Vidyya Medical News Service
Volume 6 Issue 3 Published - 14:00 UTC 08:00 EST 3-Jan-2004 Next Update - 14:00 UTC 08:00 EST 4-Jan-2004
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Information for clinicians: General questions and answers about the 2003-2004 influenza season

General Questions and Answers

Why was the A/Fujian strain not included in this season's vaccine for the Northern Hemisphere?
Production of influenza vaccines is a complex process that requires many steps, including selection of suitable vaccine viruses, growth of these viruses in eggs, and testing to ensure safety and purity of the vaccine. Recommendations about which strains should go into the vaccines for the United States are based on year-round surveillance and are typically made in February for vaccine that will be used in the following season.

The A/Fujian strain was identified late in January 2003. At that time, it seemed possible that this strain might predominate during the coming flu season, but it was too early to be certain. In addition, there was no isolate that had been grown exclusively in eggs. All influenza viruses used in vaccine production must be grown only in eggs or avian cell culture, while most viruses obtained through surveillance are grown in mammalian cell culture.

U.S. health authorities postponed their recommendation about which A (H3N2) strain should be included in the vaccine for a full month (until March) while more viruses were tested and while attempts were made to grow an egg isolate of the A/Fujian virus that could be used in vaccine production. A suitable isolate could not be grown in time and waiting longer likely would have jeopardized the supply of influenza vaccine for the 2003-04 season. Because of these considerations, in March it was recommended that the influenza vaccine for the 2003-04 influenza season include an A/Panama strain, which is related to the A/Fujian strain.

Questions and Answers for Health Care Professionals

Dec 19, 2003
Why are two doses of influenza vaccine necessary for children under 9 years of age who have never been previously vaccinated?
In young children who have never been infected with influenza virus, the first influenza vaccination “primes” the immune system and helps it to better recognize and respond to influenza viruses. When a second vaccination is given (at least 1 month after the first dose), the immune system then responds by producing antibodies that provide protection against influenza. Since one dose of vaccine may not lead to optimal levels of antibodies, a second vaccination is recommended for children younger than 9 years old. Two influenza vaccinations are particularly important for young children who have never been exposed to influenza before.

Is one dose of influenza vaccine sufficient for previously unvaccinated children 6 months through 8 years of age? What level of protection does one dose provide?
It is possible that one dose of vaccine in a child younger than 9 years of age could provide protection against influenza. Studies in the 1970s suggested that between 10% and 40% of children 6 months through 12 years of age produced substantial antibody levels with one dose of influenza type A/h3N1 vaccine, and as many as 67% to 85% of children 6 months through 12 years of age produced substantial antibody levels to influenza type B and influenza type A/H3N2 viruses with one dose of vaccine. However, the degree of protection remains unknown because there are no vaccine efficacy studies showing how much protection is provided by one dose versus two doses of influenza vaccine in young, previously unvaccinated children.

Given the recent shortage of injectable trivalent inactivated influenza vaccine, should we give one influenza vaccine dose to as many children as we can or two doses to young children at high risk for complications from influenza at the expense of low-risk older children?
CDC recommends that all high-risk children, including those 6-23 months of age, who present for vaccination be vaccinated with a first or second dose, depending on vaccination status. Doses should not be held in reserve to ensure that two doses will be available. Although the vaccine effectiveness of one dose is uncertain, it may provide protection. It is also possible that the influenza activity will decrease before a second dose is indicated or that some children might not return for a second dose.

Given the recent shortage of injectable trivalent inactivated influenza vaccine, how do we pri oritize vaccination for adults and older children?
Emphasis should be placed on targeting injectable trivalent inactivated influenza vaccine to persons at highest risk for complications from influenza, including all children aged 6-23 months, adults aged 65 years and older, pregnant women who are in their second and third trimester during influenza season, and persons aged 2 years and older with underlying chronic medical conditions. Second priority should be given to vaccinating those individuals at greatest risk for transmission of disease to high-risk individuals, including household contacts and health care workers.

Are there any other options for vaccination of healthy people who wish to reduce their chance of developing influenza disease?
An intranasally administered live, attenuated influenza vaccine (LAIV) is available for the first time this year and is approved for healthy people 5 to 49 years of age.

Can we administer Fluvirin influenza vaccine (manufactured by Evans Vaccines) to children younger than 4 years of age?
No. Fluvirin is not licensed for children younger than 4 years of age because data demonstrating efficacy of this vaccine in that age group have not been provided to FDA.

Can we give 2 doses of the 0.25mL pediatric formulation of Fluzone (manufactured by Aventis Pasteur) to persons 3 years of age and older who require a 0.5mL dose?
Two 0.25mL doses of Fluzone administered at the same time can be considered equivalent to a single valid 0.5mL dose. Vaccine should not be transferred from one syringe into another syringe to administer two 0.25mL doses with a single injection.

Can we split a 0.5mL injectable trivalent inactivated influenza vaccine dose from a single-dose syringe to give a 0.25mL dose to a child under 3 years of age?
No. This practice could lead to unequal doses of vaccine or vaccine wastage, and it could lead to contamination of the vaccine. However, withdrawing (0.25mL) adult formulation injectable trivalent inactivated influenza vaccine for pediatric use (children up to 35 months of age) from a 10-dose vial is acceptable.

The Evans pre-filled syringe (Fluvirin) comes with a 5/8-inch needle, but a 1-inch needle is recommended for intramuscular injections. Can the vaccine be administered using a 5/8-inch needle?
Yes, the FDA has licensed this needle as part of the Evans package and the Evans pre-filled syringe may be used to administer influenza vaccine to persons 4 years of age and older.

If I'm at high risk for complications from influenza but have already had influenza, should I still be vaccinated?
Yes. There are 3 main influenza viruses, and infection with one virus does not protect against the other 2. Therefore it is possible to become infected with a different influenza virus later in the season. The influenza vaccine contains three different viruses and provides protection against all 3 viruses.

I heard that this season's influenza vaccine is ineffective for the strain of influenza that is going around. Is that true?
The influenza type A (H3N2) strain in this season's influenza vaccine is related but somewhat different from the predominantly circulating strain causing illness in the United States . Laboratory studies suggest that the vaccine should still provide some protection against the circulating influenza A (H3N2) strain. However, clinical vaccine effectiveness studies are needed to provide a more definitive answer. The other two strains in the vaccine are well matched to their circulating counterparts.

What if I can't get the vaccine?
The single best way to prevent influenza is to get vaccinated each fall. In the absence of vaccine, however, there are other ways to protect against influenza. Four antiviral drugs (amantadine, rimantadine, oseltamivir and zanamivir) are approved and commercially available for use in treating influenza. Three of them (amantadine, rimantadine and oseltamivir) are approved for prevention (chemoprophylaxis) against influenza. All of these drugs are prescription drugs, and a doctor should be consulted before their use.

In addition, the following simple steps may help prevent the spread of respiratory illnesses like influenza:

  • Avoid close contact with people who are sick and keep your distance from others when you are sick.
  • Wash your hands often to keep from picking up germs.
  • Cover your mouth and nose with a tissue when coughing or sneezing. It may prevent those around you from getting sick.
  • Stay home when you are sick.

Does CDC have any recommendations for use of the pneumococcal vaccine for preventing complications in influenza cases?
Adult target groups for influenza and pneumococcal polysaccharide vaccination overlap considerably. For persons at high risk who have not previously been vaccinated with pneumococcal vaccine, health-care providers should strongly consider administering pneumococcal polysaccharide and inactivated influenza vaccines concurrently. Both vaccines can be administered at the same time at different sites without increasing side effects. Pneumococcal polysaccharide vaccine (PPV) should be routinely administered to all adults 65 years of age and older. PPV also is indicated for persons aged 2 years and older with normal immune systems who have chronic illnesses, including cardiovascular disease, pulmonary disease, diabetes, alcoholism, cirrhosis, or cerebrospinal fluid leaks. Immunocompromised persons aged 2 years and older who are at increased risk for pneumococcal disease or its complications also should be vaccinated with PPV.

Pneumococcal conjugate vaccine (PCV) should be routinely administered to all children younger than 24 months of age and children aged 24-59 months with medical conditions that increase their risk of serious pneumococcal disease, such as sickle cell disease, absence of a spleen, immunosuppression, and other chronic medical conditions.

Moderate or severe illness at the time of vaccination is a precaution whether due to influenza or to some other cause.

Vidyya thanks for Centers for Disease Control for the valuable information it makes available in the public domain

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