It used to only happen when your immune system fell below a certain level: as you age, you lose your immunological memory and you can get shingles. But in recent years we’ve seen a massive shift in the age of people getting shingles. It used to be mostly people in their 70s or older. Now it’s hitting people in their 30s. And people started to say, well, that’s weird, what’s going on?
Yeah — what is going on?
We used to think we just had this spectacular immune response when we first encountered the virus at, say, age 6, and that the immune response lasted until we were 70. But actually what we were seeing was the effect of an immune system being retrained every time it came into contact with the virus after the initial infection — at 6, and 7, and 8, and so on. Every time your friend got chickenpox, or your neighbor, you got a massive boost. You were re-upping your immune response and diversifying your immunological tools — potentially multiple times a year, a kind of natural booster.
But now, in America, kids get chickenpox vaccines. So you don’t have kids in America getting chickenpox today, and never will. But that means that older Americans, who did get it as kids, are not being exposed again — certainly not multiple times each year. And it turns out that, in the absence of routine re-exposures, that first exposure alone isn’t nearly as good at driving lifelong immunity and warding off shingles until you immune system begins to fall apart in old age — it can last until you’re in your 30s, for example but not until your 70s.