Sep 26, 2008 (CIDRAP News) – Surveys indicate that recommendations to immunize small children against influenza have been slow to catch on, while flu immunization for adults was somewhat slow to recover from a setback caused by a vaccine shortage 4 years ago, according to the Centers for Disease Control and Prevention (CDC).
A national survey found that only about 21% of children 6 to 23 months old were fully vaccinated in the 2006-07 flu season, 2 years after the CDC formally recommended immunization of the age-group, the CDC reported.
In addition, surveys conducted at eight sites around the country indicated that only 16.5% of children between 24 and 59 months old were fully vaccinated last season, the agency said. The CDC first recommended flu vaccination for that age-group in 2006.
For adults, a national survey showed that flu immunization coverage in the 2006-07 season increased from the previous year but still did not quite match the levels of 2003-04, the season before problems at one vaccine manufacturer cut the expected flu vaccine supply nearly in half, the agency said.
The survey results are presented in today's issue of Morbidity and Mortality Weekly Report (MMWR).
Low coverage in small children
The CDC assessed flu immunization of 6- to 23-month-old children with the National Immunization Survey (NIS), an ongoing, random telephone survey of households with children between 19 and 35 months old, combined with a follow-up mail survey of vaccination providers. Respondents were asked if the children were immunized between September and December of 2006.
The survey, covering all 50 states, drew a response rate of 64.9%. Provider vaccination records were obtained for 9,710 children who met the age criteria. Of these, 31.8% had received one or more doses of flu vaccine, and 21.3% were fully vaccinated (meaning they either had received two doses during the flu season or had received at least one dose before September 2006 and one dose between September and December).
Neither of these percentages marked a significant increase from the previous season, the report says. Coverage varied widely by state, ranging from 8.6% in Mississippi to 47.6% in Rhode Island.
To examine immunization coverage in children from 6 through 59 months old in the 2007-08 season, the CDC analyzed data from its eight immunization information system (IIS) sentinel sites: parts of Arizona, Colorado, Michigan, Oregon, Wisconsin, and Minnesota, plus all of North Dakota and New York City. These sites received supplemental funds for meeting certain criteria, including enrollment of more than 75% of child vaccine provider sites in the IIS.
The CDC found that on average for the eight sites, only 16.5% of children 24 to 59 months old were fully vaccinated, while 22.2% had one or more vaccine doses (full vaccination was defined slightly differently in 2007-08 than in previous seasons).
Among children in the 6- to 23-month age-group, an average of 22.1% were fully vaccinated and an average of 40.8% had had one or more doses, the report says.
The CDC also looked at the number of vaccinations per week and found that the average percentage of total doses given each week increased steadily from Sep 17 through Nov 17. For the 6- to 23-month-old group, fewer than 18% of doses were administered after December; for the older group, fewer than 13%.
The report on the national findings for children aged 6 to 23 months says that vaccination coverage for other newly recommended infant vaccines has reached about 75% within 7 years. The low flu vaccination coverage suggests that factors unique to flu are at work, including the need for annual vaccination, difficulty in vaccinating so many children in a short time, uncertainties in vaccine distribution at the local level, and "a lack of parental or provider confidence or interest in influenza prevention through vaccination."
"The continuing low influenza vaccination coverage described in this report underscores the need to identify innovative strategies for increasing influenza coverage among young children," the article says.
Vaccine shortage left its mark
The CDC assessed flu vaccination coverage in adults by means of the Behavioral Risk Factor Surveillance System (BRFSS), an ongoing, state-based telephone survey that collects data from about 400,000 civilians nationwide. In interviews conducted between February and August, respondents were asked if they had been immunized in the previous 12 months.
Immunization rates reported for the various age and risk groups were as follows:
- 18- to 49-year-olds: those with high-risk conditions, 35.1%; all others, 23.4%
- 50- to 64-year-olds: overall, 42%; those with high-risk conditions, 54.2%; those without high-risk conditions, 37.9%
- Those 65 and older: 72.1%
For all the age-groups, coverage was significantly higher for non-Hispanic whites than for most other ethnic groups.
"Compared with the previous season, influenza vaccination coverage significantly increased during the 2006-07 season among all adult groups for whom vaccination is recommended, but has not yet matched 2003-04 season coverage nor achieved the Healthy People 2010 target of 60% for persons aged 18-64 years with high-risk conditions" and 90% for those 65 and older, the CDC says.
When the vaccine supply ran short in 2004-05, the CDC recommended that healthy people aged 50 to 64 not be a priority group for vaccination, according to the report. As a result, coverage dropped by about half in that group, to 21.8%; it also dropped for other adult groups that still had priority.
Coverage partly rebounded in 2005-06 and improved further in 2006-07, to levels close to those before the shortage, the CDC reports. However, the rate for 50- to 64-year-olds with high-risk conditions was still 4.6 percentage points below the 2003-04 level.
CDC. Influenza vaccination coverage among children aged 6-23 months—United States, 2006-07 influenza season. MMWR 2008 Sep 26;57(38):1039-43 [Full text]
CDC. Influenza vaccination coverage among children aged 6-59 months—eight immunization information system sentinel sites, United States, 2007-08 influenza season. MMWR 2008 Sep 26;57(38):1043-6 [Full text]
CDC. State-specific influenza vaccination coverage among adults—United States, 2006-07 influenza season. MMWR 2008 Sep 26;57(38):1033-9[Full text]