A few years ago, traveling in Jerusalem, I picked up a terrible souvenir: the flu. Rather than visiting important landmarks, I went sightseeing in the hospital emergency room. An important lesson came from that trip: always get a flu shot.

Influenza, more commonly known as the flu, seems like normal inconvenience to most healthy adults but it can be deadly. If you are infected and cough or sneeze, you can spread the flu to anyone within six feet. Once contagious, you will likely pass the virus to one or two other people. This is important because very young children, pregnant women, elderly adults, and anyone with a chronic illness such as asthma (nearly 10 percent of the population), heart disease, or kidney disorders, among others, are at a higher risk of serious complications. Roughly 5-20% of the U.S. population will get the flu in any one year, and well over 100,000 of them will end up in the hospital. Between 3,000 and 49,000 Americans, most of them elderly, die from flu-related causes every year, depending on the severity of the season.

There are a few differences between the flu and a run of the mill cold.  The flu tends to strike suddenly, while a cold's symptoms progress day by day. Telltale signs of the flu can include fever, headaches, fatigue and muscle aches, and chills. These are generally more severe than with a cold, and a cold is more likely to come with a runny nose. A cold is annoying—the flu makes you miserable.

Philadelphia offers flu shots at its community health centers, federally qualified health centers, and at dozens of community flu clinics, listed here. The flu shots are available to city residents and are free for those without insurance.

Some health departments in suburban counties also offer flu vaccine for residents. The Healthmap Vaccine Finder can help locate pharmacies, supermarkets, and other places that offer flu shots; they will charge a fee but may accept health insurance. Your primary care doctor likely offers the vaccine as well.

There are six options, some of them new this year:

  • Regular flu shot. This "trivalent" vaccine protects against the three strains of the virus that are expected to be most common and is recommended for everyone over the age of six months.
  • Quadrivalent flu shot. It This vaccine protects against the same three strains (an A/H1N1, A/H3N2, and a Type B) plus a fourth (another B).If you want really detailed information, click here.  It is recommended for everyone over the age of six months. This is the only shot that protects against four strains. There also  is a quadrivalent  nasal spray vaccine, the only nasal version this year. It  is recommended for people ages 2-49 – a smaller range than the shot – who are healthy and do not want to be stuck with a needle.
  • High dose flu shot. This contains a higher amount of the antigen (immune system stimulant) needed to create immunity. It is recommended for adults over 65 because the immune system weakens with age.
  • Intradermal (inside the skin) flu shot. This vaccine creates the same immune response but uses a much smaller needle.
  • Flublok flu shot. This is created without using chicken eggs and is suitable for adults aged 18-49 who are allergic to eggs. It protects against three types of flu.
  • Flucelvax flu shot. This vaccine is made using cultured animal cells, so it, too, is  appropriate for people egg allergies. If there is ever a flu pandemic, using cell cultures will allow  vaccines to be made more quickly.

Often, people are reluctant to get the vaccine because they fear it will give them the flu. It can't (although some people do come down with the flu soon after getting a shot, just as they would have without it). The vaccine in flu shots is made from dead virus, and the nasal spray is made from a weakened virus that cannot survive inside the body. Here are some other myths about the vaccine.

The flu vaccine is far from a guarantee. Last year's reduced the likelihood that healthy, non-elderly people will need to see a doctor for symptoms by 60% – better odds than medicines for various diseases provide. Still, it is less effective than, say, the measles-mumps-rubella (MMR) vaccine that creates immunity to all three viruses in 95% of people given one dose and the chickenpox (varicella) vaccine, which is 80-90% effective.

Two types of flu cause seasonal outbreaks: Type A and Type B. (There’s also Type C, but it causes only mild illness.) There are subgroups, commonly known as strains, and the variation is most pronounced within Type A, which typically strikes earlier in the season and causes more illness than Type B. Flu viruses are constantly changing, which is why there is a new vaccine every year. It also means that the vaccine is not always a perfect “match” to the virus – predicting which strains will dominate, based on those that are emerging on the other side of the world, far enough in advance of our flu season so that vaccine can be created, tested, and mass produced, is a form of scientific guesswork. Even an imprecise match, however, can give you a much better chance of avoiding the flu and, if you do get sick, may help lessen your symptoms because there is overlap among the strains.

Every once in a while – four times in the last century – the flu virus changes so dramatically that few people have the partial immunity that they developed from exposure to related strains in previous years. That's called a pandemic, as in the Type A H1N1 pandemic of 2009. Once a large percentage of the population developed immunity to that strain, through a combination of vaccination and infection, it no longer had pandemic potential, and its successors have been among the seasonal flu strains for the past few years.

Even the seasonal flu is serious, and we're fortunate to have a vaccine that can help keep us healthy. Do yourself (and everyone you know) a favor and get a flu shot. I will.

Teagan Keating is a second year master's student at Drexel's School of Public Health. Find her on Twitter.

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