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Doctor talks COVID-19 vaccine effectiveness, what happens after each dose

Ken Ramey
Posted at 4:29 AM, Feb 18, 2021

The mission of ABC15's Health Insider series is to dive deeper into the things impacting your health and the health of those around you. We're going in-depth with expert advice from people who know it, see it every day in their work and study it. Have a story idea? Contact the team at HealthInsider@abc15.com.

How quickly does your immunity develop once you get the COVID-19 vaccine?

Is it instant?

Do you really need both shots?

We've heard those questions time and time again during this pandemic, so we took them to Dr. Piyush Gupta with Blue Cross Blue Shield of Arizona.

After the first shot, do you have any immunity at all? Or is it that you don't have any immunity until after the second shot?

Dr. Gupta says the answer is yes, you'll have some immunity, but you won't have the maximum immunity until after both shots.

"After that first shot, I believe it's 70% effectiveness, so you're still protected about 70% of the time you encounter someone with COVID. It is still effective after the first shot, but it isn't completely effective as it is after the second shot where you achieve that 95%. That's why we're seeing cases of people getting that first shot and still seeing cases of COVID."

How long does it take for the vaccine to take full effect?

Dr. Gupta says it takes about two weeks, which is the same for the flu shot and other vaccines.

"It's not specific for the coronavirus vaccine. It's just how our immune system works. It takes about two weeks for the immune system to get energized and build up those antibodies that we need so that we are in full fighting mode again whatever vaccine were."

Dr. Gupta tells us that's another reason why we've seen some cases where people have gotten the first shot and still develop COVID.

If you think about it, if you develop 70% immunity two weeks after getting the first shot, there's still a 30% chance you could contract the virus. Two weeks after that second shot, your immunity goes up to roughly 95%, but it still takes time.