CNN Doesn’t Understand Vaccines — or Math

CNN currently is running an explanatory piece titled, “How to fly safely a year into the pandemic.” Unfortunately, whoever was responsible for the article does not understand vaccines — or basic math.

One paragraph of the article reads:

In addition, real world studies of the Pfizer-BioNTech and Moderna vaccines show they are only 90% protective against the coronavirus, not 95% as reported in clinical trials. Translated into reality, that means for every million fully vaccinated people who fly, some 100,000 could still become infected.

Translated into actual reality, a 90 percent effective vaccine refers to the reduction in odds of a vaccinated person being infected relative to somebody who has not taken the vaccine. That is, in a given group of, say, 2,000 people, if 100 unvaccinated people would ordinarily get COVID-19,  just 10 vaccinated people in the same sized group would get the virus. It doesn’t mean that 200 vaccinated people would get the virus!

For the CNN statistic to be true, it would mean that without a vaccine, everybody who flies on an airplane is guaranteed to get infected — that is, all million passengers in the scenario above would get COVID-19. This is nowhere near the truth based on months of data from people flying before vaccines were even released.

It’s also worth noting that the vaccines not only prevent infection, but substantially reduce the odds of severe infection among the small number of vaccinated people who get infected. And the percentage of vaccinated people facing hospitalization or death is near zero.

What’s amazing is not only that this story was written by somebody tasked with explaining travel safety to readers, or that that it got past an editor. What’s especially incredible is that the story was published on Friday, and thus has been up for two days without correction.

That said, perhaps we shouldn’t be surprised. For months, public health officials have been downplaying the effectiveness of the vaccine, sending the message that getting vaccinated should not change people’s behavior. This is likely one reason why a recent poll found that just 29 percent of vaccinated adults believe it is safe to travel.

In case CNN does finally get around to fixing the story by the time you read this, here it is saved for posterity:

UPDATE: Since publishing this story, CNN has issued a correction stating, “A previous version of this article incorrectly extrapolated vaccine efficacy and the probability of becoming infected with Covid-19 aboard airplanes. The risk is much lower than stated in the original version.”

“Much lower” is one way of putting it.