Influenza Season 2009-10

If it seems that the 2008-09 influenza season was unusually long, perhaps it is just that we have had artificially short influenza seasons in past years. This year was marked by a generous supply of influenza vaccine, expanded recommendations from the CDC for who should receive vaccine, and a push to continue providing vaccine after the initial fall period traditionally associated with "flu" season. The year was also remarkable by the detection of a new strain of influenza A virus that poses its own set of questions about future vaccine availability, administration, and acceptance by the public in the fall. Historically, most influenza vaccine is administered during the months of October through December, even though the flu season may not peak until the early spring. Much of the testing for novel H1N1 was conducted in the month of May, during which time it was clear that there was still significant seasonal or non-novel influenza disease in the community.

For the 2009-10 season, progress is under way to manufacture the trivalent vaccine for seasonal influenza that will contain A/Brisbane/59/2007 (H1N1)-like, A/Brisbane/10/2007 (H3N2)-like, and B/Brisbane/60/2008-like antigens. Compared to the 2008-09 Northern Hemisphere influenza vaccines, only the B strain has changed.

While information about vaccine development for the novel H1N1 flu is fluid and subject to change, the reference strains have been sent by the CDC to manufacturers who are initiating processes to create master seed strains to prepare for manufacturing pilot lots. One manufacturer has already successfully run the first batch of the vaccine. A decision to develop and manufacture a vaccine is independent from the decision to administer a vaccine. The decision to administer will be based on the evolving epidemiology over the summer and fall as data from the Southern Hemisphere are collected to assess the virulence and attack rate of the virus.

It is likely that a new vaccine would require two doses. This means that some people will be recommended to receive three immunizations: one seasonal plus two novel H1N1. Children ages 6 months to 8 years who have not previously received influenza vaccine should receive two doses of vaccine separated by more than four weeks. Nationally, providers will be encouraged to use their local immunization registries to keep track of doses for clients and to manage inventory. In San Diego, the San Diego Regional Immunization Registry is a web-based system that is available to all interested practices and is currently used by approximately 200 medical facilities that administer immunizations, including public health centers, community health centers, and private medical practices.

One of the interesting results of the heightened media coverage for novel H1N1 flu was new attention to the fact that more than 36,000 deaths annually in the United States are attributed to seasonal influenza. To try to impact this, the CDC has continued to expand the target populations for whom seasonal influenza vaccine is recommended. Beginning with the 2008-09 season, all children aged 6 months to 18 years of age should be vaccinated against influenza annually. Children typically have the highest attack rates during community outbreaks of influenza and serve as a major source of transmission within communities. According to the CDC, if sufficient vaccination coverage among children can be achieved, there may be the indirect effect of reducing influenza among persons who have close contact with children, thereby reducing the overall transmission within communities. The vaccine is considered to be safe and effective for children, and may help to reduce school absenteeism, decrease antibiotic use and medical visits, and reduce lost days of work for parents.

A frequent topic of discussion among immunization specialists is how to increase the number of healthcare personnel (HCP) who receive annual flu vaccine. Recent data from the San Diego Immunization Branch random digit dialing (RDD) survey indicate a plateau at a little over 50 percent of HCP who receive annual flu vaccine. While this percentage may be higher than the national average, there is much room for improvement. All HCP, as well as those in training for healthcare professions, should receive annual flu vaccine. Physicians can set the tone in their practices by having themselves vaccinated and making vaccine available to all office and clinical staff members. In addition to HCP, other groups who can transmit influenza to high-risk persons that should be vaccinated include employees of assisted living and other residences for persons in groups at high risk, persons who provide home care to high-risk individuals, and household contacts (including children) of persons at high risk.

Traditional groups recommended to receive the seasonal influenza vaccine include persons over 50 years of age and persons with chronic medical conditions such as heart disease, diabetes, or lung disease. According to the CDC 2008-09 Influenza Prevention and Control Recommendations (www.cdc.gov/flu/professionals/acip/specificpopulations.htm), other specific groups who should receive influenza vaccine include:

1. Close Contacts of Immuno-compromised Persons: Close contacts, including HCP, should be vaccinated to reduce the risk of influenza transmission to persons who are at risk for influenza complications but might have insufficient responses to vaccination.
2. Pregnant Women: Pregnant women are at risk for influenza complications.
3. Breastfeeding Mothers: Vaccination is recommended for women who are contacts of infants and children younger than 5 years of age. Breastfeeding is not a contraindication for vaccination, and women who are breastfeeding can receive either TIV or LAIV unless contraindicated because of other medical conditions.
4. Travelers: Any traveler who wants to reduce the risk of influenza infection should get vaccinated at least two weeks before departure if they did not receive flu vaccine during the regular season if they are going to the tropics, traveling with an organized tourist group, or traveling to the Southern Hemisphere during April through September.

Finally, the influenza vaccine is recommended for anyone who wants to reduce the risk of contracting or transmitting influenza.

The San Diego Immunization Branch looks forward to working with its community partners to promote influenza vaccine. Additional information about seasonal and novel H1N1 will be shared as it becomes available. For information about using the registry to help manage the upcoming influenza season, or additional information about vaccines across the lifespan, please go to www.sdiz.org.

San Diego County Health Statistics

• The percentage of healthcare workers in San Diego who receive influenza vaccine is 61. (Source: San Diego County year-round random-digit-dial telephone survey, 2007-08.)
• The percentage of high-risk adults ages 18-64 who receive influenza vaccine is 50.8. (Source: San Diego County year-round random-digit-dial telephone survey, 2008-09.)
• In San Diego, it is estimated that 76.5 percent of seniors (age 65 and over) received the influenza vaccine during the 2008-09 influenza season. This leaves approximately 83,498 seniors who were not protected against influenza. (Source: San Diego County year-round random-digit-dial telephone survey, 2008-09.)

To request additional health statistics describing health behaviors, diseases, and injuries for specific populations, health trends and comparisons to national targets, please call the County's Community Health Statistics Unit at (619) 285-6479. To access the latest reports, data, and data links, go to www.sdhealthstatistics.com.