On February 21, 2008, a special advisory panel convened by the U.S. Food and Drug Administration met in Gaithersburg, Maryland, to select the three influenza virus strains to be included in the influenza vaccine for the 2008—9 U.S. flu season. It is not a decision panel members took lightly. According to the Centers for Disease Control and Prevention (CDC), between 5 percent and 20 percent of the population gets the flu each year, more than 200,000 people are hospitalized, and about 36,000 people die.
Their decision was the culmination of a global effort, orchestrated by the World Health Organization, to monitor changes in the flu viruses currently attacking people. This information is collected at 122 national influenza centers in 94 countries, which is then sent to four WHO collaborating centers including the CDC in Atlanta and three other comparable organizations in London, Melbourne, and Tokyo. Based on this research, experts forecast which viruses are likely to circulate the following season.
Flu viruses are notorious for mutating rapidly, but the current process of manufacturing the flu vaccine, which takes five to eight months, requires scientists to make an educated guess about the composition of the projected vaccine well before the onset of flu season. Flu vaccines are prepared using specially fertilized chicken eggs. The influenza virus is injected into the fluid surrounding the embryo, where it multiplies. It is then harvested, purified, and used to produce the vaccine. This is a time-consuming process. The eggs have to be taken from flocks that are certified disease free, and then they have to be cleaned and sterilized.
There are other drawbacks to this approach. People who are allergic to eggs can't take advantage of vaccines made this way. If there were a flu pandemic such as the one we experienced in 1918 and everyone in the United States had to be vaccinated, vaccine makers would require 900 million eggs. It just can't be done.
In 2006, the federal government awarded more than $1 billion in contracts to five vaccine makers to develop a more efficient and faster way of manufacturing flu vaccines. These companies are exploring growing their flu virus in cell lines developed from humans, monkeys, and dogs, a process that could shave weeks off the production process. Because large volumes of these cells can be grown in advance and placed in freezers, they would be available in the case of a pandemic. Such methods are already being used to produce polio and smallpox vaccines.
In the meantime, the current system is working more efficiently than it did for the 2004—5 flu season, when a plant in England slated to produce 48 million doses of flu vaccine was closed by British health officials. Vaccine manufacturers are projecting that as many as 143 million to 146 million doses will be available for the 2008—9 influenza season. This is an all-time-high supply of vaccine. Shipments began in August.
When timing your flu shot, there are two things to keep in mind. Immunity provided by the vaccine develops in 14 days and lasts about a year. Getting your flu shot early and avoiding the crowds is consequently a good strategy. But if December or even January rolls around and you still haven't gotten vaccinated, a flu shot can still help. In most years, influenza doesn't peak until January, February, or later.
The CDC estimates that for seniors over 65 living independently, the flu vaccine is between 30 percent and 70 percent effective in preventing hospitalization for influenza and for pneumonia, a common complication. The bottom line: you have everything to gain from getting a flu shot and nothing to lose—and while you're at it, check with your physician to make sure your pneumonia vaccination is up to date.