Due to slight changes, called mutations, in the genetic material of the influenza viruses A and B, new virus strains emerge each year. At present, strains of influenza (2 influenza A strains and 1 influenza B strain) co-circulate in humans. To be protected from getting influenza, you need to be vaccinated against all three each year.
Twice a year, the World Health Organization (WHO) makes a recommendation about which influenza strains should be included in the vaccine for the next winter season (Northern and Southern Hemispheres). The new vaccines are manufactured in accordance with these recommendations. The new vaccine becomes available for use in the months before the start of the next winter season.
The small, almost yearly, genetic changes should not be confused with a major genetic “shift”. Such a shift might lead to the creation of a completely new, and potentially lethal human influenza virus to which humans have not been exposed before and for which they have little or no resistance.
These major events – where genetic material from a bird influenza virus is incorporated into the genetic material of an existing human influenza virus – tend to occur every twenty to thirty odd years, and the next one, according to epidemiologists, is long overdue.
How do vaccines work?
Influenza vaccines are produced from killed viruses. Since it does not contain the live virus, the vaccine cannot cause 'flu and can be administered safely to people with weakened immune systems.
Within one to two weeks after receiving the vaccine, the body produces antibodies which will fight the virus if the vaccinated person is exposed to influenza. These antibodies either prevent infection or reduce the severity of symptoms. Although the antibodies will prevent infection with the three viral strains present in the vaccine, there is no guarantee that you won’t get sick during winter. This is because there are many other viruses (not covered by the vaccine) that can cause influenza-like illnesses.
Influenza vaccine is usually given in one dose as an injection into the muscle (usually the upper arm). Children under the age of three should receive half the adult dose. If children under nine years of age have not been vaccinated before, they should receive a second vaccination one month later.
Studies have shown that:
- The 'flu vaccine prevents 'flu in 70 to 90 percent of young adults, but, unfortunately, in only 30 - 40 percent of the elderly. However, it does reduce the severity of the infection, thereby decreasing hospitalisation by about 70 percent, and reducing the risk of death by about 80 to 85 percent.
- Among nursing home residents, vaccination can reduce the risk of hospitalisation by about 50 percent, the risk of pneumonia by about 60 percent, and the risk of death by 75 - 80 percent.
- 'Flu vaccination can reduce absenteeism from the workplace by 50 percent.
Despite the benefits thereof, the majority of people choose not to be vaccinated against the 'flu. The reasons are not quite clear. Fear of needles, as well as a lack of knowledge about its availability and effectiveness, may be factors that lead to low enthusiasm for the annual 'flu vaccine.
Who should be vaccinated?
Any person who wishes to reduce the likelihood of becoming ill with 'flu, should be vaccinated.
Specifically, the 'flu vaccine is strongly recommended for any person over the age of six months who is at an increased risk to develop 'flu complications.
Adults in the high-risk group include:
- All people aged 65 and older, especially those living in retirement homes;
- Anyone with a heart problem, such as heart failure;
- Anyone with a respiratory problem, such as asthma or emphysema;
- Anyone with other chronic illnesses such as anaemia, diabetes or kidney failure;
- The immune suppressed, including persons with HIV-infection, or people receiving long-term corticosteroid treatment, or cancer patients receiving radiation or chemotherapy. In the case of HIV, people with a CD4 count of less than 200 per microlitre are unfortunately unlikely to respond to the vaccine;
- People who have required regular visits to the doctor or have been hospitalised during the preceding year due to chronic illnesses;
- Women in their second and third trimester of pregnancy (pregnancy can increase the risk for serious medical complications from influenza);
- Pregnant women in their first trimester if they have a medical condition that increases their risk for complications;
- Caregivers of the ill, staff at nursing homes and other facilities that provide care for chronically ill persons, health-care workers, and home-care providers – to protect themselves from infection and to reduce the risk of transmitting 'flu to their high-risk patients or clients;
- Persons in close contact with any high-risk individual;
- People planning to travel to the tropics at any time or to the northern hemisphere between October and February;
- Police, ambulance personnel, fire fighters, and other community service providers.
The Centres for Disease Control and Prevention (CDC) in Atlanta, USA, recommends that people at risk of 'flu complications should be vaccinated against pneumococcal infection as well, as this complication can be fatal. This vaccination may be given at the same time as the 'flu vaccination.
Children and teens in the high-risk group include:
- All children between the ages of 6 and 23 months, as their immunity levels against diseases are at its lowest and their exposure rate high if they attend a crèche;
- All children who have chronic heart or lung disorders, including asthma;
- All children who have chronic illnesses, as well as those who have required hospitalisation or regular visits to the doctor during the preceding year;
- All children who live with someone in a high-risk group;
- All children and teenagers (from six months to 18 years of age) on long-term aspirin therapy, because of the dangers of Reye's syndrome if they catch the 'flu and run a fever;
- School-aged children are two to three times more likely than adults to get influenza, and to rapidly spread the virus to others. Studies have shown that families with school-aged children have more infections than other families.
Take note that haemophilus influenza type b is not the cause of 'flu, but a bacterium that causes meningitis, ear infections, pneumonia and other infections. Talk to your doctor about this vaccination.
The 'flu vaccine is also recommended for persons between ages 50 to 65 because they are often in close contact with high-risk family members (see above), and because 50 is an age when other chronic illnesses may become more common.
Breastfeeding moms may also receive the 'flu vaccination without affecting the safety of the infant.
Who should not be vaccinated?
Some people shouldn't be vaccinated. Examples are:
- People allergic to eggs (the protein albumin) should be careful, because the vaccine virus is grown in eggs. However, if deemed necessary, even such persons may be able to be vaccinated under close medical supervision;
- People with a history of side effects with previous vaccinations. Under certain conditions, the vaccine might be given in two half doses;
- It is advisable to delay being vaccinated if the person is ill with a high fever or any acute illness;
- Although in the case of the influenza vaccine there are no known adverse effects to the foetus (associated with the mom being vaccinated), vaccines are generally avoided in the first trimester of pregnancy;
- Individuals who developed Guillain-Barré syndrome within six weeks after receiving a previous vaccination, should not be vaccinated. This risk was associated with older forms of the vaccine, and not with newer forms of the vaccine, but the recommendation stands.
Consult your doctor/health care professionals if you think you should not be vaccinated or if you are uncertain.
Side effects might occur in some people
Side effects usually consist of low-grade fever and mild 'flu-like symptoms, lasting eight to 24 hours after immunisation. These symptoms occur due to the response of your immune system to the vaccine.
- Mild redness and soreness at the site of the injection is common - this will only last a day or two;
- About 5 - 10 percent of people may experience fever, malaise, sore muscles, and other symptoms resembling 'flu that can start within twelve hours of receiving the 'flu shot. It will last only 24 hours. These symptoms are not uncommon in children and the elderly.
If you experience these symptoms for more than a day after you have been vaccinated, or if they last longer than two days, it is almost certainly an illness not related to the vaccine. Please consult your doctor or health care professional.
When is the best time to be vaccinated?
It takes the immune system about two weeks to produce specific antibodies against the 'flu strains in the vaccine, and six to eight weeks for the development of a maximal immune response to vaccination. This means that the best time to be vaccinated against the 'flu is during the months of February through to April (for the southern hemisphere), before the 'flu season typically starts.
However, there is no cut-off date for 'flu vaccination - it can be given at any stage during the winter.
Reviewed (2006) by Dr Jane Yeats MBChB, BSc(Med)(Hons)Biochem, FCPathSA(Virology).