Introduction
In some ways, the flu vaccine is an optional vaccine because it is not required for any school admission or work attendance. Consequently, only a small percentage of the population typically gets vaccinated each year. Due to the low vaccination rate, the vaccine manufacturers do not even make enough vaccine each year for every vaccine-eligible person. During the year when vaccine shortage is not an issue, millions of doses of the flu vaccine are routinely destroyed because they are unused by the end of the flu season.
The reason why last year's flu vaccine is no good for the current year is that each year the types of flu virus that circulate are different from the year before. This is the reason why people may catch the flu year after year if they are not vaccinated.
The flu virus is very tricky. Different strains of the virus take turns in causing outbreaks each winter, so even if everyone's immune system remembers the virus that caused the flu from years ago, a different strain can still sneak past your immune defenses and wreak havoc on your body.
Since the flu vaccine cannot be given to everyone, how do you know whether you or your child needs the flu vaccine?
The flu vaccine is especially recommended for children less than 18 years old (but older than six months) and for adults older than 50. In addition, people with asthma, heart problems, or weakened immune systems should get vaccinated. Household members of those who are at risk should be immunized as well.
The constantly changing nature of the flu virus is also the reason why a new flu vaccine must be made each year. Last year's flu vaccine would not work very well for the current flu season. On June 30 of each year, the leftover flu vaccines from the year before are all destroyed so a new batch can be made for the following flu season. This also means that if you got the flu shot last year, you'll have to get it again this year to stay protected.
Essential
It takes the flu vaccine two weeks to get your immune system ready to fight off the flu virus. This means that if you received the flu vaccine two weeks ago, you can still catch the flu until two weeks after the shot. This is why you need to get vaccinated as early as possible in the flu season.
The changing flu virus also makes the production of the flu vaccine very challenging. In order to make the vaccine that works for each particular flu season, scientists must predict before the flu season starts which strains of the flu virus will cause outbreaks. Scientists and doctors can make educated guesses from patterns of previous flu outbreaks and trends of infection from years before. Nevertheless, the prediction is not always perfect. If the scientists guess incorrectly, the flu vaccine will not work as well.
Fact
In 2003, the flu vaccine manufacturer Wyeth had to destroy more than 6 million doses of the flu vaccine because of weak demand. The company lost more than $30 million that year and was forced out of the flu vaccine business for the following year. A massive vaccine shortage ensued in 2004.
You may wonder why scientists cannot wait until the beginning of the flu season to see which flu strains are circulating before making the flu vaccine. The problem is that it takes six months to produce the flu vaccine. If scientists wait until the beginning of the flu season to make the vaccines, by the time the vaccines are made available, the flu season would be over. The vaccine would be quite useless by then.
Fortunately, each flu vaccine is able to protect against three flu strains. So even if scientists guess wrong on two out of three strains, the vaccine would still protect some individuals from getting sick. In a good year, the flu vaccine works perfectly because the scientists predict all three of the flu strains that are responsible for the flu season.
The difficult process of making the flu vaccine is also the reason why there were massive vaccine shortages in the past. Vaccine-making companies usually have to write off huge financial losses each year because of weak demand for the vaccine and the mandatory destruction of a large number of the vaccines at the end of the flu season. Consequently, many companies simply stopped making the flu vaccine.
Due to these various limitations of the flu vaccine, scientists are working hard at inventing a flu vaccine that works for all strains of the flu virus. Once this all-purpose flu vaccine becomes available in the future, throwing away unused vaccines will not be necessary anymore.
Can pregnant women get the flu shot during the first trimester of pregnancy?
The injectable form of the flu vaccine (the vaccine that contains killed flu virus) is safe for pregnant women. In fact, a 2008 study published in the New England Journal of Medicine demonstrated that babies born to mothers who had the flu shot during pregnancy get sick less often.
There are two types of the flu vaccine. The injectable form of the vaccine is approved for children older than six months, and the nasal spray flu vaccine (trade name FluMist) is approved for children older than two years of age.
Children less than nine years old getting the flu vaccine for the first time in their lives need to receive two doses of the vaccine to be fully protected. The two doses of the flu vaccine need to be separated by least four weeks.
