Influenza epidemics: Be prepared for any influenza eventuality this season

September 2006

As avian flu occurrences have reached more than 200 human cases, we prepare for it and for the latest conventional flu epidemic. It is important for those caring for children to start their preparation now. Children younger than 9 years who have not previously had an influenza vaccine need to receive two doses at least four weeks apart (six for intranasal vaccine); this means starting in October in order to provide protection prior to the onset of flu season.

It has been several decades since we have had a major flu epidemic, but each year these viruses exact their toll. Our annual “flu season” will result in millions of infections, substantial time lost from work or school and thousands of deaths. So, we prepare. This year, we will immunize children in an expanded age group, be certain that those who have not had the vaccine previously receive two doses in the same season, and use the neuraminidase inhibitors rather than the M2 channel inhibitors to treat. We also will ensure that those who are most vulnerable or those who might expose such individuals are immunized. The vaccine for the coming season will contain: A/New Caledonia/20/1999 (H1N1)-like strains; A/Wisconsin/67/2005 (H3N2)-like strains; and B/Malaysia/2506/2004-like strains. A tiered priority system has been developed if there is a problem with supply. Pediatric patients will be among those in the higher priority groups.

Children and flu

It has been clear since as early as the 1917 to 1919 epidemic that young children are among the most severely affected by influenza. It is recognized that children are excellent disseminators of respiratory infections for a variety of reasons: some not so apparent, such as the higher titer of virus shedding for longer periods; and some quite obvious, like the ease with which young children share their respiratory secretions. With development of better diagnostic methods, several decades ago it became apparent that young children may exhibit responses to respiratory viral infections, including influenza, in a variety of ways: bronchiolitis, croup, otitis, pneumonia, febrile seizures, apnea in neonates, as well as the cough, coryza, and fever syndrome so familiar in adults. Thus, it is reasonable to expand immunization practices to include infants and children, in order to decrease morbidity in this age group and to reduce spread to contacts.

Routine immunization is now recommended for children aged 6 to 59 months and their contacts, as well as those likely to experience severe influenza or those who may come in contact with the latter (eg, parents, child or health care workers or children exposing grandparents). Particular attention should be given to those likely to expose infants aged younger than 6 months. Two doses, one month apart for killed vaccine, and at least six to 10 weeks apart for live vaccine are recommended for those younger than 9 years who have not been immunized previously. Live vaccine is approved only for those children older than 60 months, though an application has been filed with FDA recently for children as young as 12 months. Those who have received a single dose of vaccine in the previous season need only receive one rather than two doses of vaccine in the current season. Counting a vaccine given the previous spring as the first dose for the coming flu season is not recommended. Breast-feeding is not a contraindication to immunization of mothers; however, if the live-attenuated influenza vaccine (FluMist, MedImmune) is administered to nursing mothers, it should be done with caution.

Since 2001, thimerosal has been absent or present in only trace amounts in influenza vaccine for infants in the United States. There is none in the live influenza vaccine. All influenza vaccines at the present time are produced in eggs. People who have had hives or swollen lips or tongue, or who have had acute respiratory distress or collapse after eating eggs should consult a physician to determine if vaccine should be administered. Asthma was more common two weeks post immunization with the first dose of live vaccine. The package insert should be consulted for restrictions in the use of live influenza vaccine including immunocompromised vaccinators.

About the flu vaccines

Fluzone vaccine (Sanofi-Pasteur) is approved for infants older than 6 months. The inactivated influenza vaccine Fluvirin (formerly Chiron, now Novartis) is labeled in the United States for use among people older than 4 years. Fluvarix (GlaxoSmithKline) is labeled for use in people older than 18 years. The LAIV is approved for use by healthy people aged 5 to 49 years.

Oseltamivir (Tamiflu, Roche) or zanamivir (Relenza, GlaxoSmithKline) can be prescribed if antiviral treatment of influenza is indicated. Oseltamivir is approved for treatment of people older than 1 year, and zanamivir is approved for treatment of people older than 7 years. Oseltamivir and zanamivir can also be used for chemoprophylaxis of influenza; oseltamivir is licensed for use in people older than 1 year, and zanamivir is licensed for use in people older than 5 years. Amantadine (Flumadine, Forest) and rimantadine are no longer recommended in the United States because of high levels of resistance. Resistance to neuraminidase inhibitors in children has been reported, but is uncommon. To be effective, treatment must be initiated soon after onset of symptoms. One can expect a one-day shortening of symptoms if started within two days after onset. Otitis has been less common in treated patients. A twice-daily dosage, which will vary by weight, is recommended. Vomiting is associated with the use of oseltamivir in children.

As children often are the first in the community to get influenza during epidemics and since they may not have classic adult symptoms, rapid diagnostic tests, some of which are CLIA waived, are available. They generally are less sensitive than PCR or virus isolation. Nasopharyngeal specimens are typically more effective than throat swab specimens.

As we prepare for an influenza epidemic we can only wonder if this will be the big one. One can take the pessimistic view and believe that avian flu will eventually be transmitted among humans or the optimistic one and say that it is been around long enough to have happened if it was going to. In any case, it is well to be prepared for any flu eventuality. Two of the three most memorable illnesses I have had were influenza and thus, I have great respect for this virus.

For more information:

• VFC. www.cdc.gov/nip/vfc/default.htm.
• CDC. Prevention and control of influenza. MMWR. 2006;55(RR10);1-42.