Are your vaccinations up to date?

Are your vaccinations up to date?

“Vaccine hesitancy” is the research label for your indecision about whether or not to get a vaccination when offered. In the past, patients rarely questioned the need for vaccines. Perhaps it was due to differences in the doctor patient relationship. Or perhaps it was due to the constant reminders of what happened without the vaccine. For those of us old enough to have lived through the introduction of some vaccines, there were reminders of the diseases they prevent. I still have scars on my legs from chickenpox. But more haunting are the vivid memories of my friend Jim as he dragged his uncooperative legs around my 4th grade classroom using crutches with leg and body braces. Jim had survived polio.
So I can’t help wondering how sharing our past, telling stories of the bad old days before vaccines, might impact our willingness to be accurately informed about the net benefits of vaccination.
One of my favorite storytellers of disease is Berton Roueche. For years he wrote his mysteries of disease and the detectives who solved them in the New Yorker magazine and published several books of the short stories. They are mostly out of print and hard to find but they are spellbinding stories. He painted vivid pictures of the effects of the diseases, like his description of tetanus, a vaccine preventable disease, in his story, “A Pinch of Dust”. Using quotes from Hippocrates and another ancient physician, Roueche presents an unforgettable image of a patient whose first symptoms of difficulty talking were followed quickly by locked teeth and jaws and only three days later by muscle contractions of the back so severe that the head became bent down the back between the shoulder blades while the spine arched so severely that it appeared the patient was trying to touch his head to his heels. Six days later the patient was dead.
Roueche also describes the bacterium that causes tetanus, Clostridium tetani, and the incredible strength of the toxin it makes (“one of the most venomous poisons known to man”). And, he explains, it is an essentially incurable disease. Since the time of his writing, intensive care therapeutic support options have improved. Still, you may want to read the wikipedia description of treatment for severe tetanus, especially if you aren’t up to date on your Tdap vaccine or don’t know when you had your last vaccine. Or read the CDC description of your risk of death if you get tetanus. It’s one out of every 10 people, even with the best medical care.

You need the vaccine every ten years.

I’m not recommending fear as a strategy for reducing vaccine hesitancy. You can review the state of the literature on how to address vaccine hesitancy by going to PubMed and entering vaccine hesitancy. Or start with this systematic review. Spoiler alert -  the causes of vaccine hesitancy are multifactorial and context specific and thus likely to need multi pronged interventions to address.

But stories from a past that no longer exists due to the success of modern vaccines may help prevent us from having to experience that past once again.

TheEvidenceDoc 2016

If you want to learn more about the vaccinations available to prevent disease in adults, check out the resources available from the CDC.


A Powerball® ticket and relative vs absolute estimates of disease

This week's Powerball® mania seems a good time to talk about relative and absolute estimates of disease. This epi professor learned from her students years ago (especially from a bartender and professional gambler) that real world examples can be useful to explain epidemiology and biostatistic methods.

Got yours?

Got yours?

Do you have a lottery ticket for Saturday's draw? I'll admit to an occasional purchase when the payout is high, just for the entertainment value of having a ticket in hand in the company of friends as the numbers are called out. But only the one set of numbers. For after all, my absolute risk of winning the big payout, according to Powerball® is just 1 in 175,223,510 or 0.000000005707. If I buy 10 tickets, it's now just 10 in 175,223,510 or 0.00000005707, a barely detectable increase.  But according to news reports, that doesn't stop people from buying 1,000 or more tickets to increase their chance of winning.

This lottery ticket example provides an easy example of how changing my relative odds or relative chance of winning - a ten fold increase by buying 10 instead of 1 ticket - doesn't really change my absolute chance of winning by any appreciable amount because the underlying chance of winning is such a rare event.

So why are epidemiologists like me so enamored with relative disease estimates and seemingly less enamored with absolute disease estimates?

These different measurements serve different purposes.

Relative Disease Estimates

One of the big goals of epidemiology is to study patterns of disease and health and in so doing, to discover associations that may be causal relationships. So we do research like the studies of Sir Richard Doll that uncovered cigarette smoking as a cause of lung cancer, at a time when the suspected major cause was believed to be industrial pollution.  Or like the research that uncovered occupational exposure to vinyl chloride as a cause of angiosarcoma of the liver.  These kinds of studies compare the occurrence of disease in persons with exposure to those without. Through these relative comparisons, epidemiologists demonstrate 1)strength of association by comparing exposed to unexposed people and 2)dose response by measuring increasing occurrence of disease in persons with increasing levels of exposure. These represent two of HIll's causal criteria, with Hill's Causal Criteria being one of the logic frameworks for assessing causality. We'll talk more about Hill in context in a later blog. For now, we are simply explaining the relative importance of relative measures in an epidemiologist's armamentarium.  Epidemiologists like to discover causal relationships, after all, Sir Richard Doll is famous, well, at least among us epidemiologists.

Of course, it's pretty obvious that having a ticket is causally related to winning. Your odds of winning with no ticket are zero. But there isn't a dose response; the person with the most tickets isn't guaranteed to win it.

So a causal path, or analytic framework for winning the lottery is having at least one ticket.

Absolute disease estimates

Absolute estimates provide an assessment of the frequency of a disease or condition in a population.  Absolute estimates are an important tool for health policy and planning when determining where to place limited resources.  Likewise, they should be used by people with limited resources when deciding how many tickets to buy or even whether to play the lottery.

Your doctor will balance information from relative and absolute estimates, which is important in direct patient care, particularly in shared decision making when there are care choices. We'll need to spend a whole blog on that topic. But our goal for now is to start with a clear picture of the difference between relative and absolute estimates.  Got it?

TheEvidenceDoc May 2013