Influenza vaccine: How ‘encouraging’ should one be?

September 2002

---Philip A. Brunell, MD

The 2002 ACIP recommendations on influenza (MMWR. 2002;51[RR03]:1-31) contain the following statement concerning the immunization of well children: “Because young, otherwise healthy children are at increased risk for influenza-related hospitalization, influenza vaccination of healthy children aged 6-23 months is encouraged when feasible. Vaccination of children aged >6 months who have certain medical conditions continues to be strongly recommended.” Thus there is a distinction made between the “strong recommendation” for children at high risk which has been recommended previously and the new one for healthy children aged 6-23 months. We now need to decide how encouraging to be and what is feasible.

There are some obvious obstacles to the universal immunization of infants and young children against influenza. These are recognized in the ACIP statement. The Vaccine for Children (VFC) program will not cover the cost of influenza vaccine for 2002 although it is anticipated that it will in the future. Coverage by HMOs and insurance plans are still to be negotiated. In addition, the Vaccine Injury Compensation Program will not cover adverse reactions associated with influenza vaccine given to this group of healthy children at this time. There is no excise tax on this vaccine and there is not likely to be until it is recommended for routine use. Certain groups of children can receive influenza vaccine under the VFC program, including those with chronic pulmonary or cardiac disorder, including asthma; those who are under continuing care for metabolic diseases; those who are receiving long-term aspirin therapy; those who are household contacts of high-risk individuals; those who live in chronic care facilities; or women younger than 19 who are in their second or third trimester of pregnancy. Children younger than 9 years of age who are receiving influenza vaccine for the first time require two doses. This would have to be fitted into an already crowded shot schedule. Finally, for what it is worth, influenza vaccine contains thimerosal.

Influenza virus infections in children can be quite severe and certainly worth preventing. That influenza is more severe in the very young can be gleaned from the mortality rates by age during the great pandemic of 1917-19 in which the risk of death from influenza in this group was exceeded only by those over the age of 80. That the young are at great risk of hospitalization has been confirmed by two recent studies in the Jan. 27, 2000 issue of The New England Journal of Medicine. In both these studies, the authors teased out cases of influenza from those of respiratory syncytial virus (RSV) and other respiratory viruses which overlap during the winter season. The risk of hospitalization in one study was 1:500 in children younger than 2 and in a second was 1:200 to 1:625 for children younger than 1 year of age. However, the morbidity produced by influenza virus also is reflected in outpatient visit 6-15/100 and number of increased prescriptions filled.

Other respiratory infections

Clinically, distinguishing influenza from other respiratory virus infections is very difficult. The classical picture of flu which we see in adults and older children and adolescents is uncommon in the very young. All of the respiratory viruses cause bronchiolitis, pneumonia, upper respiratory infection, croup and other symptoms and are indistinguishable one from the other without laboratory confirmation. Herein lies another problem.

When we discuss what one can expect as a result of giving influenza vaccine to a child it must be made clear that this vaccine can prevent one of five to 10 respiratory viral infections that young children may be expected to get annually. It is not a cold vaccine! The severity of influenza virus infection, however, is probably second only to RSV. In two studies in this age group (JAMA. 2000;284:1677 and J Infect Dis. 2000;182:1218) immunization with influenza vaccine did not result in a reduction in respiratory illness. It may, however, have prevented influenza, one of the many agents producing respiratory illness. Killed vaccines, however, have not been shown to be very effective in this age group. In one recent study the efficacy was found to be 45% for influenza B and 31 % for influenza A. It may prevent some cases of otitis media associated with influenza virus but it is not likely to have a noticeable impact on ear infections.

Influenza infections are severe and are worth preventing. The downside of giving influenza vaccine, however, is raising expectations. It would be unfortunate at this time to have parents come away with the impression that influenza vaccines do not work as we soon may have a live-attenuated intranasal vaccine that may be more effective, will not require injections and may yield longer and broader protection than the killed vaccine we now use.

Adequate supply

It is anticipated that there will be adequate vaccine for this year’s influenza campaign. However, all of the vaccine will probably not be delivered on Oct. 1, the optimal time to start immunization. Children who will require two doses should receive their first dose early. The second dose can be given a month later. People at increased risk and health care workers should also be immunized early. Vaccination for other groups should begin in November and continue. Although early immunization is optimal, those showing up in December or even in early 2003 should be given vaccine.

I take influenza vaccine myself every year. Two of the three most severe illnesses I have experienced in my lifetime have been caused by influenza virus. What is more, you owe it to your patients not to pass on influenza infection to them that you have acquired. This is particularly true for those younger than 6 months of age who cannot be immunized. I would be particularly punctilious about getting neonatologists immunized. Children at increased risk of morbidity from influenza should be immunized and those who may expose others at high risk, e.g. grandma and grandpa. Those with asthma should be immunized being cognizant that the vaccine is prepared in eggs and those allergic to eggs probably should not be offered it. Be certain that women in the last two trimesters of pregnancy are offered vaccine. As for healthy kids between 6-36 months of age, “encourage” and give “where feasible.” Be prepared for some long conversations but do not withhold vaccine from normal kids whose parents want their children to be immunized.