An excellent essay by Carl Zimmer: Curing our Influenza Amnesia.
Our brains are not the only places where we can store memories. Each time a new pathogen invades our bodies, our immune cells have an opportunity to recognize it by some feature, usually some distinctive cleft or spike of a protein on its surface.
After our bodies defeat the infection, some immune cells are tasked with keeping the memory of that feature alive for years. If that same pathogen returns for a second attack, our bodies can launch a far faster counterattack. We can tutor our immune systems with vaccines. Depending on the disease they protect against, vaccines may contain dead viruses, protein fragments, or some other substance derived from a pathogen. Our bodies then make antibodies against those substances, and some immune cells continue making those antibodies for years. For many diseases, our memories can endure like etchings in stone. Once children get shots for polio, they’re usually protected for the rest of their lives.
Unfortunately, the same can’t be said for the flu virus. When it comes to influenza, it’s as if we have short-term amnesia. Time and again, studies have demonstrated that flu vaccines are effective—but usually only for a single flu season. When the next flu season arrives, the viruses have changed, and we have little protection from the year before. We have to teach our immune systems yet another lesson.
Carl Zimmer is the author of several books. Buy his latest book, A Planet of Viruses, now!