How is 45? Well, that depends on what you are talking about, of course. Eating 45 doughnuts in one sitting is probably not so good. Batting .450 in a Major League Baseball season? That’s good. All-time best good. A flu vaccine that’s 45% effective? That’s certainly not the all-time best. But it’s still better than it was this time last year: 29%.
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The 45% number came from a report released yesterday by the Centers for Disease Control and Prevention (CDC). This report indicated that so far the flu vaccine has been an estimated 45% effective in preventing “influenza-associated medically attended acute respiratory illness.” Ummm, what the who attending a cute illness what? This may seem like a jumble of words if you don’t speak medical-ese.
Let’s break it down a bit. “Influenza-associated” means the result of the flu. “Medically attended” says that you sought medical care for the problem. “Acute respiratory illness” stands for a disease affecting your respiratory tract that is new and not something that has been going on for a while already.
Thus, the flu vaccine is estimated to have been 45% effective at preventing flu-associated respiratory illnesses that resulted in doctor’s visits. Not 45% effective in preventing the flu in general. Not flu in which you melt into your bed and don’t go anywhere for several days. But flu that got you to get you to the doctor’s office. The number was even higher for those 6 months to 17 years of age. Kids and adolescents had 55% for this type of vaccine effectiveness.
So, back to the original question: how is 45? In general, when the influenza virus strains in the vaccine match the strains that are circulating the population, such effectiveness tends to be between 40% and 60%. So 45% is kind of like sushi in a food court. Not the best that it could be. But it does it’s job.
Where did the CDC get these numbers? Well they came from the U.S. Influenza Vaccine Effectiveness Network, which conducted studies from October 23, 2019 to January 25, 2020. During that time period, five study locations in Michigan, Pennsylvania, Texas, Washington, and Wisconsin enrolled 4,112 patients, all 6 months of age and older, who had visited clinics for acute respiratory illness accompanied by cough when the flu virus was known to already be circulating in the area. The researchers asked each patient whether he or she had received the flu vaccine at least 14 days earlier this season and tested their noses or mouths for presence of the flu virus. Ultimately, 1,060 (26%) of the study participants ended up testing positive for the influenza virus. The percentage of participants in each site who had received the flu vaccine ranged from 38% to 61%.
From the results, they calculated an odds ratio. Not an odd ratio as in a weird ratio but an odds ratio calculated as such: the odds that a person who tested positive for the flu also had been vaccinated earlier in the season divided by the odds that a person who tested negative for the flu had been vaccinated. The following formula then calculated the estimated vaccine effectiveness: 100% x (1- odds ratio).
So this is a somewhat indirect method of evaluating the effectiveness of the flu vaccine. It is also from a specific sample of 4,112 patients. If you think political polls don’t really represent what people think, you can imagine that numbers from a sample of people from particular locations may not really represent what is occurring throughout the country. Plus, numbers for particular parts of the flu season may not end up holding throughout the entire flu season. This flu season is far from over. Oh, and remember this is vaccine effectiveness in preventing “influenza-associated medically attended acute respiratory illness.” Not the flu in general.
Moreover, don’t go around saying, “I’m 45. I’m 45.” That may not be your specific number. The flu vaccine probably offers different levels of protection to different people. A vaccine basically presents the viruses to your immune system and says, “hey watch out for these.” Therefore, the protection that you get depends on how your immune system reacts.
Regardless of your specific number, some protection is better than no protection. Nothing else even comes close to the vaccine in protecting against the flu. Taking supplements is not going to do it. Neither is a special diet, getting chiropractic treatments, douching your nose, or drinking whiskey. The CDC has estimated that the flu has already caused 12 to 17 million medical visits, 250,000 to 440,000 hospitalizations, and 14,000 to 36,000 deaths this season as of February 8, 2020. If you haven’t yet gotten the flu vaccine, it is still worth getting.