Public health officials repeatedly advise most everyone 6 months and older to take a flu shot, yet many don’t. Sometimes that’s because the science behind a flu shot can be difficult to understand. Thursday we addressed why flu is worse in the winter and how shots are made. Today we’ll dive into the details of how the vaccine works to keep people from getting the flu.
Understanding the strains
There are three types of the flu: A, B and C. Type C is less severe and not included in the vaccine.
Type A viruses, the most severe, have proteins on their surface that they use to infiltrate human cells. There are 16 different possible H proteins and nine N proteins. So it starts with H1N1, H1N2, H1, N3 and so on for 144 different combinations up to H16N9. But the problem with the flu virus is it constantly mutates, creating differences within a strain and sometimes two strains crossing together.
A vaccine typically contains three strains — two As and one B — that the World Health Organization believes at the beginning of the year will be most common. Typically, as it did this flu season, for the Type A flus the WHO picks a type of H1N1 (known as swine flu) and a type of H3N2. This year the H3N2 seems to be more prominent, and unfortunately it tends to be the more deadly strain, perhaps because it’s harder to vaccinate against because it mutates quickly.
What vaccines do
Our bodies naturally fight flu viruses using antibodies. They are proteins that latch onto a flu virus and can either fight it directly or leave a marker telling other parts of the immune system to fight it.
When you get the flu shot, three inactivated (think dead) strains are put into your body, which naturally starts developing antibodies to fight them. Only there’s nothing to fight against with the inactivated strain. But if you actually get that strain into your body in the real world, you’ll have built up antibodies against it. That can mean you either don’t get the flu at all — all of the virus is killed before it causes any effect on your health — or it is less severe than it would have been because your body’s immune system is able to win the war faster.
How effective are vaccines
In short, it depends on whether the vaccine strains in the flu shot match up with the strains circulating where you live. It also seems to depend on whether you get H1N1 or H3N2.
A 2016 study in the scientific journal The Lancet looked at all the studies of flu effectiveness it could find done between 2004 and 2015. It found when H3N2 was the dominant strain in a year that getting a flu shot reduced your risk of getting the flu by 33 percent. It was more effective if H1N1 or a B strain was dominant.
Think of it this way: If someone pointed a six-shooter at you with four bullets loaded, would you want them to remove one of the bullets? Of course you would. Why? Because it would reduce your chances of getting shot by 33 percent. If they pulled the trigger, would there still be a chance that you would get shot? Again, of course, but removing the bullet was still the smart choice. n
— Charlie Smith
