When should we immunize?
Immunization of those at high risk should begin in September (if vaccine is available) or October. This is particularly important for children who need 2 doses for protection. Vaccination in nursing homes is best started in October—early enough to provide protection throughout the season but late enough to provide more assurance immunity will last throughout a late season. Vaccination of all those at risk should continue throughout the whole season, or as long as vaccine supplies last.
Will there be an adequate supply of vaccine?
There will be between 100 million and 120 million doses of vaccine available this year. Based on prior years, this should be an adequate supply.
Information is available on the American Academy of Family Physicians (AAFP) Web site on current vaccine supply issues and how to purchase influenza vaccine (available at: www.aafp.org/online/en/home/clinical/immunizations/flu06/ordering.html). The AAFP Web site will also contain information on vaccine prioritization should a shortage develop.
What is the role of antiviral medications?
The CDC currently recommends that the adamantanes (amantadine [Symmetrel] and rimantadine [Flumadine]) not be used for treatment or prophylaxis of influenza A because of a high rate of resistance documented last flu season. This situation could change as the current influenza season progresses. The remaining antivirals are both neuraminidase inhibitors; oseltamivir (Tamiflu—licensed for use in treatment and prophylaxis beginning at age 1 year) and zanamivir (Relenza—licensed for treatment beginning at age 5 years and prophylaxis at age 7 years).
Chemoprophylaxis is most useful in those whom the vaccine is contraindicated; in the 2 weeks after receipt of a vaccine, which is the time needed for it to be effective (2 weeks after the second dose in children receiving the vaccine for the first time); when the circulating virus does not match the vaccine; in those who are immune-suppressed and may have an inadequate response to the vaccine; and in nursing homes where there is an outbreak, when it should be used for everyone regardless of their vaccine status.
Treatment of those with influenza A can shorten the illness and reduce its severity if started within 2 days of symptoms. Details on antiviral recommendations and doses for treatment and prophylaxis can be found in the annual CDC influenza recommendations.3
Are rapid office lab tests useful?
The gold standard for laboratory confirmation of influenza is viral culture from a nasopharyngeal swab or washing. The time needed for this creates some difficulty initiating antiviral therapy within the two day window. Rapid, office-based tests are available and are listed in TABLE 3.5 Some of these tests are specific for influenza A, others for influenza B, and some are for both. The sensitivities and specificities for each product vary. A negative test in a highly suspicious patient should not rule out the disease, especially in a high prevalence situation. In a low prevalence situation a positive test is more likely to be a false positive than when the virus is causing an outbreak in the community.
TABLE 3
Rapid (<30-minute) laboratory tests available for influenza
| RAPID DIAGNOSTIC TESTS | INFLUENZA TYPE | APPLICATION METHODS |
|---|---|---|
| Directigen Flu A* (Becton-Dickinson) | A | NP swab, throat swab, nasal wash, nasal aspirate |
| Directigen Flu A+B* (Becton-Dickinson) | A and B† | NP swab, throat swab, nasal wash, nasal aspirate |
| Directigen EZ Flu A+B* (Becton-Dickinson) | A and B† | Throat swab, nasal wash, nasal aspirate |
| FLU OIA* (Thermo Electron) | A and B‡ | NP swab, throat swab, nasal aspirate, sputum |
| FLU OIA A/B* (Thermo Electron) | A and B† | NP swab, throat swab, nasal aspirate, sputum |
| XPECT Flu A&B* (Remel) | A and B† | Nasal wash, NP swab, throat swab |
| NOW Influenza A & B* (Binax) | A and B† | Nasal wash, NP swab |
| QuickVue Influenza Test** (Quidel) | A and B‡ | NP swab, nasal wash, nasal aspirate |
| QuickVue Influenza A+B Test** (Quidel) | A and B‡ | NP swab, nasal wash, nasal aspirate |
| SAS Influenza A Test* | A† | NP wash, NP aspirate |
| SAS Influenza B Test* | A† | NP wash, NP aspirate |
| ZstatFlu† (ZymeTx) | A and B‡ | Throat swab |
| Table may not include all test kits approved by the US Food and Drug Administration. | ||
| NP, nasopharyngeal | ||
| * Moderately complex test—requires specific laboratory certification. | ||
| † Distinguishes between influenza A and B virus infections. | ||
| ‡ Does not distinguish between influenza A and B virus infections. | ||
| ** CLIA-waived test. Can be used in any office setting. Requires a certificate of waiver or higher laboratory certification | ||
| Source: Centers for Disease Control and Prevention.5 | ||
CORRESPONDENCE
Doug Campos-Outcalt, MD, MPA, 4001 North Third Street #415, Phoenix, AZ 85012. E-mail: dougco@u.arizona.edu