Flu season is about to be upon us. I’ve written about this before, but it’s been a few years, so I thought I’d update some of the evidence (with my thanks to Juan Gervas, MD for compiling a nice list of relevant studies). This, in the face of the recent CDC proclamation that 80,000 people died of the flu last season. The implication is, of course, that everyone must get their flu shot.
How effective is the flu shot?
There are different ways to measure this. The CDC reported that the shot has been effective in reducing outpatient visits for the flu by about 40% in the last few years. But this is a relative decrease. What are the absolute numbers? A Cochrane review of 52 trials over 40 years found that the absolute decrease went from 2.3% to 0.9% of adults who caught the flu, or 1.4% total (NNT 71). There was no evidence that the vaccine reduces missed days from work, hospitalizations, or deaths. Similar results were found in a separate review of the vaccine in children.
How many people in the U.S. die of the flu each year?
The CDC historically states that around 30-40,000 people die each year from the flu, but this is clearly exaggerated. A review of actual death certificates found that the actual number was closer to 1,000. A paper discussed in the next section came to a similar conclusion. One of the contributing factors to the exaggeration is that an observed increase in chronic disease deaths is attributed to the flu. A recent study in NEJM for the first time, to my knowledge, actually got flu titers in hospitalized adults to try to prove causality. They found an increased risk of myocardial infarctions in people with confirmed respiratory infections, but not deaths, and RSV and other viruses were also implicated. I believe this is the first study that more proves that an increase in exacerbations in some non-respiratory chronic diseases is likely caused by the flu.
Do flu shots save lives?
Basically, no. There have been several reviews of this over the years. The above-mentioned Cochrane reviews in adults and children are 2 of them. A review in JAMA of infectious disease mortality found a non-significant increase in flu mortality from 1980 to 2014, a period of greatly increased uptake of the flu vaccine. It also points out that the overall number of flu deaths is great exaggerated (see Table in article). Of the 17.3/100,000 mortality rate of pneumonia and flu, only 1.4/100,000 were from the actual flu virus.
Is the flu vaccine cost-effective?
It entirely depends on the assumptions used to do the analysis. A cost-effectiveness analysis (CEA) published in the Annals of Internal Medicine concluded that flu shots save money. However, their model assumed a population of 8.3 million people and that the number of lives saved would be between 1,468 and 2,051 in one year. As I described previously, studies of all U.S. death certificates identify around 1,000 with flu listed as the cause of death, so it is apparent that these authors used the mostly wildly optimistic assumptions of the effectiveness of the vaccine.
Another study made similar assumptions about the efficacy of the vaccine, assuming that the vaccine prevented deaths in 2-7% of the non-elderly population and 16% of the elderly population (if I’m interpreting their table correctly). Therefore, the vaccine was estimated to be cost-saving.
Another study found that the vaccine was cost saving for high-risk groups and had an incremental cost-effectiveness ratio (ICER) of $8,000-$52,000 for other patient groups. They assumed a vaccine effectiveness of 60%-69%. They did not explicitly state their assumptions about deaths, though it appears they assumed that if the vaccine was effective for 60-69% of people, then they didn’t die. Both of these assumptions are contradicted by the other lines of evidence already discussed.
Other findings:
The effect of health care workers forced to get flu shots on decreasing patient harm is greatly exaggerated: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0163586
The flu vaccine becomes less effective with repeated vaccinations and does not prevent household transmission of the flu virus: https://academic.oup.com/cid/article/56/10/1363/404283
There was an increased risk of developing narcolepsy in Northern European countries from receiving a flu shot, by a factor of 5-14 fold in children and 2-7 fold in adults. The overall risk was estimated to be about 1 in 18,000 vaccinated people. This may be related to a single batch from one manufacturer. https://www.sciencedirect.com/science/article/pii/S1087079217300011
Other systematic reviews have pointed out the large gap between the public policy enthusiasm for widespread flu vaccination vs. the evidence of its actual effectiveness: https://www.bmj.com/content/333/7574/912
Conclusions
Because there are no good RCTs of flu vaccination, the truth is no one knows how effective the flu shot is or how cost-effective it is. Using probably wildly optimistic assumptions of the effectiveness of the vaccine to prevent deaths, it may actually save money. On the other extreme, it could have a very high ICER if the only real benefit is a 40% drop in office visits for the flu, with no lives saved.
The other truth is that we’ll probably never know, because no politician would ever have the courage, in the U.S. at least, to call out this potentially large waste of national resources and pay for a proper study.
Any data on “Effect of using Flu vaccine rate as a phony quality measure on the well-being and income of family physicians”?
No, but I’ll keep my eyes open for it. Of course, I don’t think the flu vaccine rate is much different from any other phony quality measure of family physicians.