This coming flu season will be interesting—and confusing. As of August 6, 2009, the Centers for Disease Control and Prevention (CDC) reported 6506 hospitalized cases and 436 deaths from the pandemic H1N1 flu virus since the first US cases were reported in April 2009.1 (Reporting on individual confirmed and probable cases has been discontinued.) On July 31, the World Health Organization reported pandemic influenza in 168 countries, with 162,380 reported cases and 1154 deaths.2 At the same time the pandemic was developing, the seasonal flu of 2009—a relatively mild year—was tapering off. The pandemic influenza has continued to cause widespread disease in the United States throughout the summer, a somewhat unusual pattern for influenza.
So far, pandemic H1N1 flu is relatively benign, treatable
The pandemic virus, though highly infectious, has had a low case fatality rate up to now. Deaths have occurred predominantly in those with underlying medical conditions that put them at high risk of infection. Attack rates for those older than age 65 have been lower than expected, indicating that this age group may have some immunity based on past infection. The pandemic virus so far has been sensitive to both oseltamivir (Tamiflu) and zanamivir (Relenza). The resistance patterns of the key viruses from last flu season showed that the H1N1 seasonal virus was resistant to oseltamivir but sensitive to zanamivir and the adamantanes (rimantadine and amantadine), while the H3N2 virus that circulated last year was sensitive to oseltamivir.3
Fall flu season: Be prepared
So, what can you expect this fall? With pandemic H1N1 still causing illness and strains of seasonal virus circulating elsewhere in the world, no one knows for sure. But it is very likely that we will experience much higher rates of pandemic influenza once schools reopen and children begin to congregate. It is also likely we will have pandemic influenza circulating along with seasonal influenza viruses this fall and into 2010.
Immunize for seasonal flu, now
The 2009-2010 seasonal influenza vaccine will contain antigens from 3 strains: a nonpandemic H1N1 influenza A strain, an H3N2 influenza A strain, and an influenza B strain.4 These 3 antigens will be in all seasonal influenza vaccine products, whether they are the trivalent influenza vaccine given by injection or the live attenuated influenza vaccine provided as a nasal spray. The CDC is recommending immunization against seasonal influenza as soon as the vaccine is available.
The groups for whom seasonal influenza vaccine is recommended have not changed from last year. The recommendations are summarized in the TABLE.
TABLE
Who should get seasonal flu vaccine, 2009-2010?
| All children and adolescents ages 6 months through 18 years |
| Adults ≥50 years of age |
| Individuals at risk for medical complications |
| Women who will be pregnant during the influenza season |
| Adults and children who have chronic pulmonary (including asthma), cardiovascular (except hypertension), renal, hepatic, hematologic, or metabolic disorders (including diabetes mellitus) |
| Adults and children who have immunosuppression (including immunosuppression caused by medications or by HIV) |
| Adults and children who have any condition (eg, cognitive dysfunction, spinal cord injury, seizure disorder, or other neuromuscular disorder) that can compromise respiratory function or the handling of respiratory secretions or increase the risk for aspiration |
| Residents of nursing homes and other chronic-care facilities |
| Individuals who live with, or care for, people at high risk for influenza-related complications |
| Health care personnel |
| Healthy household contacts (including children) and caregivers of children <5 years of age and adults ≥50 years |
| Healthy household contacts (including children) of individuals with medical conditions that put them at higher risk for severe complications from influenza. |
| Source: Centers for Disease Control and Prevention. MMWR Recomm Rep. 2009.4 |
Pandemic flu vaccine will be available in the fall
The vaccine for pandemic H1N1 is being produced, and the Department of Health and Human Services is projecting it to be available starting in mid- to late October. The supply will be limited at first, with increasing quantities produced as time progresses. The intent is to produce 600 million doses, or 2 per US resident, since 2 doses will be required.
Who should get the vaccine for pandemic H1N1? At its meeting at the end of July, the Advisory Committee on Immunization Practices (ACIP) recommended that vaccination efforts focus on 5 key populations:
- pregnant women
- people who live with, or care for, children <6 months of age
- health care and emergency services personnel
- individuals between the ages of 6 months and 24 years
- individuals 25 to 64 years of age who are at higher risk for novel H1N1 because of chronic health disorders or compromised immune systems.