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Measuring Vaccination Impact & Coverage

British Columbia is closely monitoring vaccine safety, uptake and effectiveness.

Last Updated: October 14, 2021

Vaccine effectiveness

Vaccine efficacy and vaccine effectiveness are both measures of protection against a disease. They tell us how less likely a vaccinated person is to get a particular disease compared to a non-vaccinated person. 

Vaccine efficacy is calculated using data from vaccine clinical trials. 

Vaccine effectiveness is calculated using real-world experience and data once a vaccine is approved and in use. It takes into account more real-world complexities and is more representative of all people and a diversity of situations and challenges. 

We often hear the different COVID-19 vaccine efficacies being compared to one another, but this is not always a meaningful comparison and we need to be very cautious when we try to compare them. COVID-19 vaccine efficacies were determined through different vaccine clinical trials, but these clinical trials were not done under the same circumstances or at the same time. Factors that can impact clinical trial results include:

  • Variants: There are several prominent COVID-19 variants across the globe. A few of these variants have been shown to be more infectious than the original strain of COVID-19. Some COVID-19 vaccine trials were done at times and in places where there weren’t many (or any) variants, whereas other trials were done when there were large numbers of COVID-19 making it easier to catch COVID-19.
  • Timing: Primary COVID-19 vaccine clinical trials were done at different times throughout 2020. During some clinical trials, it may have been easier to get COVID-19 because transmission rates were higher at that time, or the trials may have studied different virus variants that were circulating in different parts of the world.
  • Location:  COVID-19 vaccine clinical trials were done in different countries. Some countries have experienced far more cases of COVID-19 than others, meaning transmission rates were higher in certain places during clinical trials.
Effectiveness tells the story of how vaccines are performing in the real world outside of trials. All vaccines approved in Canada and available in BC are safe and effective and will help protect you against COVID-19. While some people may still get COVID-19 after they have been vaccinated, all vaccines have been shown to have a high level of protection against serious COVID-19 illness and death. 
As we monitor the impact of the vaccines in our communities and province, we can start to see the impact a couple of weeks after vaccination. The first people to be vaccinated in B.C. were long term care and assisted living residents and health care workers. Within two to three weeks of receiving their first dose of vaccine, there was a pronounced drop in the number of cases among vaccinated individuals, a reduction in the number of outbreaks in these facilities, and a reduction in hospitalizations and deaths among vaccinated long term care residents.
In clinical trials, those who had received a COVID-19 vaccine were significantly less likely to become sick with COVID-19, to end up in hospital, or to die from COVID-19. 

COVID-19 is a relatively new disease and B.C. continues to monitor vaccine effectiveness. We are still learning how our immune system responds to infection and immunization and how long immunity lasts after getting vaccinated.

B.C. vaccine effectiveness results: Two doses 

Research from the BC Centre for Disease Control (BCCDC) show that two doses of COVID-19 vaccines are providing strong protection against COVID-19. This protection has been maintained for at least four months.  

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Vaccine effectiveness findings include:

  • Two doses prevent about 95% of COVID-19 hospitalizations. Preventing serious outcomes is the main goal of the vaccine program.
  • Two doses of either mRNA vaccine was more than 90% at preventing COVID-19 infection. Two doses of the AstraZeneca vaccine were more than 70% effective against infection. People who got one AstraZeneca dose followed by one mRNA vaccine dose (so-called “mix and match”) had protection that was as good as with two mRNA doses.
  • The vaccines are working similarly well in protecting against infections and hospitalizations due to the Delta variant, despite being more transmissible than other variants.
  • Vaccine protection was stronger when people received their second dose more than six weeks after their first dose.
  • No signs of waning: Vaccines are providing strong protection of more than 80 to 90 per cent has been maintained at least four months after the second dose.

Learn more about the vaccine effectiveness findings.

B.C. vaccine effectiveness results: One dose
  • A single dose of all vaccines available in B.C. (mRNA or AstraZeneca/COVISHIELD) protected well against hospitalization, reducing the risk by more than 80%. Learn about the results.

  • A single dose of a COVID-19 mRNA vaccine reduced the risk of getting COVID-19 by two-thirds in adults 70 years of age and older during the peak of the spring 2021 wave in B.C. when Alpha (B.1.1.7) and Gamma (P.1) variants made up 70% of circulating strains. Read the paper.

  • Risk reduced by 80% in long-term care residents and health care workers, the first people to be vaccinated in B.C. There was also a reduction in hospitalizations and deaths among vaccinated long-term care residents. Learn about the results.

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B.C. vaccination data  

B.C. Surveillance Dashboard provides:

  • Vaccination coverage for your health authority, community and by age. COVID-19 vaccination coverage is the percentage of people who have received one or more doses of COVID-19 vaccine in relation to the overall population.
  • Information about cases and hospitalizations by vaccination status.

Find the number of COVID-19 vaccine first and second doses administered in B.C. on the British Columbia COVID-19 Dashboard. Refer to the “Vaccine Information” tab on the bottom to see the number of doses administered (i.e. injected) and the number of doses distributed  (i.e. shipped to BC).


SOURCE: Measuring Vaccination Impact & Coverage ( )
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