What does 90 per cent 'effective' mean?
It sounds pretty good, hey?
But the vaccine
's 'efficacy' doesn't measure how well it stops the SARS-CoV-2 virus entering a vaccinated person's body.
Instead, it's a measure of stopping - or at least reducing the severity of - COVID-19.
And this vaccine, apparently, lowers your chances of getting sick by 90 per cent, compared to someone who hasn't been vaccinated.
Kylie Quinn, a vaccine expert at RMIT University, told ABC News: "If you had 10 people who you knew were going to be infected ... and you vaccinated those people before they were exposed, nine out of those 10 people would not develop (COVID-19)."
https://www.abc.net.au/radio/programs/coronacast/latest-segments/12025304
If you want to get technical (and who doesn't?!), vaccine efficacy and vaccine effectiveness are slightly different terms.
Vaccine efficacy is calculated through clinical trials, like the Pfizer/BioNTech trial. Vaccine effectiveness is measured out in the real world, once the vaccine has been approved for use in the general population.
To calculate the more-than-90-per-cent efficacy figure for BNT162b2, an external committee examined how many of the 94 infected individuals were vaccinated and how many received the placebo (a saline injection).
But the published results are a little light on detail. The announcement was made via press release - not a peer-reviewed journal paper - and it did not include the vaccine/placebo breakdown of infected participants.
The efficacy of the vaccine may change over time, too.
Dr Quinn says there's still a little way to go before the trial wraps up.
"This is the interim analysis of 94 patients. The study closes out at 164 individuals who have become symptomatic," Dr Quinn says.
"So we're not far enough."
