Michael Osterholm, who directs the Center for Infectious Disease Research and Policy at the University of Minnesota, offered a scare story about flying while vaccinated during the pandemic on NBC’s Meet The Press,
[T]he doctor said this about traveling after being vaccinated. And it’s terrifying: “Let me just give an example on the airplane flight. When you get vaccinated, it’s like buying a fireproof suit that works 90 to 95 percent of the time. But it doesn’t work all the time. So why want to walk into a big fire if you don’t have to? So what they are basically saying is, ‘Yes, if you are vaccinated you can start opening up a lot of things in your life that you couldn’t do before.’ But now, if you know you’re going to be walking into a fire, why do it?”
But that’s not what the effectiveness data means. When we talk about a vaccine that is 95% effective against symptoms (90% effective against asymptomatic cases, i.e.. being a carrier) that is in comparison to someone that is not vaccinated. It tells us the reduction in risk that follows vaccination.
One common misunderstanding is that 95% efficacy means that in the Pfizer clinical trial, 5% of vaccinated people got COVID. But that’s not true; the actual percentage of vaccinated people in the Pfizer (and Moderna) trials who got COVID-19 was about a hundred times less than that: 0.04%.
What the 95% actually means is that vaccinated people had a 95% lower risk of getting COVID-19 compared with the control group participants, who weren’t vaccinated. In other words, vaccinated people in the Pfizer clinical trial were 20 times less likely than the control group to get COVID-19.
Saying a vaccine is 95% effective doesn’t ‘fail 5% of the time’. Someone that takes a 95% effective vaccine should have a 95% lower likelihood of catching the virus than someone who is not vaccinated. And someone who isn’t vaccinated doesn’t have a 100% risk of getting it, either, even when exposed.
Since early in the pandemic we’ve known that most people who become infected do not spread the virus. Instead we get a small percentage of people that are infected responsible for a large number of infections through superspreader events. Living at home with someone that has Covid-19 gives you less than a 50% chance of getting it yourself.
Even if that wasn’t true, and there was a Covid-19 positive person on a flight, not everyone on board is at equal risk due to variation in proximity and immune response.
Over the weekend CNN ran a piece making a similar error, that a 90% effective vaccine “translated into reality, that means for every million fully vaccinated people who fly, some 100,000 could still become infected.”
With an average of 1.4 million people per day passing through airport security over the past week, that would imply 140,000 Covid-19 infections per day just from air travel in an entire country with a 7-day average of just shy of 70,000 reported cases. Put another way, if there are twice as many infections as cases, then every infection in the country would relate to air travel.
Yet air travel is an indoor congregant setting, it’s a safer one than most indoor dining in your home town because of HEPA air filtration and downward air flow. It’s possible to get Covid-19 on a plane, but it’s rare.
CNN edited the piece, and this false claim about air travel has been removed, with the following correction,
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.
It’s easy to misunderstand what effectiveness data means for a vaccine. What the Pfizer and Moderna trials showed was that over a 3 month period, vaccinated people had a 0.04% chance of contracting Covid-19. You can extrapolate, then, to an extremely small chance on a given day.