Q: Last week I saw an advertisement for getting flu shot at a local pharmacy chain. It was only the first week of September, but they were already offering flu shots. Is that the best time to get vaccinated against the flu?
The peak flu season in the United States runs from October through March, with most infections occurring in February. After getting a flu shot it takes about 2 weeks to become fully effective and gives you the best protection for the next 12 weeks, after which your flu protection slowly decreases. Will one flu shot last you an entire flu season, even if you get it in September? If you are young and healthy, the answer is yes; one shot will provide you with good protection for the entire flu season.
Unfortunately, older Americans do not get as much protection against the flu from flu shots. The Center for Disease Control (CDC) recommends getting a flu shot anytime after the vaccine becomes available because they don’t want to miss any opportunity for most Americans to get vaccinated. But if you are over 60 and it’s convenient for you, it might be better to wait and get your shot a little later to match up your 12 weeks of best protection from the vaccine with the peak month of illness from influenza, which is typically in February.
If you are over 65, it’s especially important you get a flu shot. Every year between 5-20% of Americans become ill with influenza. Those age 65 and older have an increased risk of serious complications from influenza such as pneumonia, dehydration and worsening of chronic conditions such as lung disease, congestive heart failure and diabetes. 90% of the deaths associated with influenza occur in the over-65 age group.
One of the biggest challenges to preventing deaths from influenza is just keeping up with it. Measles, mumps, and chicken pox viruses have stayed pretty much the same over the decades we’ve had vaccines against them. Not so with influenza; it keeps changing its shape, making it harder for our immune system to detect and respond to. The World Health Organization (WHO) keeps track of influenza patterns across the world with centers in Tokyo, Beijing, Melbourne, London and Atlanta.
Most new types or strains of influenza start in China, where farmers live among the animals they raise. Various influenza strains infect geese, chickens, ducks, pigs and humans, sometimes without any outward signs of illness. While inside its host, the virus reproduces itself millions of times. Small errors can occur during the replication process and instead of an exact copy the virus may end up slightly different. If the new version proves to be better at causing disease than the original strain, it replaces it, introducing a more powerful strain into the world.
If two different strains infect the same host, it’s possible for them to come in contact with each other as they reproduce. If part of one strain accidently swaps part of itself with another strain instead of with itself, a “new” influenza strain is created. Most scientists believe the next pandemic will be from an influenza virus that was accidentally transformed like this.
Most human influenza is caused by 2 strains, called A and B. The A strain causes more severe symptoms and is associated with pandemics. The particular strains chosen for each season’s flu vaccine are selected because they are most likely to infect you, to cause you serious illness and can be grown into a commercial vaccine in time for flu season. Traditionally, influenza vaccines have had 3 strains and are called trivalent: two A strains and one B strain but starting last year there are vaccines with 4 strains, two each of A and B.
Influenza vaccine has been traditionally grown in eggs, but some of this year’s vaccine was produced using newer techniques. Flublok® uses recombinant technology to grow influenza virus completely without eggs and is safe for people who have a severe egg allergy. Another vaccine is grown in cell culture, which is exciting because it produced vaccine more rapidly than the traditional way. Having more rapid methods for producing influenza virus would be of great value during influenza pandemic.
There were no new strains of influenza circulating this past year, so this fall’s flu vaccine is the same formula as the ones used last year. Because your protection from last year’s vaccination has faded, be sure to get another flu shot. There’s more for you about the flu at http://www.cdc.gov/flu/keyfacts.htm.
