Not only is influenza really unpleasant acutely, it can last for over a week, and then cause a sinus infection that can take weeks to clear or a cough that can persist for months. It can even kill people, either through weakening their systems or from direct effects, such as infecting the brain, causing severe life threatening viral pneumonia or even heart problems. Each year 30-40 thousand people die of direct effects of the flu, which is a huge loss of life and mostly underappreciated. Most of those who die of the flu are very young or very old or weakened by disease, but not all. Some healthy people get the flu and die. In the influenza epidemic of 1917, 50-100 million people died over 3 years it lasted, and they were primarily young and not otherwise ill. Some years, however, flu outbreaks are pretty minimal.
The influenza vaccine has existed since the 1940s, and has been tested extensively since then. Each year now the vaccine is created anew, based on the predicted viruses identities for the next year. Vaccine side effects are usually quite mild, though causing the body to create disease fighting antibodies is sometimes associated with a vaguely ill feeling. People do not get the flu, per se, from the flu shot, though they might become ill in the doctors office while waiting to be vaccinated by being around other coughing and sneezing patients. In 1976 a vaccination aimed at preventing swine flu ended up causing a severe nerve disorder called Guillain Barre syndrome in 1 of 100,000 people who received the shot. Guillain Barre can also happen in a person due to any actual infection, including influenza itself.
Being vaccinated results in a rise in the antibodies that protect against the particular variety of the flu that the vaccine was designed to prevent. In many studies of flu shot effectiveness it has been shown that people who get vaccinated are less likely to go to the hospital, get pneumonia or die. During an influenza outbreak, usually about 1 in 10 people under the age of 19 become infected and it is possible to judge the presence of flu in a community by large numbers of students being absent from school. Vaccinated healthy people are less likely to miss work during flu season and vaccinated elderly people have a 68% reduction in death during flu season. Some of this effect may be due to the fact that healthier and more affluent elderly people are more likely to be vaccinated than the poor and homebound, but this does not entirely explain the effect. Healthy vaccine recipients are significantly more likely to have good immune response to the vaccine than elderly or very young or otherwise medically vulnerable people, so their protection from the virus is probably correspondingly higher. Some years vaccine designers guess wrong about which influenza virus will be the most prevalent and so there have been years when the vaccine was all but useless. Production of enough antibody after vaccination to protect against flu varies significantly for different subgroups of people, from as low as 20-30% in older adults and as high as over 60% in healthy volunteers. The fact that the only a small proportion of the elderly respond to flu vaccines in any measurable way, and yet their death rate during the flu season is profoundly reduced does bring into question whether getting the flu shot is merely a marker of good health rather than protecting against disease.
Each year about 100million people receive the flu shot in the US. Some much smaller number of people are vaccinated by the nasal route, receiving, instead of an inactivated vaccine, a live virus that infects the body without causing harm, thus raising the flu related antibodies more naturally. Evidence suggests that this route of vaccination may be more effective in children, but recent studies have overall shown more influenza type disease in recipients of the live vaccine. The more common, inactivated flu vaccine is given as a shot in the upper arm, into the muscle. It can cause aching that may last a few days, and occasionally causes significant swelling. Two years ago when there was a vaccine shortage information was released showing that injection just under the skin into the subcutaneous tissue of 1/5th of the volume of a standard flu shot was at least as effective as the intramuscular injection. It was suggested that physicians might be able to give more shots to more people with less vaccine if they did the vaccination this way. This year, as an experiment, I vaccinated myself and my family with a smaller than standard dose of flu vaccine subcutaneously. We all felt that it stung a little bit more, but didn't ache as deeply as the intramuscular route but was otherwise a little bit superior due to the shorter and tinier needle that is usually used for that type of injection. I have been curious, for the last two years, about why a subcutaneous injection of the flu vaccine had not become standard of care if it works better and utilizes fewer resources. Vaccines are very big business, though I'm not sure exactly what the numbers are. The biggest manufacturers of influenza vaccine are Sanofi Pasteur and Glaxo Smith Kline. If they make even 2 dollars per shot, which is probably a low estimate, the profits would be $200 million dollars in the US alone. If influenza shots were given subcutaneously, the world could get by with 1/5th the amount of vaccine, significantly reducing profits. But I just read in the Medical Letter today that Sanofi Pasteur has figured out how to avoid that pitfall of cost savings by producing a single dose subcutaneous injection of flu vaccine for...only $4 more per dose than their standard flu vaccine which costs the pharmacist or physician $12! Clever Sanofi Pasteur. If we physicians are not mindless sheep, however, we will figure out that we can start giving 1/5th size subcutaneous flu shots with tiny little needles in the not to distant future.
So--bottom line--should you get a flu shot? Probably yes. If you are healthy, your antibody response will be robust and you will be less likely to get the flu this year, miss work, feel terrible and possibly (but not likely) die. If you are very old or infirm, your immune response will be less but your downside should you get sick is significantly higher, and might more reasonably include dying. It also seems clear that more research is needed to define exactly who will benefit from flu shots, and that the ethics of withholding flu shots from a random group of people in order to do good science is complex. If it turns out that flu shots really don't protect well from death and disease, we are wasting a colossal amount of resources in vaccinating everybody as we are now.
What is the very best way to prevent the flu? Probably by avoiding exposure to sick people by having more comprehensive policies to discourage sick people from going to work and school. This will never be perfectly effective due to the fact that people can be significantly contagious before they get sick enough to realize that they need to be home. That said, I do wonder if even this approach is optimal. It may be that frequent exposure to germs in levels insufficient to cause actual disease might serve to immunize those exposed and make them less likely to catch or spread the disease in the future.
Flu shots are available to anyone at a cost of about $25 a pop at grocery stores and pharmacies and are covered by virtually all insurance companies. They are usually offered to patients starting in late September commercially, but since immunity only lasts for 3-4 months and outbreaks frequently occur after January, waiting to get the vaccine until the end of October is recommended. In the US flu vaccine is recommended for all people over the age of 6 months, including pregnant mothers. It is particularly recommended for healthcare workers who are more often exposed and who have a higher likelihood of spreading the disease to vulnerable populations.