What If the Vaccine Works Only Half the Time?

What If the Vaccine Works Only Half the Time?

  • A coronavirus vaccine doesn’t need to be perfect to still be valuable.

Dear Dr. Hamblin,

I heard an immunologist on the radio today say that a coronavirus vaccine could be only 50 percent effective, in which case we’d still have to “live” with the virus even after it arrives. With all the talk of the vaccine being the way out, this is terrifying. What if the vaccine isn’t totally effective? Will the virus really be with us forever?

Sydney Levitt

Toronto, Canada


No vaccine is perfectly effective. That isn’t bad news; it’s just a basic fact. No medicine is perfectly effective, no parachute is perfectly effective, and no person is perfectly effective at … whatever it is they do. But though vaccines are only partly effective at protecting a single person, they can still be extremely effective collectively.

Sydney Levitt

Toronto, Canada


No vaccine is perfectly effective. That isn’t bad news; it’s just a basic fact. No medicine is perfectly effective, no parachute is perfectly effective, and no person is perfectly effective at … whatever it is they do. But though vaccines are only partly effective at protecting a single person, they can still be extremely effective collectively.

Vaccine “effectiveness” takes into account lots of different factors: What percentage of vaccinated people develop antibodies? How many antibodies? How long do the antibodies last? How well do they protect the person from disease? Ultimately, you’re left with a rough average: what percentage of people who get vaccinated are protected for a meaningful amount of time.