Flu (Influenza)

Each year, the seasonal flu vaccine protects against the three influenza viruses that research suggests will be most common during that season. While some manufacturers are planning to produce a four-component vaccine in the future, they will not be available for the 2012-2013 flu season.

There are two types of flu vaccines: the flu shot, made from killed flu virus and given with a needle; and the nasal-spray flu vaccine, made from live, weakened flu virus.

A nurse delivers a seasonal influenza vaccine. Credit: CDC

Currently, three seasonal flu shots are being produced for the United States market:

• The regular seasonal flu shot, which makes up the bulk of the vaccine supply in the U.S. This shot is intramuscular, which means it is injected into muscle (usually in the upper arm). It has been used for decades and is approved for use in people ages six months or older, including healthy people, people with chronic medical conditions, and pregnant women.
• The high-dose vaccine for people age 65 and older, which is also intramuscular.
• The intradermal vaccine for people age 18 to 64, which is injected into the skin. This vaccine was first made available during the 2011-2012 flu season.

Vaccination with the nasal-spray flu vaccine is an option for healthy, non-pregnant people age 2 to 49. The exception is healthcare workers who care for people with severely weakened immune systems who require a protected hospital environment; these people should get the flu shot instead of the nasal-spray vaccine.

Everyone age six months and older should get the seasonal flu vaccine every year. Vaccination is especially important for people who are in close contact with groups at high risk of flu complications, or are at high risk themselves. These groups include

• Pregnant women
• People with certain medical conditions, including asthma, diabetes, and chronic lung disease
• People age 65 or older
• People who live in nursing homes and other long-term care facilities
• People who live with or care for those at high risk for complications from flu, including
  • Healthcare workers
  • Household contacts of people who have asthma, diabetes, and chronic lung disease
  • Household contacts and caregivers of children under age five, especially contacts of children younger than six months of age

If you have questions about whether you should get a flu vaccine, talk to your healthcare provider.

Some people should not be vaccinated without first consulting a healthcare provider. They include

• People who have a severe allergy to chicken eggs
• People who have had a severe reaction to flu vaccination in the past
• Children younger than six months of age
• People with a history of Guillain-Barré Syndrome, a severe paralytic illness, that occurred after receiving the flu vaccine and who are not at risk for severe illness from influenza

People who have a moderate or severe illness with a fever should wait to get vaccinated until their symptoms lessen.

The Centers for Disease Control and Prevention (CDC) recommends that people get immunized as soon as the flu vaccine becomes available in their community. Flu vaccine is produced by private manufacturers, so availability depends on when production is completed. Shipments usually begin in August and continue throughout September and October until all vaccine is distributed. Influenza seasons are unpredictable and can begin as early as October. Usually, seasonal flu activity peaks in January or February.

It takes about two weeks after vaccination for antibodies to develop that will provide protection against the flu. In the meantime, you are still at risk for getting the flu. For this reason, it’s best to get vaccinated early in the fall, before the flu season really gets under way.

Flu vaccines are offered in many locations, including doctors’ offices, clinics, health departments, pharmacies, college health centers, many employers, and some schools.

The viruses in the flu shot are killed, so you cannot get the flu from a flu shot. Minor side effects of the flu shot may occur and may include

• Soreness, redness, or swelling where the shot was given
• Low-grade fever
• Aches

If these problems occur, they begin soon after the shot and usually last one to two days. On rare occasions, flu vaccination can cause serious problems, such as severe allergic reactions.

The viruses in the nasal spray flu vaccine are weakened and do not cause the severe symptoms often associated with flu illness. In children, possible side effects of the nasal spray include

• Runny nose
• Wheezing
• Headache
• Vomiting
• Muscle aches
• Fever

In adults, side effects of the nasal spray include

• Runny nose
• Headache
• Sore throat
• Cough

In both children and adults, side effects of the nasal spray flu vaccine tend to be mild and short-lived.

The protective ability of a flu vaccine depends on the age and health status of the person getting vaccinated, and how well the virus strains in the vaccine match those circulating in the community. The closer the match, the more effective the vaccine will be.

Several months before each flu season, experts predict which strains will be circulating during the upcoming season and begin development of a vaccine against three of those strains. But because flu viruses are constantly changing, it is not possible to predict with certainty which flu viruses will predominate during a given season. Thus, there is always the possibility of a less than optimal match between circulating viruses and viruses in the vaccine.

In recent years, the match between the vaccine viruses and those identified during the flu season has usually been good. In 18 of the 22 U.S. flu seasons between 1990 and 2011, the viruses in the flu vaccine have been well-matched to the predominant circulating viruses.

However, even when the viruses are not closely matched, the vaccine can still protect many people and prevent flu-related complications. Since the seasonal flu vaccine contains three viruses, even when there is lower effectiveness against one virus, the vaccine may protect well against the other two.

Over the course of a flu season, CDC studies samples of circulating flu viruses to evaluate how close a match there is between them and the viruses used to make the vaccine. Data are published in the weekly FluView.

Influenza vaccine production and distribution are primarily private sector endeavors. Manufacturers start producing flu vaccine six to nine months before distribution begins in the late summer or early fall. Since not all of the vaccine supply is ready by this time, distribution to healthcare providers takes place in a phased fashion over several months, usually ending in late November or early December. Manufacturers and distributors aim to get some vaccine to all providers early in the season, because all providers serve at least some high-risk patients and their household contacts.

The U.S. Department of Health and Human Services (HHS) and CDC do not preside over flu vaccine distribution. However, HHS has made significant efforts to improve production capacity of seasonal flu vaccines, including supporting manufacturers as they work to improve their production process and providing guidance about vaccine approval at the Food and Drug Administration.

Take everyday prevention actions to stop the spread of germs:

• Cover your nose and mouth with a tissue when you cough or sneeze. Throw away the tissue after you use it.
• Wash your hands often with soap and water or use an alcohol-based hand rub.
• Avoid touching your eyes, nose, and mouth.
• Try to avoid close contact with sick people.
• Stay home for at least 24 hours after your fever is gone, except to get medical care or for other necessities if you are sick with flu-like ilness.
• Limit your contact with others as much as possible to keep from infecting them while you're sick.

There is no scientific evidence that any herbal, homeopathic, or other folk remedies have any benefit against influenza. In certain situations, antiviral medications may be used to prevent the flu.