The Canadian COVID-19 Emergency Department Rapid Response Network (CCEDRRN) has harmonized data collection for COVID-19 tested patients across 50 emergency departments in 8 provinces, including BC. This project used CCEDRRN’s registry infrastructure to determine the real-world effectiveness of vaccines in reducing severe COVID-19, as opposed to estimates from clinical trials, which often do not include patients with other medical conditions, or from marginalized populations.
The study took place from July to December 2021, during which time the Delta wave of COVID-19 was occurring; and only people with two vaccine doses (the recommended number at that time) were included. A total of 2,432 patients were included from eight hospitals across four provinces.
The study found that mRNA vaccines were 91% effective at preventing symptomatic infection requiring emergency department evaluation and 91% effective at preventing hospitalization. This means the odds for individuals in developing symptomatic COVID-19 infection requiring emergency department evaluation is approximately one tenth in individuals who are vaccinated against SARS-CoV-2, compared to those who are unvaccinated. This is comparable to the BCCDC’s estimate of 95% effectiveness against hospitalization.
This project demonstrated that emergency department networks can be a useful tool for monitoring population health, and could be used for other situations, such as monitoring flu vaccine effectiveness, or complications arising from climate events, such as heat waves.