Vaccines work and they work very well.
Unfortunately, they don’t work 100% of the time.
Vaccines and Breakthrough Infections
A breakthrough infection is the term for when you get sick despite having been vaccinated and responding to the vaccine.

On the plus side, breakthrough infections are typically much milder than what you would have gotten if you were unvaccinated.
For example, compared to chicken pox in an unvaccinated child, breakthrough chicken pox:
- causes fewer chicken pox lesions (less than 50 lesions vs 200 to 500 lesions)
- goes away faster (4 to 6 days vs at least 7 days)
- has less or no fever
- is less contagious
And that’s just another good reason and benefit to getting vaccinated.
More on Vaccines and Breakthrough Infections
- Are the Risks Greater Than the Benefits for Any Vaccines?
- The Benefits and Risks of Delaying Vaccines
- What Are the Pro and Con Arguments for Vaccines?
- Ask the Experts: Chickenpox (varicella)
- ACIP – Prevention of Varicella
- Why do we continue to use vaccines that are not 100% effective?
- Vaccine Effectiveness – How Well Does the Flu Vaccine Work?
- Another Benefit of Vaccines: Milder Disease
- Fatality Rates Of Small-Pox In The Vaccinated And Unvaccinated
- Vaccine adverse events are rare – vast benefits outweigh small risks
- The benefits of the measles vaccine go beyond just protecting against measles, 2019 edition