Richard Sprague

My personal website

How effective is the flu vaccine, really?

Created: 2020-02-21 ; Updated: 2020-02-28

Everyone agrees we should all get our flu shots. Everyone, from small non-profits and educational institutions to Big Greedy Corporations, Big Government agencies, and Faceless Bureaucracies – all agree that the flu shot is safe, necessary, and an all-around Good Idea for everyone.

So fine, sounds like we should all get our shots. But well does it actually work?

The CDC studies this. Each flu season they designate several hospitals throughout the country (including one in Seattle) to keep track of everyone who checks in with flu-like symptoms. The patients are then evaluated with a state-of-the-art test to see whether they indeed have the flu, and if so, which specific virus caused it. They also ask the person if they had a flu shot.

The interim results for February 2020 show:

of 4,112 children and adults with acute respiratory illness during October 23, 2019–January 25, 2020, the overall estimated effectiveness of seasonal influenza vaccine for preventing medically attended, laboratory-confirmed influenza virus infection was 45%.

45% is a little on the low side compared to other years, when it typically ranges from about 40-60%. Still, it’s not bad if you think of it as roughly 50-50. If I can halve my odds of getting the flu, it’s worth it, right?

But most people never get the flu. Some people get sick for other reasons, and some people get sick regardless of whether they had a shot or not.

Personal Scientists don’t care about the averages. Averages are meaningless if you’re not average. You care about you.

So I looked more closely at the CDC data.

Table 1: Absolute numbers of people
Vaccinated Not Vaccinated
Flu 390 670
Not Flu 1682 1370

Here’s the same data by percentage:

Table 2: People with flu-like symptoms (percentages)
Vaccinated Not Vaccinated
Flu 9 16
Not Flu 41 33

In other words, of the four thousand or so people studied so far this flu season, all of whom had flu-like symptoms, only about 9% had been vaccinated for this year’s strain. Another 16% had not been vaccinated. And the rest? The vast majority – three fourths – had something that wasn’t addressed by the vaccine. Ironically, almost half (41%) of all cases of flu-like symptoms were people who had been vaccinated.

The highly-respected Cochrane Review, in its 2018 study of flu vaccination’s affect on Influenza-like Illness (ILI), concluded:

71 people would need to be vaccinated to avoid one influenza case, and 29 would need to be vaccinated to avoid one case of ILI. Vaccination may have little or no appreciable effect on hospitalisations (low-certainty evidence) or number of working days lost.

There are many ways to read this year’s CDC data. If you’d like to believe the vaccine is worthwhile, then you’ll explain away the large number of vaccinated people at the hospital by pointing out that that maybe the type of person who gets vaccinated is also more likely to check in to the hospital when they have symptoms. You might also add that these numbers would have been even worse without the “herd immunity” that comes from widespread vaccination.

My own opinion is that yes, vaccination helps a little – but the effect is probably not even noticable in healthy people. About half of all the hospitalization cases are under age 18 or over 50, and my guess is that if you looked closer you’d see that each of the serious cases is somebody already at high risk due to some other condition. If you’re in reasonably good health overall, the vaccine won’t hurt, but it won’t help much either.

The flu vaccine isn’t nearly the obvious good that you’d think based on the highly-publicized advice you see everywhere. Yeah, maybe there’s some benefit to having people check in to the medical system for an annual flu vaccine (just getting your blood pressure and other vitals checked can help a lot of people). But on the other hand, all that publicity may actually hurt the cause of public health by (1) distracting people from far more important flu prevention tips like immunity-boosting proper diet and lifestle, and (2) raising the overall cost of healthcare by promoting public health measures that would not be justified if we had to pay for it ourselves.

Update: Texas A&M scientists conclude in Feb 2020 Clinical Infectious Diseases that quadrivalent and trivalent vaccines are equally protective, even against the B strains that supposedly the quadrivalent vaccines are optimised for.