In interim efficacy data for the 2016-2017 flu season, the current vaccine is proving 48% effective, the CDC reports.1
The overall efficacy was based on efficacy against influenza A and influenza B virus infection associated with acute respiratory illness requiring medical attention. As of Feb. 17, 2017, most influenza infections were being caused by A (H3N2) viruses. Vaccine efficacy specifically against H3N2 was estimated to be 43%, but efficacy rose to 73% against the circulating B virus.
“These interim vaccine efficacy estimates indicate that influenza vaccination reduced the risk for outpatient medical visits by almost half,” the CDC reported.
Historically, a comprehensive review of the literature estimated an overall flu shot efficacy of 59% in healthy adults ages 18 to 64 years.2 Evidence was inconsistent or lacking to determine vaccine efficacy in those ages 2-17 and those over 65.
Of course, the vagaries of antigenic “drift” or more dramatic “shift” of circulating, mutable influenza viruses create an ongoing challenge to making an annual vaccine with a good match. For example, last year’s overall flu vaccine efficacy was 41% against the predominant H1N1 influenza A strain and 55% against circulating B strains.3
While the overall societal benefit is frequently underscored by even partially effective flu vaccines, it is harder to make the case for mandatory immunization of heathcare workers, says Gaston De Serres, MD, the lead author of a recent paper calling mandates into question.4
“It is interesting that most of the organizations and associations that publish support for mandating immunization [in healthcare workers], use data underscoring that influenza is a terrible disease with tens of thousands of deaths annually and hundreds of thousands of hospitalizations,” De Serres says. “Well, that’s irrelevant and will not be affected by the immunization of healthcare workers. The relevant burden of disease [in making an argument for mandated immunization] are only the cases represented by unvaccinated healthcare workers.”
In a political climate where even widely accepted science may be challenged, proponents of mandatory flu shots for healthcare workers should be wary of refuting the findings without clear evidence of vaccination benefits, says Michael Edmond, MD, clinical professor of internal medicine and infectious diseases at the University of Iowa in Iowa City.
As an alternative, flu vaccination should be voluntary, but highly encouraged to get as many healthcare workers immunized as possible, he says.
“But to say that we are going to fire you?” Edmond says. “Over the last 10 years or so there have been years where the vaccine is barely 20% effective — one year it was 10% effective. Are you are going to fire people because they didn’t get a vaccine that is 10% effective? And we can’t even prove if they got it, it would reduce influenza in patients. We would have to have a very tight set of data to take it to that level. I can’t think of another example that is taken to this extreme, without a very high level of evidence to support it.”
REFERENCES
- CDC. Interim Estimates of 2016–17 Seasonal Influenza Vaccine Effectiveness — United States. MMWR 2017;66(6):167–171.
- Osterholm MT, Kelley NS, Sommer A, et al. Efficacy and effectiveness of influenza vaccines: a systematic review and meta-analysis. Lancet Infect Dis 2012;12:36-44.
- CDC. Summary of the 2015-2016 Influenza Season. September 29, 2016: http://bit.ly/2mBlJSI.
- De Serres G, Skowronski DM, Ward BJ, et al. (2017) Influenza Vaccination of Healthcare Workers: Critical Analysis of the Evidence for Patient Benefit Underpinning Policies of Enforcement. PLoS ONE 2017; 12(1): doi:10.1371/journal.pone.0163586.