One of the biggest problems in trying to convince people that they need to immunize against things like the flu is that they don’t really feel the pressure. After all, for most people, the flu shot is an inconvenience, and they’re unlikely to get the flu in a given year. So why bother? Quite a few readers expressed this view after my article “Why It’s Still Worth Getting a Flu Shot” on Thursday, including this one.

I promise this is an honest question: Are people routinely being destroyed by the flu or something? (I mean, first I’d ask, ‘Is everyone but me simply vaccinated, and thus gifting me with herd immunity?’ And so I did. My first Google search brought me to yearly C.D.C. flu-vaccine coverage statistics, and for the last four years, the percentage of flu-vaccinated adults has been in the low 40s. So... nope.) I’m not a particularly healthy person — I get colds, sinus infections, etc. — but I just can’t recall ever having had the flu, or at least *knowing* I had it. This seems to indicate that the flu is either 1) rare enough that it’s possible for me to have been lucky forever (in which case it’s fairly rare, apparently), or 2) not severe enough of an illness for me to have noticed experiencing it. Both lead me to conclude that skipping the vaccine is fine. I’m just a regular idiot, presumably representing other regular idiots, amenable to changing their habits, but who haven’t done so — not due to obstinance or contrarianism, but due to signals so mixed as to inspire ambivalence — and if this article can be said to have provided the ‘why’ its headline promises, unfortunately it hasn’t provided the ‘why’ idiots like me need to hear: Why is the flu a big deal literally at all? — Chrystie, Los Angeles

Although I devote some of my articles to telling you not to worry so much about some diseases or other risks, influenza is one thing you actually should worry about. It’s terrible; it’s also far too common.

Influenza, commonly called the flu, spreads easily. You can catch it from someone who coughs, sneezes or even talks to you from up to six feet away. You can infect others a day before you show any symptoms, and up to a week after becoming sick. Children can pass along the virus for even longer than that.

Influenza is not a reportable disease, so its prevalence must be estimated. The Centers for Disease Control and Prevention believes that, since 2010, between 9.2 million and 35.6 million people have come down with the flu in the United States each year. That means that in a bad year, more than one in every 10 people in the United States might get it.