Flu vaccine mostly went to priority groups, CDC says

Mar 31, 2005 (CIDRAP News) – Influenza vaccination coverage among people in high-risk groups this season was similar to levels in past years, signaling that the government's effort to make the most of the limited vaccine supply paid off, federal health officials reported today.

Two-thirds of the vaccine doses administered from the beginning of the flu season through January went to people in priority groups, whereas about half of all doses went to those groups in the previous year, the Centers for Disease Control and Prevention (CDC) says. The information appears in the Apr 1 issue of Morbidity and Mortality Weekly Report.

In addition, the altruism of healthy adults who skipped their flu shots, "saving vaccine for people who need it more," according to a phone survey, led to about 17.5 million doses being freed for people in priority groups, the CDC reports.

"Despite an unexpected and substantial vaccine shortfall, coverage levels among adults in the original influenza vaccine priority groups were similar to historical demand . . . thereby suggesting the effectiveness of prioritization," the article says.

The nation lost about half of its anticipated flu vaccine supply last October because of contamination at a Chiron Corp. plant in the United Kingdom. The CDC responded by recommending that available doses go to people at increased risk for flu complications, including the elderly, healthcare workers with patient contact, pregnant women, people with chronic medical conditions, children aged 6 to 23 months, people caring for babies younger than 6 months, and children on chronic aspirin therapy. (In late December, healthy people aged 50 to 64 and household contacts of people at high risk were added to the priority list, because of declining demand among other groups.)

The findings come from the CDC's nationwide Behavioral Risk Factor Surveillance System (BRFSS) telephone survey. Because it was the first year certain questions about vaccination were used, the results had to be measured against findings in two other surveys, the 2003 National Immunization Survey (NIS) and the 2003 National Health Interview Survey (NIHIS). The CDC cautioned that only limited comparisons can be made among those surveys.

Here's how the 2004-05 BRFSS and 2003 NHIS findings on vaccination rates compared:

• Those aged 65 and older: 62.7% and 65.5%
• Healthcare workers with patient contact: 35.7% and 40.1%
• Pregnant women and people with chronic conditions: 25.5% and 34.2%
• Healthy people aged 18 to 64: 8.8% and 17.8%

About 48.4% of children aged 6 to 23 months received flu shots this season, the first time the CDC formally recommended flu shots for that age-group. In addition, 34.8% of children aged 2 through 17 with high-risk conditions were vaccinated, which was much higher than the 12% coverage among children in that age-group who were not in a priority group.

The Chiron vaccine woes didn't affect vaccines for children younger than 2 years. But the outcome remains significant because it "suggests how quickly physicians and parents can adopt a new disease-prevention guideline," the CDC says.

"Despite the shortfall of inactivated influenza vaccine, the level of coverage achieved among those groups prioritized in 2004-2005 appears to be similar to historical coverage," the report states. "Additional guidelines for prioritization of influenza vaccination in the event of a future influenza vaccine shortfall are in development and should assist with efforts to maximize the use of available vaccine."

Limitations of the BRFSS data include potential self-reporting error, exclusion of people without land-line telephones, exclusion of certain vaccine priority groups (i.e., institutionalized adults and adult caretakers of babies younger than 6 months outside the home), and exclusion of vaccinations that took place after the Feb 1-27 survey.

CDC: Estimated influenza vaccination coverage among adults and children—United States, September 1, 2004–January 31, 2005. MMWR 2005 Apr 1;54(12):304-7 [Full text]