TREATMENT AND CHEMOPROPHYLAXIS IN SPECIAL PATIENT POPULATIONS
Pregnant patients. Pregnant women infected with the H1N1virus usually present with an ILI and may have a self-limited bout of uncomplicated influenza illness. However, maternal illness maybe more severe, with rapid progression of symptoms or secondary bacterial complications and fetal distress. It is therefore prudent to test pregnant patients with ILI for H1N1 by obtaining specimens for a real-time polymerase chain reaction test, as outlined in "Diagnostic Testing for H1N1 Flu: When and How."
If a pregnant woman meets criteria for a confirmed, probable, or suspected case of H1N1 influenza, she should receive empiric oseltamivir(Drug information on oseltamivir) as soon as possible, preferably within 48 hours of symptom onset—or even after this window, if she is hospitalized.
Both NAI agents—oseltamivir and zanamivir(Drug information on zanamivir)—are designated "Pregnancy Category C" medications (ie, no clinical studies have been conducted to assess their safety in pregnant women). However, if the benefit outweighs any perceived risk of teratogenicity, therapy for H1N1 infection should be given. Oseltamivir and zanamivir treatment and chemoprophylaxis regimens recommended for pregnant women are the same as those recommended for adults who have seasonal influenza. Recommended duration of treatment is 5 days, and recommended duration of chemoprophylaxis is 10 days.
If a pregnant woman experiences any degree of hyperthermia, the risk of neural tube defects and adverse outcomes almost doubles. As in normothermic pregnant women, multivitamins that contain folic acid(Drug information on folic acid) would likely lessen such risks; it is also reasonable to suggest non-aspirin–containing antipyretics (ie, acetaminophen), which obviate the possibility of Reye syndrome and other complications. Fever during the intrapartum period is also associated with negative outcomes for the infant and thus should be treated expeditiously.
A number of nonpharmacological interventions, including the use of strict infection control practices, can be very helpful in preventing H1N1 infection in pregnant women. More information about the care of pregnant women who have H1N1 infection or who may be exposed to the virus can be found in the CDC guideline, "Pregnant Women and Novel Influenza A (H1N1) Virus: Considerations for Clinicians." This is available at http://www.cdc.gov/h1n1flu/clinician_pregnant.htm.
Infants. Oseltamivir has not been approved for use in children younger than 1 year. However, because infants with influenza experience high rates of morbidity and mortality, an Emergency Use Authorization has been issued by the FDA permitting the use of oseltamivir in infants with novel H1N1 influenza virus infection.9Dosages for antiviral treatment in this age-group are 12 mg bid in infants younger than 3 months, 20 mg bid in those aged 3 to 5 months, and 25 mg bid in those aged 6 to 11 months. For chemoprophylaxis in the last two of these age-groups, simply administer once a day (instead of twice daily); chemoprevention is not recommended at all for infants younger than 3 months unless special considerations warrant it. Dosing recommendations from the CDC for treatment and chemoprophylaxis in infants are summarized in Tables 3 and 4.10 Specific antiviral dosing regimens for infants are available at the CDC Web site.10
When considering oseltamivir use in a seriously ill infant with confirmed or suspected H1N1 influenza, keep in mind the lack of data on safety and dosing for patients this age. Monitor all treated infants carefully for adverse events.
H1N1 VACCINE UPDATE
Fortunately, public health officials were able to identify and isolate the H1N1 virus in the earliest phase of this pandemic so that a seed stock of the virus would be available for vaccine development. The US Department of Health and Human Services has allocated almost $1 billion for H1N1 vaccine clinical trials and candidate vaccine mass production in 2009. Currently, 5 US manufacturers are working to ensure that vaccine supplies are sufficient.
The FDA and the WHO have identified A/California/07/2009 (H1N1) as the vaccine strain, with plans to have available for distribution both live, attenuated and inactivated influenza A(H1N1) 2009 monovalent vaccine formulations. Thus far, as in the case of seasonal influenza vaccine, neither formulation will contain adjuvants.11
Although details are pending, plans are under way to have supplies distributed initially around mid-October. Should the amount of vaccine available in the required time frame be insufficient, the major consequence would be suboptimal protection of certain groups against H1N1 infection.12
Seasonal influenza vaccine will most likely be administered with one of two H1N1 doses. Detailed guidance on the exact number of doses, timing, and the simultaneous administration of the seasonal influenza vaccine is forthcoming. Clinicians are referred to the CDC Web site for upcoming Morbidity and Mortality Weekly Reports monographs (http://www.cdc.gov/mmwr) or other new guidance (http://www.cdc.gov/flu).
Experts anticipate seasonal influenza strains to emerge—including A-H1N1, A-H3N2 and influenza B—for all of which seasonal influenza vaccine (2009-2010) should be an effective preventive measure. Detailed guidance has already been published on seasonal influenza vaccine for the upcoming 2009-2010 season.13 Vaccines will be administered by health departments, clinics, offices, and other entities.
Currently, the following 5 groups are being prioritized at the highest level to receive the vaccine:
•Pregnant women.
•Household contacts and caregivers of children younger than 6 months.
•Health care workers and first responders.
•Persons aged 6 months to 24 years.
•Persons aged 25 to 64 years who are at increased risk for influenza-related complications.14
Depending on vaccine supplies, the US government and the public health community are committed to eventually making the H1N1 vaccine even more widely available.
With regard to the safety of the H1N1 vaccine—a cautionary and realistic note: although predistribution efforts will be made to ensure the safety of the vaccine—including oversight, meticulous safety reviews, and good clinical practice in ongoing and planned clinical H1N1 vaccine trials—it may take field experience involving larger populations to identify some potential vaccine-related adverse events. Informed clinicians and citizens will need to make individual decisions based on the best evidence and guidance available. Based on the 1976 swine influenza vaccine deployment efforts and the incidence of Guillain-Barré syndrome among those vaccinated, it would require that between half a million and a million persons receive the H1N1 vaccine to detect a risk similar to that associated with the 1976 vaccine.
Seasonal influenza vaccine has not thus far provided cross-protection against H1N1 influenza and is unlikely to do so. Finally, the Advisory Committee on Immunization Practices strongly recommends pneumococcal vaccine for persons older than 65 years and those between ages 2 and 64 years who have high-risk conditions.15
