AndEvil Mr. Vaccine and the consequences of vaccination.

There’s nothing like cold hard data to counteract opinion and propaganda. The anti-vaccine movement hit upon a clever marketing phrase with their “Too Many, Too Soon” campaign. Unfortunately, it is often difficult to capture the complexity and nuance of scientific data with a witty slogan, so such slogans tend to work better for those who don’t really care about such things as scientific data.

I’ll give it a try in any case: how about “too few, too late.” Or maybe, “A day late and an antigen short.”

OK, now you know why I’m not in the marketing business. So let’s talk about the actual scientific data.

The recommended vaccine schedule is not, it turns out, arbitrary or designed to maximize the profits of the vaccine industry. The Center for Disease Control (CDC) recommended vaccine schedule is designed to give children vaccines as soon as they need them and are old enough to handle them – maximizing benefit while minimizing risk. Booster shots are optimized to produce a sufficient antibody response for maximal protection. I don’t think anyone would argue that the schedule is perfect, but it is rational and evidence-based.

Also, no one argues that the risk of vaccines is zero. No medical intervention has a zero risk. In medicine we look at risk vs benefit. Vaccines have one of the highest (if not the highest) benefit to risk ratios of any major medical intervention we have developed. It is ironic that it is attacked by ideologues as unsafe.

One potential risk of vaccines is that the immune response they elicit may cause a fever which in turn might cause, in susceptible children, a febrile seizure. In rare cases vaccinations have been followed by encephalitis (brain inflammation) with not only seizures but more serious neurological complications. The incidence of post-vaccination encephalitis is 1-2 cases per million vaccines, and this is just association, without knowing how many represent true cause and effect.

A recently-published study sheds further light on the risk of seizures following vaccination, and also compares the recommended vaccine schedule to delayed schedules.” Timely Versus Delayed Early Childhood Vaccination and Seizures“, was recently published in the journal, Pediatrics. They found:

METHODS: In a cohort of 323 247 US children from the Vaccine Safety Datalink born from 2004 to 2008, we analyzed the association between the timing of childhood vaccination and the first occurrence of seizure with a self-controlled case series analysis of the first doses of individual vaccines received in the first 2 years of life.
RESULTS: In infants, there was no association between the timing of infant vaccination and postvaccination seizures. In the second year of life, the incident rate ratio (IRR) for seizures after receipt of the first measles-mumps-rubella vaccine (MMR) dose at 12 to 15 months was 2.65 (95% confidence interval [CI] 1.99–3.55); the IRR after an MMR dose at 16 to 23 months was 6.53 (95% CI 3.15–13.53). The IRR for seizures after receipt of the first measles-mumps-rubella-varicella vaccine (MMRV) dose at 12 to 15 months was 4.95 (95% CI 3.68–6.66); the IRR after an MMRV dose at 16 to 23 months was 9.80 (95% CI 4.35 –22.06).

What this means is that, in the first year of life, there was no difference in seizure risk between children who received the full vaccine schedule on time, and those who had delayed or reduced vaccines. In this age group, alternate vaccine schedules had no benefit on the risk of seizures.

In the second year of life, however, those who delayed the MMR vaccine to 12-15 months had almost triple the seizure risk, while those delaying to after 16 months had a 6 times greater risk. This increased risk was even higher for the MMRV vaccine.

This data strongly suggests that getting vaccines on time has a lower risk of post-vaccination febrile seizures than delaying to the second year of life, when the inherent risk is greater.

While this is a large study with rigorous methods, it is a retrospective cohort study, not a prospective randomized study. Therefore it is possible that there are confounding factors. Still it provides strong evidence that the current vaccine schedule is superior to alternative or delayed schedules.

A 2010 study using the same database found no correlation between timely vaccines and any adverse neurological outcome. In other words – delaying the vaccine schedule did not reduce the incidence of neurological disorders.

Further there are many studies showing that delayed or reduced vaccine schedules increase the risk of contracting the diseases from which the vaccines protect.


The optimal timing of vaccines and number of boosters to be given is an important question in order to optimize the benefit and minimize the risks of vaccines. The current schedule, while it requires ongoing research and monitoring, is based on the best evidence that we currently have.

Popular delayed or alternate vaccine schedule are not based on evidence. They are based on fear and marketing.

It should come as no surprise that the evidence supports the use of an evidence-based vaccine schedule over a fear-based vaccine schedule.


Posted by Steven Novella

Founder and currently Executive Editor of Science-Based Medicine Steven Novella, MD is an academic clinical neurologist at the Yale University School of Medicine. He is also the host and producer of the popular weekly science podcast, The Skeptics’ Guide to the Universe, and the author of the NeuroLogicaBlog, a daily blog that covers news and issues in neuroscience, but also general science, scientific skepticism, philosophy of science, critical thinking, and the intersection of science with the media and society. Dr. Novella also has produced two courses with The Great Courses, and published a book on critical thinking - also called The Skeptics Guide to the Universe.