Flu Shots Effective Half the Time For Winter 2004/2005, According to New Poll of U.S. Adults

ust over a quarter (27%) of U.S. adults claim to have had a flu shot before the winter of 2004/2005, when there was, initially, a shortage of available vaccine. This is a significant decline from the 35 percent who claimed to have had a flu shot for the previous winter of 2003/2004. Flu vaccines don’t prevent all flus, but those who received flu shots for this winter were much less likely to get the flu (13%) than those who did not have flu shots (23%). This suggests that the vaccine was effective about half the time.

Experts on the flu say that it is easy to confuse the flu with other infections, so many people who believe that they had the flu may not have actually had it. However, a large 82 percent majority (whether or not they had received flu vaccine shots) of those who believe they had the flu say they are certain they had it; but only a third (34%) visited a doctor who diagnosed the flu.

These are some of the results of a nationwide Harris Poll of 2,630 U.S. adults surveyed online by Harris Interactive^® between March 8 and 14, 2005.

Other interesting results of this research include:

• The differences in the prevalence of flu between those who had, and did not have, flu shots were similar for each of the last two winters (14% vs. 21% in 2003/2004 and 13% vs. 23% in 2004/2005).
• Three times as many adults tried to get flu shots but didn’t get them this last winter (16%) as compared to the previous winter (5%).
• Older people are more likely to have received flu shots this last winter (2004/2005). Fully 57 percent of people aged 65 and over had flu shots compared to only 9 percent of people aged 18–24.
• About one-third of those who tried and failed to get flu shots subsequently got what they believe was the flu (5% out of 16%, of all adults).

Base: All Adults

Note: Percentages may not add to 100% due to rounding.

"Thinking back to this winter just ending…?"

Q. "Did you have a flu vaccine shot before this winter?"

Q. "Did you try and get a flu shot but did not get one because of the flu vaccine shortage?"

Base: All Adults

The Harris Poll^® was conducted online within the United States between March 8 and 14, 2005 among a nationwide cross section of 2,630 adults aged 18 and over, of whom 698 got a flu shot before the winter of 2004/2005. Figures for age, sex, race, education, region and household income were weighted where necessary to bring the sample of adults into line with their actual proportions in the population. Propensity score weighting was also used to adjust for respondents’ propensity to be online.

In theory, with probability samples of this size, one could say with 95 percent certainty that the results have a sampling error of plus or minus 2 percentage points. Sampling error for the various sub-sample results is higher and varies. Unfortunately, there are several other possible sources of error in all polls or surveys that are probably more serious than theoretical calculations of sampling error. They include refusals to be interviewed (non-response), question wording and question order, and weighting. It is impossible to quantify the errors that may result from these factors. This online sample is not a probability sample.

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Q752, Q755, Q760, Q765