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Emotions run high on the topic of vaccination. People resent being forced to make choices for their children that they are not comfortable with, and others resent having their children put at risk when their classmates aren’t vaccinated. There are active protest groups on both sides, and in the meantime, cases of preventable disease are on the rise.
The tally of measles cases in the United States this year has reached 626, as of April 19. This exceeds the total number of yearly cases for 2018 and 2017. If contagion continues at this rate, the nation is on track for the most measles cases per year in the last decade. Authorities have even declared a health emergency in parts of Brooklyn, New York.
This caseload is still low by historical standards. In the 1950s, in the U.S., a typical year would see 3 million to 4 million measles cases. The overall decline in measles since the 1950s happened for the same reason that measles rates are currently rising: the ebb and flow of vaccination.
The measles vaccine was introduced in 1963. By 1968, the number of yearly measles cases had dropped from 4 million to under 50,000. By the early 1980s, the figures were close to zero.
In more recent years, however, skepticism of routine childhood vaccination has increased with the so-called anti-vax movement. A combination of celebrity anti-vaxxers, and a movement toward more personal choice in medicine generally, has laid the groundwork for a small but influential population who oppose vaccines. People against vaccination argue it has risks, that vaccines can cause autism or other unspecified injuries. Proponents of vaccination say this is nonsense, anti-science, and damaging to the health of children.
From my perspective, it always helps to look at the data.
I’ve just written a book, Cribsheet, on how to use evidence and data to make choices about early parenting — whether to breastfeed or circumcise, the right age for potty training, and so on — and in doing so, I reflected a lot on these vaccine controversies. Based on my review of the evidence and data, I believe vaccines are a good idea.
When I decided to write about vaccines in Cribsheet, I thought about having a one-line chapter which said, “Vaccines are safe and effective.” And then I’d move on to other topics — say, co-sleeping, where the evidence is more nuanced and interesting. But as I thought about it, I realized that this dismissive attitude may be precisely the problem, and the reason why the pro-vaccination side seems to be losing.
Sleep-deprived parents do not generally think in statistical terms.
If you look at anti-vaccination websites (please don’t), many of them seem evidence-based; they cite papers and studies to support their position. On the other side, organizations like the U.S. Centers for Disease Control (CDC) and the American Academy of Pediatrics (AAP) assure people that vaccination is safe. But the latter groups rarely confront the anti-vaccination literature head-on. There is little effort to explain why the papers cited on anti-vaccination websites are problematic. It can end up seeming as though the anti-vaccination side is serious and evidence-based, and the pro-vaccine side is just dismissively insisting that you trust them because they are experts.
In fact, the case in favor of vaccines is based on extensive research and evidence. I know because I read, in detail, a 900-page tome entitled “Adverse Effects of Vaccines: Evidence and Causality,” put out by the Institute of Medicine. This book was a multiyear effort by a huge group of scientists to think really carefully about the possible risks of vaccines. The authors evaluated evidence from more than 12,000 papers, looking for links between vaccines and “adverse events.” They seriously considered all the possible risks. And their analysis is careful, thoughtful, and not dismissive.
The starting point for these authors is the CDC adverse event reporting system, which is an online resource where people can report if they think their child has been adversely affected by vaccinations. If you search on here, you can find all kinds of parent-reported links about vaccine consequences for their children.
Some may argue that these reports are enough to at least show some link between vaccination and some bad outcome — if someone says their child was damaged, isn’t that enough? But evidence of this type is tenuous at best.
Imagine if people believed that cutting an infant’s fingernails was medically dangerous — that it led to illness or other complications. And imagine we set up an adverse event reporting system for fingernail cutting.
In all likelihood, you’d get a very wide range of reports. There would be parents reporting that the day after they cut their infant’s fingernails, the baby came down with a terrible fever. Others would say they had a very liquid-looking poop. You’d get reports of children who didn’t sleep well for days after the fingernail cutting, and others about babies crying uncontrollably for hours.
These would all be true things that happened. But they wouldn’t be causally linked to the fingernail cutting. Sometimes infants get a fever; sometimes they have weird poops. Most babies do not sleep, and others cry a lot. In order to figure out whether there was any real link, you’d need to know the general base rate of these events — how likely people are to report them when there was no fingernail cutting. But that isn’t something we have a reporting system for. There is no website where you can report every time your kid has an unusual poop. And people, particularly sleep-deprived parents, do not generally think in statistical terms. Near fear looms large.
To know in more certain terms, you’d have to piece together whether these adverse events really seem more common among babies whose nails are cut than those whose aren’t. This is especially hard for things that happen all the time, like when a baby cries.
In your fingernail-reporting system, you probably would also learn something. You’d get a lot of reports of finger injury — cuts in need of Band-Aids. This is not something that happens all the time, and there is an obvious mechanism for the connection with nail cutting. So, you probably would conclude that fingernail cutting is linked to accidental finger cutting, which is true (I know from experience).
This hotline example — while hypothetical — has a direct parallel with claims about the link between autism and vaccination. It is true that some children have autism. And in some cases, this autism is recognized around the time of some vaccinations. On the flip side, many children are vaccinated and do not develop autism. Without knowing the rate of autism development in unvaccinated children — the base rate — we cannot draw conclusions from these example cases.
When the Institute of Medicine report was produced, the authors did look at these adverse reports, but they also looked for corroborating — or refuting — evidence. Is there a biological reason to think some link exists? Are there academic studies with large numbers of people which evaluate this link? Putting this all together, they try to parse what the real risks are.
It is tempting to give up on trying to talk about vaccine safety — to legislate the issue rather than winning over hearts and minds.
In the end, the authors do identify a few risks. Vaccines can cause allergic reactions, and for immunocompromised children there are vanishingly small risks of very severe consequences. These risks are “real” in the sense of being causally linked to vaccines, but — and I cannot emphasize this enough — they are tiny and irrelevant to nearly everyone. Allergic reactions occur in an estimated 0.22 of 100,000 vaccines. That means for a half a million vaccinated children you’d expect one to have a treatable allergic reaction. You will know if your child is immune compromised, and children in this group are typically not vaccinated for this reason. Yes, there are these vaccine risks, but that is different from saying they are important enough to reject vaccination; they are not.
This report refutes a number of purported links, most notably the link to autism. The authors cite, for example, data on more than 500,000 children in Denmark in which autism rates for vaccinated and unvaccinated children are compared. Here, we have our comparison group. They noted that vaccinated children are, in fact, less likely to have autism. A more recent study, just released a few weeks ago, uses updated data from the same source to draw the same conclusions.
In the end, the weight of the evidence really does say that vaccines are safe and effective. And not just because experts say they are, but because the evidence says that they are.
As I wrote about all of this, it was hard not to wonder whether I, like the rest of the pro-vaccination community, was tilting at windmills. I am not the first person to argue that vaccines do not cause autism, and I will certainly not be the last. And there is evidence — some of which I have produced myself — that vaccination rates may increase more in response to disease outbreaks, or to changes in school vaccination rules.
One of the early topics of my academic work was vaccination rates in developing countries. In many places, vaccination is limited by resource availability and not by parental resistance. In these places, people die of measles. A 2019 outbreak in Madagascar has killed an estimated 900 children. I think it is clear that routine vaccination of children is all that stands between us and significant numbers of measles deaths.
It is tempting to give up on trying to talk about vaccine safety — to legislate the issue rather than winning over hearts and minds. At the end of the day, though, I think we should keep the conversation going. Forcing people to vaccinate their children by withholding public schooling is effective, but it would be much better if we could convince parents of the value of shots and have them come to it on their own. Not everyone can be convinced by the approach of looking hard at the evidence and evaluating causal links. But I hope some people can. We cannot afford to continue to put children at risk for potentially deadly diseases due to unfounded fears.