Tag: risk perception

Is It a Vaccine Reaction?

Why do anti-vaccine folks think that there are so many vaccine reactions?

It is mostly because they think that anything bad that happens after someone is vaccinated, even if it is weeks or months later, must have been caused by the vaccine.

“Differentiation between coincidence and causality is of utmost importance in this respect. This is not always easy, especially when an event is rare and background rates are not available.”

Heininger on A risk-benefit analysis of vaccination

Of course, this discounts that fact that most people have a basic risk, often called the background rate, for developing most of these very same conditions, and they can just coincide with getting vaccinated.

Put more simply, the “reaction” would have happened whether or not they had been vaccinated.

“…when a number of well-controlled studies were conducted during the 1980s, the investigators found, nearly unanimously, that the number of SIDS deaths temporally associated with DTP vaccination was within the range expected to occur by chance. In other words, the SIDS deaths would have occurred even if no vaccinations had been given.”

WHO on Six Common Misconceptions About Immunization

That doesn’t mean that everything automatically gets blamed on coincidence though.

Is It a Vaccine Reaction?

Vaccine adverse events can be reported to VAERS online or using a downloadable form.
Vaccine reactions can be reported to VAERS online or using a downloadable form.

When trying to determine if a child has had a vaccine reaction, experts typically go through a series of questions, looking at the evidence for and against :

  • How soon after the vaccine was given did the reaction occur? Was it minutes, hours, days, weeks, months, or years later?
  • Is there any evidence that something else could have caused the reaction?
  • Is there a known causal relation between the reaction and the vaccine?
  • Is the reaction a table injury?
  • Is there evidence that the vaccine does not have a causal association with the reaction?
  • Do any lab tests support the idea that it was a vaccine reaction?

Why is it important to consider these and other questions?

Because most of us are very good at jumping to conclusions, are quick to place blame, and like to know the reasons for why things happen.

We don’t like to think that things are just caused by coincidence.

Post hoc ergo propter hoc (after this, therefore, because of this).

We are especially good at linking events and often automatically assume that one thing caused another simply because it occurred afterwards.

It is incident to physicians, I am afraid, beyond all other men, to mistake subsequence for consequence.

Dr Samuel Johnson

But we also know that correlation does not imply causation. And because of the great benefits of vaccines, it is important to find strong evidence for a correlation before we blame vaccines for a reaction.

Too often though, the opposite happens. Despite strong evidence against a correlation, parents and some pediatricians still blame vaccines for many things, from SIDS and encephalitis to autism.

Background Rates vs Vaccine Reactions

Although anti-vaccine folks are always calling for vaccinated vs unvaccinated studies to further prove that vaccines are indeed safe, much of that work is already done by looking at the observed rate of possible reactions and comparing them to the background rate of reactions and conditions.

We often know how many people are expected to develop certain conditions, from seizures and type 1 diabetes mellitus to acute transverse myelitis and juvenile and rheumatoid arthritis.

“On the basis of the reviewed data, if a cohort of 10 million individuals was vaccinated in the UK, 21.5 cases of Guillain-Barré syndrome and 5.75 cases of sudden death would be expected to occur within 6 weeks of vaccination as coincident background cases. In female vaccinees in the USA, 86.3 cases of optic neuritis per 10 million population would be expected within 6 weeks of vaccination. 397 per 1 million vaccinated pregnant women would be predicted to have a spontaneous abortion within 1 day of vaccination.”

Black et al on Importance of background rates of disease in assessment of vaccine safety during mass immunisation with pandemic H1N1 influenza vaccines

Intussusception is a good example of this.

This might surprise some folks, but we diagnosed and treated kids with intussusception well before the first rotavirus vaccines were ever introduced. And then, it was only after the risk of intussusception after vaccination exceeded the background rate that experts were able to determine that there was an issue.

Background rates also explain why unvaccinated kids develop autism. It’s not a coincidence.

“Knowledge of the background incidence rates of possible adverse events is a crucial part of assessing possible vaccine safety concerns. It allows for a rapid observed vs expected analysis and helps to distinguish legitimate safety concerns from events that are temporally associated with but not necessarily caused by vaccination.”

Gadroen et al on Baseline incidence of intussusception in early childhood before rotavirus vaccine introduction, the Netherlands, January 2008 to December 2012

Fortunately, studies have never found an increased risk above the background rate for SIDS, non-febrile seizures, and other things that anti-vaccine folks often blame on vaccines. So when these things happen on the same day or one or two days after getting vaccinated, it almost certainly truly is a coincidence. It would have happened even if your child had not been vaccinated, just like we see these things happen in the days before a child was due to get their vaccines.

For example, using background incidence rates in Danish children, one study found that if you vaccinated a million children with a new flu vaccine, you could expect that naturally, after seven days, you would see:

  • facial nerve palsy – one case
  • seizures – 36 cases
  • multiple sclerosis – one case
  • type 1 diabetes – three cases
  • juvenile and rheumatoid arthritis – three cases

After six weeks, those numbers of course go up. In addition to 4 kids developing MS, 20 develop diabetes, 19 develop arthritis, and 218 have seizures, and there would have been at least two deaths of unknown cause.

Would you blame the flu shot for these things?

What flu shot?

This was a “hypothetical vaccine cohort” that used 30 years of data from the Danish healthcare system to figure out background rates of each condition.

“In addition, the expected number of deaths in Japan following an estimated 15 million doses of H1N1 vaccine administered would be >8000 deaths during the 20 days following vaccination, based on the crude mortality rate.”

McCarthy et al on Mortality Rates and Cause-of-Death Patterns in a Vaccinated Population

Looking at background rates is especially helpful when folks report about vaccine deaths.

Using the Japan example that McCarthy studied, if they had looked at background rates, then all of a sudden, the 107 deaths they found after 15 million doses of H1N1 vaccine were given in 2009 would not have been so alarming. Background rates would have predicted a much, much higher number of deaths to naturally occur in that time period simply based on crude mortality rates.

Again, none of this means that possible vaccine reactions are dismissed as being coincidences. They just aren’t immediately assumed to have been caused by vaccines, because vaccines are necessary and a lot of research has already gone into demonstrating that vaccines are safe and vaccines continue to go through routine safety monitoring to make sure they stay safe.

What to Know About Evaluating Vaccine Reactions

Vaccines are safe and many of the things that folks think are vaccine reactions can be explained by looking at the background rates for these conditions and understanding that they would have happened anyway.

More on Evaluating Vaccine Reactions

How Many People Die in the USA Every Year from Being Vaccinated?

We know that vaccines work to save lives from vaccine-preventable disease.

If you are at all hesitant about vaccines and are doing your research, you have likely come across the myth that vaccines are more dangerous than the diseases they protect us against though.

This is only because most people don’t remember the pre-vaccine era when measles, polio, small pox, and diphtheria, etc., were big killers. So even though vaccine side effects are about the same as they always have been, they can become a much bigger focus for some people because they don’t see any of the mortality or morbidity from the diseases that the vaccines have gotten so good at preventing.

immunization-program-stages
As more people are vaccinated and diseases disappear, they forget how bad those diseases are, skip or delay getting their vaccines, and trigger outbreaks. Photo by WHO

It is at this crossover point that anti-vaccine folks are able to get away with pushing myths, such as like more people die from the MMR vaccine than from measles.

They don’t.

How Many People Die in the USA Every Year from Being Vaccinated?

Although vaccines are not perfectly safe, it is extremely rare for a vaccine reaction to be deadly.

“As for vaccines causing death, again so few deaths can plausibly be attributed to vaccines that it is hard to assess the risk statistically.”

WHO on Six common misconceptions about immunization

So why do anti-vaccine folks think that they are more common than they really are?

That’s an easy question to answer.

“Differentiation between coincidence and causality is of utmost importance in this respect. This is not always easy, especially when an event is rare and background rates are not available.”

Heininger on A risk-benefit analysis of vaccination

They often believe than anything and everything that happens after someone is vaccinated, even if it is weeks or months later, must have been caused by the vaccine. This discounts that fact that most people have a basic risk, often called the background rate, for developing these conditions that can coincide with getting vaccinated. It also explains why they believe in so many so-called vaccine induced diseases.

Another reason is that they also misuse VAERS reports when talking about vaccine deaths.

“In a review of reports of death following vaccination submitted to the Vaccine Adverse Event Reporting System (VAERS) from the early 1990s, the Institute of Medicine concluded that most were coincidental, not causally associated.”

Moro et al on Deaths Reported to the Vaccine Adverse Event Reporting System, United States, 1997–2013

Not surprisingly though, studies have shown that most of the deaths in VAERS are not actually related to vaccines.

In fact, most of the things that anti-vaccine folks blame on vaccines, including things you see in many of their vaccine-injury stories, are not related to vaccines.

How Many People Die in the USA Every Year from Vaccine-Preventable Diseases?

Fortunately, most people are vaccinated, and deaths from  vaccine preventable diseases are tremendously below what they were in the pre-vaccine era.

Most people will be surprised to know that they aren’t zero though.

People do still get vaccine-preventable diseases in the United States.

And tragically, people do still die of vaccine-preventable diseases in the United States.

For example, in 2015:

  • there were at least 37 cases of perinatal hepatitis B infections
  • five infants and children less than age 5 years died of rotavirus disease
  • a 14-month-old died of Hib meningitis
  • an infant died of pneumococcal meningitis
  • a 3-year-old with congenital rubella syndrome died
  • at least two teens died of meningococcal meningitis
  • a woman in Washington died of measles – the immunosuppressed women was exposed to an outbreak in Clallam County that mostly included intentionally unvaccinated kids
  • 85 kids died of the flu

Of course, worldwide, especially in developing countries, the number of deaths are much higher, which is a good reminder of what would happen if more of us stopped vaccinating!

And it is an even better reminder that you have to look at the number of deaths from vaccine-preventable diseases today in the context that most people are vaccinated and protected.

If you are truly looking at a risk vs benefit analysis of whether or not to get vaccinated, it is still the great benefit of avoiding vaccine preventable diseases vs the very small risks of getting vaccinated that you should think about.

“I also warn them not to share their fears with their neighbors, because if too many people avoid the MMR, we’ll likely see the diseases increase significantly.”

Dr. Bob Sears in The Vaccine Book

It is also the small risks of getting vaccinated vs the much greater risk of going back to the pre-vaccine era if you decided to skip or delay any vaccines.

It is not that you have been scared into thinking that the risks of  vaccines outweigh their benefits.

“Millions of vaccinations are given to children and adults in the United States each year. Serious adverse reactions are rare. However, because of the high volume of use, coincidental adverse events including deaths, that are temporally associated with vaccination, do occur. When death occurs shortly following vaccination, loved ones and others might naturally question whether it was related to vaccination. A large body of evidence supports the safety of vaccines, and multiple studies and scientific reviews have found no association between vaccination and deaths except in rare cases.”

Miller et al on Deaths following vaccination: What does the evidence show?

It is not that the risk of getting a vaccine preventable disease is low because you might be able to get away with hiding in the herd.

It is not that the risk of getting a vaccine preventable disease is low because you are counting on everyone else in the world to get vaccinated and eliminate or eradicate the disease and your risk.

If too many parents who are on the fence start believing that their kids have zero risk of getting polio and other vaccine-preventable diseases and continue to skip or delay vaccines, then boom, we are back to the days when outbreaks would close schools and kids would suffer from the devastating effects of these diseases.

Even the schools were closed in San Antonio when polio came to Texas in 1946.
Even the schools were closed in San Antonio when polio came to Texas in 1946.

While anti-vaccine folks won’t have such an easy time convincing people that these diseases are mild anymore, none of us want to wait for more outbreaks to occur before folks get the message that vaccines are safe and necessary.

What to Know About Vaccine Deaths

Despite what anti-vaccine folks would have you believe as they try to scare you away from vaccinating and protecting your kids, vaccines are safe and necessary and vaccine deaths are very rare.

More on Vaccine Deaths

What Are the Risks of Vaccines?

Vaccines are very safe, but they are not 100% risk free.

They are certainly not as high risk as some anti-vaccine folks will have you believe though.

“Vaccine hesitation is associated with perceived risk. Since vaccine-preventable diseases are rare, an adverse event from a vaccine is perceived by the parent to be of greater risk. Risk perception is critical.”

AAP on Addressing Common Concerns of Vaccine-Hesitant Parents

And when you consider their great benefits, it is easy to see why the great majority of parents get their kids fully vaccinated and protected against all recommended vaccine-preventable diseases.

Risk Perception and Vaccine Hesitancy

Even though the risks and side effects of vaccines are very low, some people think that they are much higher. This is often amplified because of vaccine scare stories and the misinformation found on anti-vaccine websites.

“No intervention is absolutely risk free. Even the journey to a physician’s office with the intention to receive a vaccination carries the risk of getting injured in an accident. With regards to risks of vaccination per se, one has to distinguish between real and perceived or alleged risks.”

Heininger on A risk–benefit analysis of vaccination

Other problems with risk perception include that some people:

  • can be more likely to avoid risks that are associated with an action or having to do something vs. those that involve doing nothing or avoiding an action, even if inaction (skipping or delaying a vaccine) is actually riskier
  • often think about risks based on their own personal experiences (you remember someone’s vaccine injury story), rather than on scientific evidence

These biases in the way we think about risk can actually lead us to make risky choices and they help explain why some people are still so afraid of vaccines. Parents might think the risk of a possible side effect, some of which don’t even exist, is worse than the risk of getting a vaccine-preventable disease, getting someone else sick, or starting an outbreak. Parents also often underestimate the risk of their decision to not vaccinate their child.

“As much previous research claims, this study confirms that individuals characterized by greater trust of healthcare professionals and the possession of more vaccine-related knowledge perceive higher levels of benefits and lower levels of risks from vaccinations.”

Song on Understanding Public Perceptions of Benefits and Risks of Childhood Vaccinations in the United States

So what’s the answer? It is likely for folks to get better educated about vaccines, including getting a good understanding of both their benefits and risks.

What Are the Risks of Vaccines?

Again, vaccines are not 100% safe or risk free.

Most vaccines have some common, mild side effects, which might include (depending on the vaccine):

Vaccine Information Statements from the CDC highlight the risks of each vaccine.
Vaccine Information Statements from the CDC highlight the risks of each vaccine.
  • fever, typically low-grade
  • redness or swelling where the shot was given
  • soreness or tenderness where the shot was given
  • fussiness
  • headache
  • tiredness or poor appetite
  • vomiting
  • mild rash
  • diarrhea
  • swollen glands

How commonly do they occur?

It depends on the vaccine and side effect, but they range from about 1 in 50 to 1 in 3 people. These side effects are typically mild and only last a day or two. And they don’t cause lasting problems.

While not all possible side effects are mild, those that are more moderate or severe are much more uncommon. Febrile seizures, for example, only happen after about 1 out of 3,000 doses of MMR and some other vaccines. And while scary, febrile seizures, crying for 3 hours or more, or having a very swollen arm or leg, some other uncommon vaccine side effects, also don’t cause lasting problems.

Fortunately, the most severe side effects, including severe allergic reactions, are only thought to happen in less than 1 out of a million doses. And although these types of severe reactions can be life threatening, they are often treatable, just like severe allergic reactions to peanuts. For others, like encephalitis, although they are table injuries, it isn’t clear that they are even side effects of vaccines, since they occur so rarely.

All of these side effects can be reported to the Vaccine Adverse Event Reporting System (VAERS), either by your doctor or yourself.

“No medical product or intervention, from aspirin to heart surgery, can ever be guaranteed 100% safe. Even though we will never be able to ensure 100% safety, we know that the risks of vaccine-preventable diseases by far outweigh those of the vaccines administered to prevent them.”

World Health Organization

In addition to side effects, some other risks of getting vaccinated might include that your vaccine didn’t work, after all, although vaccines work very well, they are not 100% effective. You might also, very rarely, be given the wrong vaccine or the right vaccine at the wrong time.

Many other things, including so-called vaccine induced diseases, aren’t actually a risk of vaccines at all. Remember, autism, SIDS, multiple sclerosis, and shaken-baby syndrome, etc., are not a risk of vaccines.

What to Know About the Risks of Vaccines

Any small risks of getting vaccinated, including side effects that are often mild, are not a good reason to think about skipping or delaying a vaccine, especially when you thoughtfully consider all of their great benefits.

More About the Risks of Vaccines