The efficacy of the flu vaccine in the 2017-2018 season was less than ideal, about 40 percent. This means that with the vaccination you were about 40 percent less likely to get the flu than without. The problem comes from nature of the Influenza virus itself. The virus is what is known as an RNA virus, when it reproduces it is likely to reproduce somewhat incorrectly. This makes matching the vaccine to the virus more difficult. Regardless, even with those low odds, you’re better off getting the shot and hopefully the vaccine will better match the virus this year.
Don’t be misled by anti-vaccination groups. They list scary sounding ingredients and list possible risks if exposed to millions of times higher doses than are present in a vaccine. An example is formaldehyde, present in many vaccines in trace amounts. In large doses it can be toxic, but not in the amounts present in vaccines. It is actually a component of natural metabolic processes in the body. If you want to talk about a dose, one bite from a pear contains many times as much formaldehyde than a slew of vaccinations. Don’t worry about exposures to trace amounts of ingredients.
The effectiveness of vaccinations depends on so-called herd immunity. To stop a communicable disease does not require absolutely everybody is vaccinated, just a high enough percentage to disrupt transmission. Some individuals can’t be vaccinated for certain diseases such as neonates for pertussis or because of severe immune reactions to proteins present in the vaccine. They are protected from disease by virtue of the fact that those around them have been vaccinated and therefore don’t carry the disease.
A real problem with getting a vaccination is a misperception of risk. A person may know of someone who got a flu shot, and had a bad reaction or had the shot and still got the flu. This knowledge introduces bias. It doesn’t however change the fact the overwhelming odds are in favor of getting the shot. Depending on the vaccine, the strain of influenza, and several host factors, “ … recent studies have supported the conclusion that the flu vaccination benefits public health, especially when the flu vaccine is well matched to circulating flu viruses” – Centers for Disease Control statement. The odds of a severe negative outcome, usually due to an allergic reaction to the vaccine are in the one to millions range.
Back to the bias of knowing someone for which a flu shot didn’t work, or had a reaction. Does knowing someone who won the lottery make you more likely to win the lottery? Most folks would say of course not. But this is the same kind of bias. You think of just one outcome among many. That doesn’t change your odds.
We all know someone who doesn’t wear a seat belt. S/he frequently justifies the self-endangerment by claiming that they know of a case where someone died due to the seat belt. The same bias. Evidence from literally billions of passenger miles shows seat belts save lives.
Vaccinations are generally safe and efficacious. Vaccinations protect not only those vaccinated but also others who can’t through the herd immunity. Participate in society, get the shot.