Will the vaccine work as well in the real world (compared to clinical trials)?

Good news! Research is already showing that the vaccine is working really well in the real world. Here’s how doctors try to figure out how a vaccine works in real life conditions.

Efficacy versus Effectiveness

Randomized clinical trials are considered the gold standard in medical research. We say they measure the “efficacy” of a new drug or vaccine. Efficacy is sometimes described as how well something works under ideal circumstances. Once a new drug or treatment is proven to work in tightly controlled clinical settings, people start using it in the real world. How well something works in the real world is usually called “effectiveness”.

What factors affect real-world effectiveness?

There are three things that generally impact how well a vaccine works in the real world:

  1. Population characteristics: Different people can respond differently to vaccines. For example, older people might have a weaker immune response. Or people with different health conditions or poor nutrition might have a weaker immune response. That’s why we want the people participating in clinical trials to be similar to the people who get the vaccine in the real world. 
  2. The virus changes: Viruses change over time; it’s a normal process. But changes to the virus produce new variants of the virus (sometimes called strains or mutations). If the vaccines are tested during a time when one variant is common, but deployed in the real world when another variant is common, the real-world effectiveness can be different than what we saw in the clinical trials.
  3. Program implementation factors: During clinical trials, doctors are very careful to store the vaccine at exactly the right temperature, administer precisely the right dose, and work hard to make sure participants get their second dose right on time. In the real world, things go wrong. People might get the doses late or early. Or the freezer might not be the exact right temperature. 

How will we know if it’s working in the United States?

The CDC is working with dozens of states and health care providers to measure exactly how well the vaccine is working in the real world. Aside from the official data, many of us will start to see how well the vaccine is working in our own homes and neighborhoods.

Last update: February 25, 2021 8:16 pm ET

Science review: JAB, SKB