting each reference they posted? This last approach would be the most thorough, but it would also be BORING, and we actually want people to read this blog. So instead, we will focus on the major pillars of “evidence” used to support anti-vaccine views. For those aligned with science, think of this as a guide for speaking to others with opposing views. For those who hold anti-vaccine views, we hope this may bring some clarity to the science behind vaccine safety. There is a lot to unpack here, so this we’ll break our discussion into 3 parts. When possible, we’ll use some examples from the Facebook page thread, with all names redacted.

PART I: What does “safety” mean when we talk about vaccines and drugs?

Before we go any further, we need to start here. What does “safe” mean when it comes to vaccines, or anything for that matter? To most people, it means that no harm will come to them (or their loved ones) if they engage in a particular activity, like getting vaccinated, or driving a car or washing their hair. However, this is completely wrong.

Vaccines, like all drugs, are not approved because they “safe”, nor or they approved because they “work.” These are not meaningful scientific terms. Drugs are approved (in the United States and all other countries) because they have a positive benefit/risk ratio. This is because all drugs pose some degree of risk – everything is toxic if you take enough of it. This isn’t unique to drugs either – everything you do has risk. Getting in a car and driving to work is risky – usually much more risky than taking a drug to treat disease.

Risk-benefit is important because some diseases are worse than others. Patients with a life-threatening disease like cancer are willing to tolerate more side effects – even potentially deadly ones – than someone with a runny nose. This is taken into account when a drug is approved – you can tolerate a moderate risk of liver failure when treating stage IV cancer, or a small risk of developing cancer when treating serious rheumatoid arthritis, but for a cold medicine, these side effects won’t fly.

Deaths related to vaccines are very rare. So rare, that it’s really not clear how many occur per year. Children can die from a number of causes during early childhood, and it is often very difficult to assign a cause. When scientists have tried to study deaths related to vaccines specifically, they did not find an increased rate of deaths compared to unvaccinated children. These studies are confounded by that fact that vaccines save lives by preventing disease. Certainly there have been documented cases of children dying after being vaccinated, but these cases are extremely rare, and the relationship of the deaths to the vaccine is almost always unclear.

This isn’t to say that vaccines have no side effects. They certainly do. The ones that we are most concerned with anaphylaxis, allergic reactions, and febrile seizures, which are seizures brought on by a high fever which may be caused by the vaccines (though the link here is not entirely clear). These reactions occur in about 1 per million for most vaccinations. These reactions can be serious, but the risk comes primarily from not recognizing the symptoms quickly enough or not being near a doctors office at the time the reaction becomes serious. In a doctors office or a hospital, these reactions are easily managed. It is extremely rare for children to suffer any long-term health effects from vaccine-induced adverse reactions. Some particular vaccines have specific side effects, like immunosupression or autoimmune reactions, but these are more rare then allergic reactions. Another risk is simply fainting after receiving the vaccine – there is a documented case of one person dying this way, after hitting their head during the fall.

So let’s put these risks into context. Let’s say, conservatively, the risk of any serious side effect of a vaccine is 2 in 1 million, and a typical child gets about about 30 vaccines before they turn 18. In this case, the risk of a serious side effect from childhood vaccines is 60 in 1 million, or 1 in 16,666. How does this stack up against other lifetime risks we face?

You get the point. Vaccines are extremely “safe” when compared to many of the activities we perform every day. You are more likely to win an Oscar in your lifetime than have any sort of adverse reaction to a vaccine. Among drugs (and vaccines are regulated the same as drugs), vaccines are also much safer than average. About 150-440 people per year die from taking too much acetaminophen (Tylenol), a medication you can literally pick up in any pharmacy or convenience store. People die from allergic reactions to non-vaccine drugs (particularly antibiotics) at a much higher rate than vaccines – about 1,500 such deaths were documented form 1999-2010, and of course, opioid pain killers kill thousands of people per year – you are 152-times more likely to die from an overdose of opioid painkillers in your life than you are to experience even a moderate adverse effect (beyond a sore arm and a mild fever) from a vaccine.

In terms of the benefit side of the equation, vaccines are without a doubt one of the single greatest achievement in the history of our species. Before vaccines were developed, common diseases like measles, rubella, and diphtheria killed thousands a year. Occasionally, epidemics of particularly virulent viruses would killed tens or even hundreds of thousands.

So what would happen if we stopped vaccinating? If a very few people fail to get vaccinated, the effect is usually minimal. The damage is likely to be limited to small outbreaks, like the Minnesota measles outbreak that sickened 79 people and sent 22 to the hospital. However, if a large percentage of the population skipped vaccinations, thousands would die from common preventable disease. Remember the odds of an experiencing an adverse effect form a vaccine is 1 in 16,666. Here are the odds of death from some of the diseases these vaccines prevent (all numbers for the untreated disease).

Odds of death from bacterial meningitis: 1 in 1.4

Odds of death from a tetanus infection: 1 in 10

Odds of death from a diphtheria or polio infections: 1 in 20

Odds of death from a mumps infection: 1 in 72

Odds of death from a measles infection: 1 in 500

You get the point. In terms of benefit/risk, vaccines tilt the odds of survival greatly in your favor. It is likely that vaccines have saved more lives than any other invention in human history. In fact, it’s likely that it’s not even close.

Next up, data sources and conspiracy theories. Click here for part 2.

• Data for relative risks in this post came from the CDC website and here.