VACCINE RESOURCE COMMITTEE
of the Edmonton Zone Medical Staff Association
View Full List of Vaccine Questions Here
General Vaccine Question #15:
How do we know vaccines are working?
Vaccines are not released to the public until they are proven to be effective. Vaccines such as influenza and
COVID-19 are modified based on circulating strains to ensure efficacy.
This graphic provides a comparison of case count for six vaccine-preventable diseases before and after introducing each vaccine in Canada. “Cases then” represents an average number of cases reported annually in Canada during the 5 years before routine vaccine use or closest possible 5 years where stable reporting was occurring. “Cases now” reflects the average number of cases reported annually in Canada from 2016 to 2020.
We know vaccines work based on at least three things:
How well they create an immune response.
How well they reduce disease in a community. Research on vaccines started in the late 1700s. For more than 300 years, scientists and researchers around the world have continued to study and monitor vaccines.
How well they prevent serious illness. Many vaccines are good at preventing someone from getting sick, but vaccines are not perfect. Sometimes, a vaccinated person will still get sick. Even if that happens, vaccines are excellent at preventing a child from more serious illness or death. Thanks in large part to childhood vaccination programs, the number of children who get sick, are hospitalized, or die from vaccine-preventable diseases has dropped dramatically over time.
Vaccines are so successful that some diseases are rarely seen anymore. Without vaccines, diseases that are rare can—and do—come back.
When measuring how well a vaccine works in a clinical trial it is called "efficacy". In Phase 3 clinical trials typically thousands of participants are given the vaccine and disease is measured in a group who receives the vaccine and a group who does not (or who receives a placebo) and they are compared. Sometimes antibody levels are measured in response to the vaccine instead of actual illness or disease (for example when a disease is rare). This study endpoint is called immunogenicity data instead of efficacy.
Vaccination prevents severe illness. People who were up to date on COVID-19 vaccinations were 10.5 times less likely than people who were not vaccinated to need hospital care for COVID-19 in early 2022.
Vaccines prevent deaths. Each year, vaccinations prevent 4 million deaths worldwide. Between 2021 and 2030, the measles vaccines alone will prevent an estimated 19 million deaths.
A disease is less likely to spread in communities where most people are vaccinated against the disease. Before a vaccine for measles came along in the 1960s, millions of people in the United States got the disease every year. By 2000, measles vaccination coverage was 95% or higher across the United States. Because so many people have received their measles vaccine, the disease was eliminated in the United States at that time; due to reduced measles vaccine uptake in recent years there has been resurgence of measles in communities with lower vaccine coverage in North America.
Some vaccines can eradicate diseases. Before a vaccine was used to eradicate smallpox, 3 out of 10 people with smallpox died. Global vaccination effort has resulted in elimination of naturally circulating smallpox.
Occasionally, people experience breakthrough infection even if vaccinated. This can happen because:
Few things work 100% of the time, including vaccines. Some vaccines have higher effectiveness than others. For most vaccines most people will be protected but some may still get sick. For instance, only about 3 in 100 fully vaccinated people will get measles if exposed. Even if a vaccinated person does become sick, often the illness is likely to be much less severe than if they had not been vaccinated.
Vaccines may not work as well in people with weakened immune systems. A weakened immune system cannot fight off diseases very well, perhaps due to advanced age, genetics, medications/treatments, or another illness or condition such as cancer. This is why it is so important that everyone around these people are vaccinated.
The person’s body was already fighting a serious illness at the time a vaccine is given. It is okay to vaccinate a child if they have a cold, but if they have a more serious illness, it is better to wait to ensure a more robust immune response to the vaccination. Keeping vaccine administration separate from acute febrile illness also helps to prevent misattribution of symptoms.
The person was infected with the virus or bacterium just before vaccination or soon afterward, then the vaccine might not have enough time to build immunity. It typically takes 2 weeks for immunity to develop after vaccination. Some vaccinations require multiple doses to achieve optimal immunity. This is why it is best to get vaccinated before someone is likely to be exposed to a disease.
The vaccine was a little different from the circulating strains of viruses. This can happen with the flu vaccine because the influenza virus changes a little bit every year. Even if a person gets influenza after being vaccinated, they are still less likely to have serious illness or need hospital care.
Sources
Government of Canada: Vaccines work: Case counts of 6 vaccine-preventable diseases before and after routine vaccination
United States Government: How do we know vaccines work?