Tuesday, March 31, 2015

CDC Study: Lives Saved By the Flu Vaccine



# 9887


Given this year’s poor performance, and resultant bad press, from the seasonal flu shot it is understandable that the CDC, and other public health entities, would want to `rehabilitate’ the flu vaccine’s recently maligned reputation.  Particularly since - even in a `bad-match’ year - the flu vaccine can save lives.


The flu shot – while far from perfect – has an excellent safety profile, and most years provides a moderate degree of protection against seasonal influenza.  


As regular readers of this blog already know, I get one every year. And while I sometimes worry that the benefits (and effectiveness) of the flu vaccine are oversold, flu vaccines remain our best protection against a virus that is estimated to kill a half million people around the globe each year.    


I often liken it to wearing a seatbelt – something that cannot guarantee you’ll walk away from a head-on collision - but it does definitely improve your chances.


Flu shots do not, however, protect against non-influenza respiratory viruses. And this year – due to the late arrival of a `drifted’ H3N2 virus (see CDC HAN Advisory On `Drifted’ H3N2 Seasonal Flu Virus) – it didn’t do very well against influenza either.


Seasonal flu VE (Vaccine Effectiveness) ratings, which normally run 50%-60%, came in at a disappointing 18% according to the CDC’s Updated Estimated Seasonal Flu Vaccine Effectiveness report.

Given the speed by which influenza viruses mutate, and the need for six months lead time to create, produce, and deploy the vaccine, it is inevitable that some years the vaccine will miss its mark. 


Our reliance on what is essentially 50 year-old vaccine production technology is a bottleneck we’ve discussed often (see Revisiting CIDRAP’s - The Need For Better Flu Vaccines), and one that could really come to haunt us should a pandemic virus emerge. 


Showing that even a modestly effective vaccine can save lives, we have the following CDC sponsored study published in the journal Vaccine, followed by a press statement from the CDC.


Deaths averted by influenza vaccination in the U.S. during the seasons 2005/06 through 2013/14

Ivo M. Foppaa, b, , , , Po-Yung Chenga, b, Sue B. Reynoldsa, c, David K. Shaya, Cristina Cariasd, e, Joseph S. Breseea, Inkyu K. Kima, b, Manoj Gambhird, Alicia M. Frya



Excess mortality due to seasonal influenza is substantial, yet quantitative estimates of the benefit of annual vaccination programs on influenza-associated mortality are lacking.


We estimated the numbers of deaths averted by vaccination in four age groups (0.5 to 4, 5 to 19, 20 to 64 and ≥65 yrs.) for the nine influenza seasons from 2005/6 through 2013/14. These estimates were obtained using a Monte Carlo approach applied to weekly U.S. age group-specific estimates of influenza-associated excess mortality, monthly vaccination coverage estimates and summary seasonal influenza vaccine effectiveness estimates to obtain estimates of the number of deaths averted by vaccination. The estimates are conservative as they do not include indirect vaccination effects.


From August, 2005 through June, 2014, we estimated that 40,127 (95% confidence interval [CI] 25,694 to 59,210) deaths were averted by influenza vaccination. We found that of all studied seasons the most deaths were averted by influenza vaccination during the 2012/13 season (9398; 95% CI 2,386 to 19,897) and the fewest during the 2009/10 pandemic (222; 95% CI 79 to 347). Of all influenza-associated deaths averted, 88.9% (95% CI 83 to 92.5%) were in people ≥65 yrs. old.


The estimated number of deaths averted by the US annual influenza vaccination program is considerable, especially among elderly adults and even when vaccine effectiveness is modest, such as in the 2012/13 season. As indirect effects (“herd immunity”) of vaccination are ignored, these estimates represent lower bound estimates and are thus conservative given valid excess mortality estimates



CDC Study: Flu Vaccine Saved 40,000 Lives During 9 Year Period

March 30, 2015 – The seasonal flu vaccine prevented more than 40,000 flu-associated deaths in the United States during a nine year period from 2005-2006 through 2013-2014 according to estimates in a new study published in the journal Vaccine. This estimate represents a little less than a one-quarter (22%) reduction in the deaths that would have occurred in the absence of flu vaccination during that time. CDC has estimated previously that seasonal flu-associated deaths in the United States range between 3,000 and 49,000 people each year.

Estimates from the study showed that the majority of the flu-associated deaths prevented—nearly 89 percent (88.9%)—were in people 65 years of age and older. Next to older people, young children 6 months through 4 years of age benefitted most from flu vaccine in terms of the percentage of deaths averted. Children younger than 5 years old and adults 65 years of age and older are at high risk of serious flu complications and typically account for the majority of flu-associated deaths and have the highest flu-associated hospitalization rates.

The study included a breakdown of deaths prevented by season. The most deaths were prevented during the 2012-2013 season, when nearly 9,400 deaths were prevented by vaccination, despite modest estimated vaccine effectiveness that season. Like the current 2014-2015 flu season, H3N2 viruses circulated predominantly during the 2012-2013 season.

The fewest deaths prevented by flu vaccination occurred during the 2009 pandemic. Researchers estimated that 222 deaths were prevented by vaccination that season. Study authors attributed this to the fact that 2009 monovalent pandemic vaccine did not become widely available until well after the peak of influenza illness had occurred. Flu activity during the pandemic was dominated by 2009 H1N1 virus circulation, with almost no seasonal viruses being detected during that time.

To conduct the study, researchers applied statistical modeling with U.S. age-group specific estimates of flu-associated excess deaths, monthly flu vaccination coverage estimates, and summary seasonal flu vaccine effectiveness (VE) estimates.

Overall, the findings from the study continue to support the benefits of flu vaccination and suggest that both increased flu vaccination coverage and increased flu vaccine effectiveness would help to prevent more flu-associated deaths.

The article is available online from the Vaccine journal’s website.


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