Flu Vaccine Supply Rebounds but Immunization Rates Don't

ATLANTA, Sept. 24 -- Influenza vaccination rates have not rebounded after widespread vaccine shortages in the 2004-2005 flu season, CDC investigators said.

Compared with the 2003-2004 season, vaccination rates were down 3.8 to 8.6 percentage points in the 2005-2006 flu season, reported Peng-Jun Lu, Ph.D., of the CDC, and colleagues in the Sept. 21 issue of the Morbidity and Mortality Weekly Report.

Vaccination coverage declined significantly across each age and risk group, but was most dramatic among healthy adults ages 50 to 64, whose vaccination coverage was 8.6 percentage points lower.

That decline was particularly worrisome because current guidelines recommend annual flu shots for that group as well as for at-risk adults younger than 50 and persons 65 or older.

Those priorities were reshuffled by a vaccine shortage in 2004-2005, which moved healthy people ages 50 to 64 to the back of the flu shot priority line.

The most recent data, therefore, indicate "a possible lingering effect on coverage caused by the vaccine shortage," according to an editorial note in the same issue.

Comprehensive measures are needed if flu vaccination rates are to recover, Dr. Lu and colleagues said.

For healthcare providers, this means strict adherence to the CDC's recommended adult immunization practices and a willingness to continue vaccinating throughout the flu season, they said.

Improving public awareness and addressing remaining problems in the vaccine supply chain will also be important, they added.

The researchers analyzed data from the Behavioral Risk Factor Surveillance System, a telephone survey conducted in the adult civilian population in all 50 states, the District of Columbia, and U.S. territories.

In 2004, 176,994 individuals were interviewed about influenza vaccination during the months following the flu season; 210,335 were interviewed in 2006.

The CDC recommends annual inoculation for adults younger than 50 primarily if they have a condition increasing their risk for serious complications of infection. These high-risk conditions included diabetes and asthma in 2004 with the addition of myocardial infarction and coronary heart disease in 2006.

In the 2005-2006 season, only 30.5% of these younger adults with high-risk conditions and 18.3% of other younger adults reported getting the flu shot. Vaccination rates ranged from a high of 43.0% in Rhode Island to a low of 19.3% in Nevada.

The vaccination rate for high-risk younger adults was down 5.7 percentage points overall compared with 2003-2004. Variation from state to state was substantial (range -23.1 to 6.1), but declined significantly in 22 states.

Vaccination coverage for adults ages 50 to 64 rebounded even less.

In this group, vaccination rates for the 2005-2006 season were 36.6% overall, ranging from 49.9% in South Dakota to 23.8% in Florida. The rate was higher for survey respondents with high-risk conditions than for those without them (48.4% versus 32.2%).

This represented a 7.1 percentage point drop from 2003/2004 to 2005/2006 for adults age 50 to 64 with high-risk conditions and 8.6-percentage point lower rate for healthy adults in this age range.

Individuals over age 65 had the highest flu shot rates, 69.3% overall in 2005-2006, ranging from 78.8% to 58.3% in individual states.

This group, which was considered a priority group for flu shots during the 2004-2005 shortage, also showed the least change in vaccination coverage from the 2003/2004 season to the 2005-2006 season of all the age groups, posting only a 3.8-percentage point decline overall.

Although response rates to the state surveys were relatively low-averaging only around 50% -- the results clearly showed vaccination coverage "did not return to levels observed before the vaccine shortage of 2004-2005," Dr. Lu and colleagues said.

This was despite an adequate supply of flu vaccine in 2005-2006, "although the distribution of vaccine from one manufacturer was delayed, which could have contributed to decreases in coverage," the editorial note acknowledged. (See: CDC Declares No Shortage of Flu Vaccine, Appearances Not Withstanding)

If this trend continued during the 2006/2007 influenza season, less than 50% of the approximately 218.1 million persons recommended for vaccination (73.1% of the population) likely received their annual flu shot, the editorial note concluded.