Vaccine efficacy not same as effectiveness
For the majority of people who are not physicians or epidemiologists, the COVID-19 vaccine — among other things — has brought on new challenges in terminology.
Lesson 1: Efficacy and effectiveness are not the same thing.
“Efficacy is the degree to which a vaccine prevents disease — and this is key — under ideal and controlled conditions like in clinical trials when you’re comparing a vaccinated group to a placebo group. You have very defined and selected populations,’’ said Dr. Russell Faust, Oakland County Medical Director.
Effectiveness is how the vaccine protects in the real world.
“Now we’re talking hundreds of thousands or millions vaccinated, we’re talking anybody goes — except it’s 16 and up right now. We’re talking wide demographics, wide geographic areas, wide geographic areas with other endemic diseases, other endemic viruses, we’re talking about different countries, we’re talking about people taking different medications, who have different diseases and different ailments,’’ Faust said. “We’re talking about observational study now in the real world. This is effectiveness.’’
In most cases when people sign up for a vaccine they are unsure of whether it will be Pfizer, Moderna or Johnson & Johnson. Vaccine shopping is not recommended — most specialists agree that any of the three are good.
If you Google any of the three you will find different numbers for efficacy and effectiveness. Don’t let your head spin.
On Monday, the Centers for Disease Control and Prevention released some of the first real-world evidence that MRNA vaccines like Pfizer and Moderna are 90% effective at preventing COVID-19 infections, even asymptomatic cases.
The CDC study featured data from nearly 4,000 healthcare workers, first responders, and essential workers across six U.S. states. By getting both vaccine doses (and then allowing those shots two more weeks to take effect) they were about 90% less likely to catch COVID-19, despite their continued, consistent exposure to the coronavirus on the job.
“Let’s be really clear about this. Everybody wants 100% effectiveness. That’s what you want, that’s what I want. I want to get a vaccine where in the real world the success rate of it, the effectiveness is, 100% to guarantee I’m never going to get this disease,’’ Faust said.
That is not going to happen.
Even vaccines that have what would be considered low effectiveness in the real world prevent deaths of hundreds of thousands of people every year, according to Faust.
“The flu vaccine is only 40-50% effective in the real world, but it saves tens of thousands of lives in the U.S. alone, maybe hundreds of thousands,’’ Faust said. “Even with a 40% or 50% or 60% effectiveness in the real world, I would be delighted. If I get a 20-percent effective flu vaccine in a year I’m jumping for joy.’’
There are some years that the flu vaccine is not even 20% effective.
So while it may sound good that the COVID-19 vaccines reached 90% or 95% or 97% efficacy in trials, it is not the real world.
“What I really care about in public health is I care about the effectiveness of a vaccine of keeping people from being severely infected where they’re transmitting to others and being admitted to the hospitals and ending up in the ICU,’’ Faust said. “I care about that where we’re shutting down our hospitals — remember last March, April, May a year ago it was like warzone medicine. That’s what I care about. If a vaccine prevents that and I can keep people alive that’s what I care about the most.’’
The Pfizer and Moderna vaccines are over 90% effective against severe COVID-19 disease. Johnson & Johnson is over 85% effective in preventing severe COVID-19 disease, according to Faust.
That doesn’t mean Johnson & Johnson is a lesser vaccine. Pfizer and Moderna ran their clinical trials almost a year ago when there were no variants.
“When we’re comparing the published numbers we’re talking apples and oranges because of the different clinical trial times and honestly they’re different clinical trials. Not only different times but Johnson & Johnson went out of their way to run clinical trials in places where variants were known to be popping up,’’ Faust said. “I see that as very forward thinking, very progressive and frankly noble that they would stick their necks out like that and expose themselves to a potential failure — it’s totally possible those clinical trials would show horrible results because they knew the variant was everywhere and yet they did very well.’’
So basically the effectiveness of the three vaccines is about the same.
If one is 90% effective that means once a person is fully vaccinated that the chances of catching the virus are about 10%.
In other words, it’s much safer to be vaccinated, yet still there’s a chance of getting COVID. That’s why masks and social distancing remain important.
“No they’re not 100% safe. You can’t be fully vaccinated and go out and throw caution to the wind,’’ Faust said. “We’re in the 25th mile of a 26mile marathon. This is not the time to stop running. This is not the time to get crazy and get yourself exposed and get sick.’’
What’s needed to get back to normal is herd immunity. Faust prefers the term “community immunity” since, after all, we are not cows.
“We need to vaccinate as many people as possible, as rapidly possible. It’s not just the U.S., also as much of the global population vaccinated as possible,’’ he said.
“Understand even if we’re 100% vaccinated across the U.S. and the rest of the world is unvaccinated, every time someone gets infected with this virus it is mutating. During an active infection, variants are being produced. The risk is that as infections continue around the world the risk is there may be a variant that pops up that is frankly unaffected by your vaccine immunity or by your immunity if you’ve already had COVID-19,’’ Faust said.
“A variant may pop up that’s completely immune to your vaccines and then we start all over again — wildfire pandemic moving through our population. We need everybody vaccinated to put a stop to this pandemic,’’ he added.
And then he offered a reminder.
“We can also do it with masks, this is not rocket science. We can stop transmission person to person by wearing masks and distancing. Yes, I want to get everybody vaccinated so we can go back to a normal life but you know we can also put an end to this pandemic simply by wearing masks and distancing,’’ Faust said.