We know that vaccines work.

But how well do they work?

Taken together, you have to say that vaccines work very well.

Remember, according to the CDC:

Vaccine efficacy/effectiveness (VE) is measured by calculating the risk of disease among vaccinated and unvaccinated persons and determining the percentage reduction in risk of disease among vaccinated persons relative to unvaccinated persons. The greater the percentage reduction of illness in the vaccinated group, the greater the vaccine efficacy/effectiveness.

They aren’t perfect though and some vaccines do work better than others.

For example, the MMR vaccine provides 99% protection (two doses) against measles, while the seasonal flu vaccine can vary from 10% to 60%, depending  on how well the flu vaccine matches the flu virus strains that are getting people sick that year.

Fortunately, most vaccines have over 90 to 95% effectiveness.

The exceptions, in addition to flu vaccines, are the mumps and pertussis vaccines.

In addition to problems with waning immunity, they have lower rates of effectiveness than most other vaccines:

• mumps – 78% effectiveness
• acellular pertussis vaccine – 75 to 80% effectiveness

That’s probably why we are seeing more outbreaks of mumps and pertussis among vaccinated children and young adults, although intentionally unvaccinated children and adults are also contributing to most of those outbreaks.

For More Information On Efficacy Rates of Vaccines:

• CDC – Principles of Epidemiology
• Childhood vaccine effectiveness – easy to use table
• PinkBook – Measles
• PinkBook – Mumps
• PinkBook – Pertussis
• CDC – Vaccine Effectiveness – How Well Does the Flu Vaccine Work?
• Vaccines are Effective
• Vaccine Epidemiology: Efficacy, Effectiveness, and the Translational Research Roadmap

• Vaccines