Our guest contributor is Dr. Joshua Goldenberg, a naturopathic physician, professor, researcher, and creator of Dr. Journal Club. He has presented nationally and internationally on evidence-based medicine as well as probiotics and research methodology. Dr. Goldenberg will share with us a 4 part series reviewing the evidence for safety and efficacy of the influenza vaccine in healthy children, healthy adults, the healthy elderly population and high-risk cardiac patients. In part 1 of the series, he will focus on the evidence of the influenza vaccine for children.
The CDC recommends that all individuals 6 months and older get vaccinated against influenza each year. The vaccine itself is designed to prevent true flu not all flu-like illness and is developed based on a ‘best guess’ as to what the circulating strain of the flu virus will be each year. Some years like the 2014-2015 flu season are poor matching years, meaning the best guess was not accurate and the vaccine did not provide much protection against flu, while other years like the 2015-2016 season are good matching years (www.CDC.gov/flu). The benefits of vaccinating healthy children include: reducing the overall number of people with flu, reducing hospital admission, reducing death and complications of elderly folks living with the children, reducing prescribed antibiotics and reducing days missed from school (and work if the parents need to stay home with the kids). We begin our evidence review looking at a Cochrane review for flu vaccines in healthy children.
In this Cochrane systematic review and meta-analysis the authors found 75 studies, 17 of which were RCTs for their review. The authors determined that live vaccines have an amazing relative risk reduction of 80% for preventing true influenza infections. This is based on over 9,000 participants in six RCTs. When you break it out by age we actually see that there is no data on those under two years of age and that for those older than two there is a risk difference (so absolute effect size not relative effect size) of 16% which translates to a number needed to vaccinate of six. So you need to vaccinate six kids with the live vaccine to prevent one case of true flu. With the inactivated influenza vaccine we see a numbers needed to vaccinate of only three but again no data on those under two years of age.
When you expand the question to look at flu-like illness overall not just true flu, the authors found that the live vaccine leads to a relative reduction in flu-like illness of 33% based on eight trials with over 18,000 participants. When you break it out by age you again see no data for those younger than two and a reasonable absolute risk reduction of 8% leading to a numbers needed to vaccinate of 12 to prevent one case of flu-like illness. With inactivated vaccines we see a similar effect size and a numbers needed to vaccinate of eight.
Regarding complications, they found no evidence that flu vaccines impact lower respiratory tract infections such as pneumonia, antibiotic prescriptions, ear infections, or socioeconomic outcomes. There may be an effect on missed school and work but it is based on just one or two trials.
We have some sparsely reported adverse events but these vaccines are extremely safe overall. However, the authors correctly point out that there is a high risk of bias in the safety data and it may be worse than reported.
Considering the fact that the CDC and WHO are recommending that basically everyone on earth get vaccinated due in large part to an attempt to prevent complications, the evidence base is sparse. We basically have no data on complications at all and the little data we have is poor quality and industry sponsored.
Overall I agree with the authors that most of the data that is available that they combined in a meta-analysis is suspect. And indeed for those younger than two years of age we have basically no data. But the evidence that we do have shows that for healthy children the vaccine is efficacious and effective and has excellent numbers needed to vaccinate in my opinion. To quote the authors: “national policies for the vaccination of healthy young children are based on very little reliable evidence.”
Finally, overall it does appear that flu vaccines are very safe. They are administered in the hundreds of millions of doses per year and reports of serious adverse events are sparse and while a couple vaccines have been associated with consistent adverse events they have been pulled from the market quickly.
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Dr. Journal Club is a site for busy integrative medicine professionals who want to learn more about evidence-based medicine and keep up-to-date with the latest clinically relevant research studies. It houses extensive research video summaries that are updated weekly as well as critical evaluation of the medical literature skills videos.