What is vaccine efficacy

Some information may be out of date. Visit our coronavirus hub and follow our live updates page for the most recent information on the COVID pandemic. All new vaccines undergo clinical trials to test how well they work. The developers of a vaccine candidate usually determine the main goals of their trial in their clinical trial study protocol. These goals are called the primary endpoints. Scientists can calculate how well a vaccine candidate works by looking at the difference in new cases of the disease between the group receiving a placebo and the group receiving the experimental vaccine.

This is called vaccine efficacy. Stay informed with live updates on the current COVID outbreak and visit our coronavirus hub for more advice on prevention and treatment.

Volunteers taking part in vaccine clinical trials often undergo close monitoring. Many clinical trials have exclusion criteria such as pregnancy, particular health conditions, and age. Trials involving experimental vaccines rarely include children or seniors until scientists have collected a significant amount of safety data to protect these groups from potential harm. Vaccine efficacy only provides information about how well a vaccine works under the conditions of the clinical trial.

With efficacy, you need to realize that clinical trials are based on a small number of people relative to the general population. We know that when you get into millions of people, the results will vary. A clinical trial gives some participants the vaccine and others a placebo. For example, case-control studies assess effectiveness by comparing the vaccination status of individuals who develop the disease cases with a group of individuals without the disease controls who are also representative of the population from which the cases arise.

If the vaccine is effective, the cases are more likely to be the unvaccinated individuals. Two-strike Ebola vaccine enters human trials. Home Vaccineswork What is the difference between efficacy and effectiveness?

For some diseases, if enough people are immune then transmission of the disease is reduced or eliminated. This is particularly so for diseases such as rubella and pneumococcal disease. High vaccine coverage must be maintained in order to prevent the disease re-entering the population. Also, some people are unable to be vaccinated due to certain conditions such as immune suppression. Maintaining immunity in those around these people protects them from disease.

Estimated duration of protection from vaccine after receipt of all recommended doses 1,2. Community protection is important to stop transmission to those too young to be immunised, or those who cannot have the MMR vaccine. Duration of immunity varies in different populations. It is not as long-lived as measles or rubella.

To date antibody concentrations have remained high in vaccinees. Community protection means vaccinating children reduces the disease in all ages in the community.