Getting the influenza vaccine is the most effective way to reduce the chance of becoming infected with the flu. People who get the influenza vaccine have a lower chance of illness and death from influenza compared to people who are not vaccinated.
Vaccine Timing
Because the influenza virus changes (or "mutates") slightly from year to year, you need a new influenza vaccine before each flu season. People should get the flu vaccine as soon as it is available to get the most benefit.
In the northern hemisphere, the flu season usually occurs between November and April. In the southern hemisphere, the flu season usually occurs between May and October. Flu can occur at any time of year in the tropics.
In the northern hemisphere, the flu season usually occurs between November and April. In the southern hemisphere, the flu season usually occurs between May and October. Flu can occur at any time of year in the tropics.
Vaccine Effectiveness
People who are vaccinated form antibodies (proteins), which destroy the influenza virus after the person is exposed. It generally takes about two weeks to make these antibodies. The vaccine usually protects 50 to 80 percent of those who are vaccinated from getting the flu.
If you get the flu after being vaccinated, your symptoms are likely to be milder and last for a shorter time compared to people who were not vaccinated.
If you get the flu after being vaccinated, your symptoms are likely to be milder and last for a shorter time compared to people who were not vaccinated.
Injection versus nasal spray
The flu vaccine is available in two forms in the United States, as an injection and a nasal spray.
- The injection is approved for adults and children 6 months and older.
- The nasal spray is approved only for healthy children age 2 years and older and healthy adults up to 49 years.
Pregnant women and people who have a weakened immune system or who have chronic medical problems should not get the nasal spray since it contains live virus. If you live with a person with a severely weakened immune system, you should not get the nasal spray.
Vaccine side effects
The most common side effect of the flu shot is soreness at the injection site.
People with a serious allergy to egg products should talk with their doctor or nurse before getting the nasal spray or shot because both are prepared from viruses grown in eggs.
People with a serious allergy to egg products should talk with their doctor or nurse before getting the nasal spray or shot because both are prepared from viruses grown in eggs.
Other possible side effects of these vaccines include body aches, headache, and a low-grade fever (usually less than 100.4ºF or 38ºC). These problems are usually mild and go away within a day or two.
Many people are concerned about the safety of vaccines. But for most people the risk of complications from the vaccine is much smaller than the risk of complications from being infected with the flu. While no vaccine is 100 percent safe for everyone, the flu vaccine appears to be low-risk. For example:
Many people are concerned about the safety of vaccines. But for most people the risk of complications from the vaccine is much smaller than the risk of complications from being infected with the flu. While no vaccine is 100 percent safe for everyone, the flu vaccine appears to be low-risk. For example:
- The flu vaccine is less likely than the flu itself to increase the risk of a nervous system disorder called Guillain-Barré syndrome.
- There is no evidence that the flu vaccine increases the risk of birth defects or miscarriage.
- Some formulations of the flu vaccine contain a preservative called thimerosal, which is derived from mercury. However, there is no convincing evidence that the small amount of thimerosal in this vaccine will be harmful to children, pregnant women, or adults.
- Several groups, including the Vaccine Adverse Event Report System (VAERS, http://vaers.hhs.gov), monitor the reports of vaccine side effects closely.
Who should be vaccinated?
- Adults age 50 or older.
- People who live in nursing homes and other long-term care facilities.
- Adults and children who have chronic lung or heart conditions. This includes children with asthma.Adults and children with chronic diseases such as diabetes or kidney disease.
- Adults and children with HIV infection, or who have received organ or stem cell transplants.
- Children and teenagers age 6 months to 18 years who are taking long-term aspirin therapy and might be at risk for Reye syndrome.
- Women who will be pregnant during the influenza season.
- Adults and children who might transmit influenza to high-risk individuals (including people listed above). This includes healthcare workers, workers in nursing homes, home health workers, and people who live with a high-risk individual.
