Brief analysis of a risk communication error:
The CDC reports its newest estimate of influenza vaccine efficacy:
50-70% in healthy adults under 65
By Jody Lanard M.D. (posted on October 25 2011, 1:30 pm EDT)
On October 12, the U.S. CDC updated its estimate of influenza vaccine effectiveness (written for health care professionals), based on randomized controlled studies published in 2009 and early 2010.
The most notable datum in the update:
Flu Vaccine Effectiveness: Questions and Answers for Health Professionals (October 12 2011)
>How well do inactivated influenza vaccines work in randomized control trials?
>As noted above, effectiveness varies with vaccine match and the age and immune function of the recipient. In general, the greatest benefits of influenza vaccines have been reported in randomized controlled trials (RCTs) conducted among healthy adults. For example, recent RCTs of inactivated influenza vaccine among adults under 65 years of age have estimated 50-70% vaccine efficacy during seasons in which the vaccines' influenza A components were well matched to circulating influenza A viruses (Beran et al., 2009, 2006-2007 season; Jackson et al., 2010, 2005-2006 season; Monto et al., 2009, 2007-2008 season). As vaccine efficacy from a randomized clinical trial is the gold standard for how well a vaccine actually works, vaccine effectiveness estimates obtained from observational studies can equal, but not exceed, estimates of efficacy.<
This updates the CDC’s previous estimate of 70% to 90% efficacy, based on older studies.
Here's the risk communication error:
The October 12 2011 update does not mention the previous estimate, or highlight that “50-70%” in healthy adults under 65 is a rather dramatic downward change. The update only notes that the estimate is based on “recent RCTs”.
And the CDC did not issue a heads-up to journalists highlighting the new, much lower estimate of efficacy.
As of noon on October 25th, no medical or other journalists appear to have reported this new information.
One excellent news scan that I follow, from the Center for Infectious Disease Research and Policy (CIDRAP) at the University of Minnesota, reported on the CDC’s new update, in an item entitled “CDC backgrounder helps health providers interpret flu vaccine effectiveness”, without mentioning the updated estimate of flu vaccine efficacy.
On October 13, CDC updated its parallel page for general readers:
Vaccine Effectiveness - How Well Does the Flu Vaccine Work? (October 13, 2011)
The update for general readers does not mention the new estimate at all.
Until February 2011, the update for general readers stated:
"Past studies have shown in years when the vaccine viruses and circulating viruses are well-matched, the vaccine can reduce the chances of getting the flu by 70% to 90% in healthy adults.” (see this version of the page as it appeared in December 2010 on the CDC website.)
On February 25, 2011, CDC eliminated that datum from the update for general readers, and stated:
“CDC is currently reviewing recently published studies on VE to update existing estimates." (see this version of the page, updated on February 25 2011, as it appeared in April 2011 on the CDC website.)
And on October 13 2011, one day after updating the report for health professionals, the CDC updated its flu vaccine effectiveness page for general readers without including any efficacy estimates for healthy adults under 65: not the old “70-90%”; not the new “50-70%.”
Comment:
From my perspective as a risk communication analyst, I hypothesize that the CDC did not want to draw attention to its new lower estimate of flu vaccine efficacy – or to the fact that CDC’s experts have known about the new studies behind the new estimate for almost two years.
My ongoing study of influenza vaccine communication over the years – particularly analysis of annual flu vaccine promotion campaigns every year in both hemispheres – strongly suggests to me that many public health officials, at the U.S. CDC and other national health agencies, routinely convey the impression that influenza vaccine is more effective than it is.
I believe they convey this mis-impression for pro-social, pro-public health reasons – including their fear that if people learned that the flu vaccine is not very effective (compared with most other vaccines in common use), they would be even less inclined to get vaccinated.
But as a risk communication expert, I think they are wrong to do this.
I hypothesize – but cannot prove – that overstating the benefits of any vaccine exacerbates the atmosphere of vaccine skepticism and distrust that so worries those of us (myself included) who strongly support the CDC’s recommended use of vaccines.
For more risk communication analysis related to vaccine communication, see:
Convincing Health Care Workers to Get a Flu Shot – Without the Hype! (January 2009)
And
Trust the Public with More of the Truth (October 2009)
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