Current vaccines target the hemagglutinin, the antigen most exposed to the immune system (see 103–104), which looks something like the head on broccoli. Unfortunately, the vaccines target the head portion, which mutates rapidly and is a part of the virus that can change without interfering with the functioning of the virus. That’s part of the reason influenza vaccines are not particularly good: between 2003 and 2017 their effectiveness ranged only from 10 percent to 61 percent. (Even at those levels, they prevent millions of cases and thousands of deaths and are well worth getting.) For the
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