Health experts are warning that this year’s influenza outbreak could be the worst in a decade. That’s why public health officials are urging almost everyone to get a flu shot. Older people (those over 65) are cautioned that they may have weakened immune systems and are especially vulnerable to the consequences of influenza. They are told that a flu shot will reduce their chances of getting sick, and if they do catch influenza it will be less serious. It’s hard to resist such a pitch. Millions of seniors are signing up for their shots. How good is the evidence to support this public health message?
The most objective organization for analyzing treatments is the Cochrane Collaboration. It is an international network of over 28,000 people from more than 100 countries who scrutinize scientific data from all over the world. The independence and objectivity of the Cochrane reviewers allows them to assess the effectiveness of a variety of treatment strategies in a way that few other groups can match. The Cochrane investigators have carefully analyzed flu vaccines and come up with some startling conclusions.
In 2010 (the most recent analysis) the Cochrane Database of Systematic Reviews published a study titled “Vaccines for preventing influenza in the elderly.” The authors assessed 75 studies. The conclusions:
“The available evidence is of poor quality and provides no guidance regarding the safety, efficacy or effectiveness of influenza vaccines for people aged 65 years or older.”
We don’t know about you, but we find that conclusion shocking. Physicians are told that they are supposed to practice “evidence-based medicine.” That means that they are supposed to rely on solid scientific data before recommending a particular treatment…such as a flu shot. And yet the best experts in the world state clearly that such evidence does not exist to support influenza immunization for those over 65.
What about everyone else? One of the reasons that public health officials also encourage younger people to get a flu shot is that it is supposed to provide “herd immunity.” In other words, if children and healthy adults get a shot, they are theoretically less likely to spread the flu to the most vulnerable in the population, namely older people and infants. So, how good is the evidence that flu shots do something meaningful for healthy adults?
An analysis published in The Lancet Infectious Diseases (Jan. 2012) produced disappointing results. Researchers combed the medical literature for studies published between 1967 and 2011. After reviewing over 5,000 articles they narrowed their evaluation to 31 of the very best studies. These trials actually confirmed influenza infection through culture or a more sophisticated laboratory test. In the gold-standard randomized-controlled trials, the pooled efficacy was 59%. There was surprising variability in effectiveness from year to year. In some years, effectiveness was as low as 16%, while in other years it rose to 76%.
The Cochrane investigators also reviewed all the published studies of flu vaccine effectiveness in healthy adults (people between 16 and 65 years of age). They analyzed 50 studies carried out between 1966 and 2010 (Cochrane Database of Systematic Reviews, Jul 7, 2010). The authors concluded:
“Influenza vaccines have a modest effect in reducing influenza symptoms and working days lost. There is no evidence that they affect complications, such as pneumonia, or transmission.”
Here is the “Plain Language Summary” of the results of their investigation:
“Authors of this review assessed all trials that compared vaccinated people with unvaccinated people. The combined results of these trials showed that under ideal conditions (vaccine completely matching circulating viral configuration) 33 healthy adults need to be vaccinated to avoid one set of influenza symptoms. In average conditions (partially matching vaccine) 100 people need to be vaccinated to avoid one set of influenza symptoms. Vaccine use did not affect the number of people hospitalised or working days lost but caused one case of Guillian-Barré syndrome (a major neurological condition leading to paralysis) for every one million vaccinations. Fifteen of the 36 trials were funded by vaccine companies and four had no funding declaration. Our results may be an optimistic estimate because company-sponsored influenza vaccines trials tend to produce results favorable to their products and some of the evidence comes from trials carried out in ideal viral circulation and matching conditions and because the harms evidence base is limited.”
Yikes! If the primary purposes for getting a flu shot are to avoid getting influenza and reduce the likelihood of developing complications (such as pneumonia) or spreading the virus to other people (such as senior citizens), then there is little evidence that these goals are achieved. If you read the summary carefully, you will discover that even with a perfect vaccine, 33 people would have to be vaccinated for one to person to avoid the flu. In our humble opinion that is not very impressive.
What are we to make of this confusion? The experts plea for better research to determine the true effectiveness of the influenza vaccine, especially in older people. How can public health officials encourage everyone to get a shot without excellent data to support their recommendations? Public health experts are hoping to get 80% of the American public vaccinated against influenza in coming years. People deserve convincing evidence that such an effort will be worthwhile.
This is not to suggest that vaccines in general should come under suspicion. The smallpox vaccine was responsible for the greatest public health achievement of the 20th century, the elimination of this deadly and disabling infection. Providing polio vaccine to all at risk of this virus should lead to a similar accomplishment early in the 21st century. Research evidence as well as experience demonstrates that the benefits of these vaccines greatly outweigh their risks. We’d love to see similar evidence on influenza immunization.
It may be that today’s modern flu vaccines really do work, meaning that they protect 80 to 90 percent of those who get a shot from developing flu symptoms and complications. But we won’t know that until objective research proves it. In the meantime, you are pretty much on your own. Ask your doctor to review the scientific literature to see whether she can find evidence of effectiveness and give you better guidance. We have provided links to the most complete data. We would welcome physician feedback.
We would also love your thoughts about the influenza vaccine. Do you always get a flu shot? Does it protect you? Have you ever gotten a shot only to come down with the flu anyway? Share your story below.