Serious side effects of vaccines are rare. What does that mean?

The Pediatric Insider

© 2014 Roy Benaroch, MD

“Serious side effects of vaccines are rare.”

Vaccines are not 100% safe. Like any medical intervention, there’s some risk (honestly, like anything at all, anything we do, there’s some risk. But let’s not get sidetracked here.) Side effects, including serious side effects, can happen after vaccines. What are these reactions, really? How often do they occur?

Here, I’m only talking about genuine, established side effects. Things are genuinely, scientifically, reliably linked to vaccines. Some things that had once been thought be a potential side effect of vaccines are now known to have been caused by other conditions (like seizures and encephalopathy after DTP, now known to be most-often caused by a rare genetic condition called Dravet Syndrome, that would have occurred whether the child was immunized or not.) There are also side effects reported that are clearly unrelated, like choking on a bean in the trachea or turning into the Incredible Hulk. We’ll ignore those, and concentrate on the real, serious, potentially deadly side effects that have been documented to be caused by vaccines. I’m going to list all of them, for every vaccine. If I missed any, please add in the comments.

Any vaccine – Serious allergic reactions can occur. These do happen, though the rate of serious reactions depends on the vaccine. For most immunizations, the rate is less than 1 in 1 million; however, some very-rarely used vaccines can have a higher rate. The yellow fever vaccine, for instance, causes severe allergic reactions in about 1 in 55,000 people; anthrax vaccine is estimated to cause severe reactions in 1 in 100,000. Almost all severe allergic reactions occur within minutes of vaccination, and health care facilities who give vaccines should have people trained to treat rare reactions like these.

Influenza – The Pandemrix brand of influenza vaccine, which was never licensed or used in the United States, has been linked as a cause of narcolepsy in about 1 in 55,000 vaccine recipients in several countries in Europe. This product was only used during the 2009-2010 season. The CDC is currently sponsoring an international study to try to better understand this, and why that one formulation seemed to be a unique trigger for this rare condition.

In 1976, a different specific Swine Flu vaccine was linked to about 450 cases of Guillian-Barre Syndrome (GBS), a neurologic disorder that was estimated to occur in about 1 in 100,000 people who got that specific vaccine that year. The baseline rate of GBS is probably 1-2 per 100,000, so when 45 million doses of vaccine were given in 1976, some cases were going to occur coincidentally. Substantial studies have shown that other flu vaccines from more-recent years do not cause GBS. Ironically, influenza disease itself causes more GBS than even the 1976 Swine Flu vaccine is purported to have caused, and even if that association were true influenza vaccination would prevent far more GBS than it would trigger.

Japanese encephalitis – Rarely used in the United States, the Japanese Encephalitis vaccine has been linked to prolonged arm and shoulder pain among vaccine recipients. I could not find an exact rate, but this appears to be an uncommon reaction.

MMR — About 1 in 30,000 people given a dose of MMR will have a drop in their platelet count, which can predispose to bleeding. The rate of low platelets is much higher in real measles than after the vaccine, so, again, ironically MMR probably prevents more cases of low platelets than causes it. This condition is temporary and almost always requires no treatment at all.

Polio — The oral polio vaccine, no longer used in the United States, could trigger genuine, full-blown polio in some people—probably about 8 per year in the entire US, back when we used the oral version. We’ve been using only the injected polio since the mid-1990s, which carries zero risk of causing polio.

Rotavirus – Rotavirus vaccines carry a small risk of causing an intestinal blockage called “intussusception.” This condition is treatable, though it often requires a brief hospitalization. The risk was highest after the first doses of the original brand of vaccine, Rotashield, which was withdrawn from the market; the risk after current brands is probably in the range of 1-3 in 100,000. However, rotavirus itself, the real infection, is also a cause of intussusception. To put this in perspective: using the high end of the risk estimates, about 40-120 vaccinated infants may develop intussusception each year in the USA, compared to 65,000 infants who had been hospitalized for rotavirus illness each year prior to the vaccine becoming available.

Smallpox – Routine smallpox vaccinations stopped by 1970 in the US, but a smallpox vaccine is available for high-risk researchers and military people and others thought to be at risk of exposure. The vaccine can cause heart problems in 1 in 175 people, and there is a risk that the vaccine virus can spread on the skin of a vaccinated person or contacts, especially when the skin is damaged or there are immune problems.

Yellow fever – Used only in certain travelers, some kinds of yellow fever vaccine can causes severe neurologic problems (about 1 in 125,000) or death, especially in elderly people (1 in 500,000).

That’s it—that’s the list. All of the serious, lasting, you-need-to-worry about side effects. You’ll notice that almost all of the really serious side effects occur only with vaccines that aren’t likely to be recommended for your children. Most of the routine childhood vaccines (DTaP, HIB, pneumococcal conjugate, hepatitis B, hepatitis A, chicken pox, meningococcal conjugate, human papilloma virus) only carry a very rare risk of allergic reactions, and even those are entirely treatable and temporary. In other words, science has failed to find any evidence for any real, lasting, serious vaccine reactions among any of the vaccines currently recommended for routine use in children in the United States.

When we say “serious side effects are rare,” we mean “serious side effects are very very very rare, and really only happen with vaccines that we don’t even use.”

What parents need to worry about are diseases, not vaccines. Don’t let the scaremongers and internet rumors sway you. The risk of a serious, lasting side effect from any routine childhood vaccine is just about zero. Make sure your children are safe and protected. Vaccinate!

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3 Comments on “Serious side effects of vaccines are rare. What does that mean?”

  1. Deb Stover Says:

    Pertussis vaccine (DPT) is missing from your list. My daughter went into shock and could not be awakened after one dose. After 24 hours, she was fine. After that, she received only a DT vaccine.

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  2. Dr. Roy Says:

    Deb, what happened was scary, but it didn’t actually harm anyone. This kind of reaction, formally called a “hypotonic-hyporesponsive” episode, is not “shock”, and it isn’t a contraindication to future doses of pertussis-containing vaccine (tho it is a “precaution”). The current acellular DTaP, in use since mid-1990s, causes fewer episodes of this nature than the older DTP.

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