ATLANTA — Initial vaccination efforts against the novel influenza A (H1N1) should focus on immunizing as many people as possible in five target groups, while smaller subsets of some of those groups should be targeted if demand for vaccine exceeds supply. As more supply becomes available, the rest of the population should be targeted for vaccination.
Those recommendations were made by the Advisory Committee on Immunization Practices of the Centers for Disease Control and Prevention at a special 1-day meeting on July 29. Primary targets for novel influenza A (H1N1) immunization efforts include the following five groups, which together total approximately 159 million individuals in the United States. Current seasonal influenza coverage among these groups is only 20%-50%, said Dr. Anthony J. Fiore of the CDC's Influenza Division.
▸ Group 1-Pregnant women. They have been found at higher risk for complications from seasonal influenza in past pandemics, and several deaths have been reported among pregnant women during the current 2009 pandemic. Vaccination of pregnant women also is seen as a way to potentially protect infants who cannot be vaccinated, via transfer of maternal antibodies to newborns.
▸ Group 2-Household contacts and caregivers for infants younger than 6 months of age. The aim is to provide a possible “cocooning effect,” providing indirect protection for young infants who cannot be vaccinated but are at higher risk for influenza-related complications.
▸ Group 3-Health care personnel and emergency medical personnel (including emergency medical technicians, firefighters, and others whose jobs involve routinely providing emergency medical care in communities). These individuals are seen as a potential source of infection for vulnerable patients. Increased absenteeism could reduce the health care capacity.
▸ Group 4-Children and adults from 6 months through 24 years of age. Children have the highest incidence of illness, and “explosive” outbreaks in schools have been a prominent feature of the spring 2009 epidemiology of the novel influenza A (H1N1). Children younger than 5 years of age are at the highest risk for hospitalization, and are sources of infection for the community and in schools. Moreover, illness in children keeps parents home from work. Young adults also have high attack rates and are seen as vectors.
▸ Group 5-Adults aged 25-64 years with certain medical conditions that place them at greater risk for influenza-related complications. These include chronic pulmonary, cardiovascular, renal, hepatic, cognitive, neuromuscular, hematologic, and metabolic disorders, as well as immunosuppression caused by medications or HIV infection. About 70% of adults hospitalized thus far with novel H1N1 infections had one of these conditions.
If vaccine demand exceeds availability, subgroups of the larger group, totaling 42 million people, should receive priority. The first subgroups—pregnant women and household and caregiver contacts for infants younger than 6 months of age—remain unchanged as a priority. The next subgroups include health care and emergency personnel in direct contact with patients; children aged 6 months through 4 years of age; and children with chronic medical conditions.
When vaccine availability is sufficient at the local level to routinely vaccinate initial target populations, a decision should be made in cooperation with state and local health authorities to vaccinate healthy adults aged 25-64 years first, then individuals aged 65 years and older. The last recommendation, in contrast to seasonal influenza vaccination recommendations, reflects the fact that older individuals thus far have been at lower risk for the novel influenza A H1N1 virus.
New recommendations were needed, Dr. Fiore said, because the federal government's 2007 pandemic vaccine priority guidance had been developed for the scenario of a severe pandemic with the potential for social disruption of critical infrastructure. The ACIP's Influenza Working Group concluded that current epidemiologic and immunologic evidence, combined with updated information on vaccine supply and availability timelines, indicated a need to revise recommendations that had been made during prepandemic planning.
In drafting the document that ACIP voted on, the working group assumed the following: that the severity of illness and groups at higher risk for infection or complications will be similar to what has already been observed; that the safety profile and antigen content of novel H1N1 vaccines will be similar to that of seasonal vaccine; and that adequate supplies of licensed unadjuvanted vaccine can be produced for all by approximately February 2010 but that enough vaccines for all will not be available before the next pandemic wave, expected this fall.