HOME HOME   |   ABOUT   |   CONTACT US    |   EMAIL UPDATES   |   Español    

How Well Do Vaccines Work?

Vaccines work really well. Of course, no medicine is perfect but most childhood vaccines produce immunity about 90 - 100% of the time.

What about the argument made by some people that vaccines don’t work that well . . . that diseases would be going away on their own because of better hygiene or sanitation, even if there were no vaccines?

That simply isn’t true. Certainly, better hygiene and sanitation can help prevent the spread of disease, but the germs that cause disease will still be around. As long as germs still exist, they are they will continue to make people sick.

All vaccines must be licensed (approved) by the Food and Drug Administration (FDA) before being used in the United States. A vaccine must go through extensive testing to show that it works and that it is safe before the FDA will approve it. Among these tests are clinical trials, which compare groups of people who get a vaccine with groups of people who get a "control" (e.g, either a different vaccine or placebo).  A vaccine is approved only if FDA determines that it is safe and effective for its intended use. 

If you look at the history of any vaccine-preventable disease, you will virtually always see that the number of cases of disease starts to drop when a vaccine is licensed. Here’s a chart showing this pattern for measles:

Chart displaying cases of measles reported from 1950-2007. Strong dropoff of cases occurs around the time the vaccine was licensed.

Measles vaccine was licensed in 1962, and as you can see, that’s when the number of cases started to decline. (Measles didn’t completely disappear after 1993; there have just been too few cases to show up on this graph.)

If the drop in disease were due to hygiene and sanitation, you would expect all diseases to start going away at about the same time. But if you were to look at the graph for polio, for example, you would see the number of cases start to drop around 1955 – the year the first polio vaccine was licensed. If you look at the graph for Hib, the number drops around 1990, for pneumococcal disease around 2000 — corresponding to the introduction of vaccines for those diseases.

Vaccines are the most effective tool we have to prevent infectious diseases. Learn more about how vaccines work in the next section: Prevention.