Moderna’s Chief Medical Officer Says That Vaccine Trial Results Only Show That They Prevent People From Getting Severely Sick, Not Necessarily That Recipients Won’t Still Be Able to Transmit
Okay, here’s the thing – I know this headline is going to get misinterpreted by approximately everyone who reads it, so let me be very clear about what Dr. Tal Zaks actually said.
Moderna’s Chief Medical Officer was speaking with Axios about the vaccine trial results. The data was phenomenal – 94.5% efficacy at preventing symptomatic COVID-19. That’s remarkable. That’s better than almost anyone was expecting just months earlier.
But Dr. Zaks wanted to make sure people understood exactly what the trials measured. And what they measured was whether vaccinated people got sick with symptoms.
What the trials did NOT measure – at least not directly – was whether vaccinated people could still carry the virus and pass it to others without ever developing symptoms themselves.
As Business Insider reported, Zaks told Axios that the public should not “over-interpret” the results to assume vaccinated people can immediately return to normal life without precautions.
“I think it’s important that we don’t change behavior solely on the basis of vaccination,” he said.
Now, look – Dr. Zaks told NPR that based on the science, it’s “likely” that the vaccine does prevent transmission. The preliminary data from the NIH trial was encouraging. But at that point in time, November 2020, they didn’t have solid proof yet.
This distinction matters enormously from a public health perspective. If vaccines only prevent symptomatic disease but not transmission, then vaccinated individuals could still be silent spreaders. That would change everything about how we think about reaching herd immunity.
The peer-reviewed NIH report noted: “Although mRNA-1273 is highly efficacious in preventing symptomatic COVID-19, there is not yet enough available data to draw conclusions as to whether the vaccine can impact SARS-CoV-2 transmission.”
The good news from the trial data: there were 11 cases of severe COVID in the study. All 11 were in the placebo group. Zero severe cases among the vaccinated. Science called it “absolutely remarkable”.
So when you see headlines about this, remember: Dr. Zaks wasn’t being pessimistic. He was being a scientist. And good scientists tell you exactly what they know and exactly what they don’t.
Stay safe out there. And have you had water today?
