Even one vaccine dose could prevent 8 out of 10 COVID-19 cases: BCCDC

People who receive even just their first dose of the COVID-19 vaccine substantially reduce their risk of becoming infected by the virus, the BC Centre for Disease Control (BCCDC) said on Friday.

In a release, the BCCDC said early vaccine effectiveness results in the province show the first dose of the COVID-19 vaccine reduced the risk of contracting the virus in long-term care residents and health care workers by 80% percent within two to three weeks of receiving the vaccine.

“These findings… are very promising and reinforce the substantial benefit provided by the first dose of the mRNA COVID-19 vaccine in these priority populations,” said Dr. Danuta Skowronski, lead for the Influenza and Emerging Respiratory Pathogens Team at the BCCDC. “They also help to answer one of the important unanswered questions after the clinical trials about the effectiveness of the vaccines in the elderly and notably those within long-term care.”

The analysis, led by Dr. Skowronski, looked at COVID-19 cases that occurred among vaccinated long-term care residents and health care workers between late December 2020 and early February 2021, the BCCDC said.

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Researchers observed a pronounced drop in the number of cases among vaccinated individuals in both groups, beginning about 14 days after vaccination. This included a reduction in hospitalizations and deaths among vaccinated long-term care residents.

Vaccines begin to work “a couple of weeks” after vaccination, the BCCDC said. Researchers compared the risk of becoming a COVID-19 case in the first ten days following vaccination before the vaccine would have had an effect, to the risk two weeks or more after vaccination. Doing this, they were able to show vaccine effectiveness of 80% or more within a few weeks. This means that a single dose of vaccine could prevent at least eight out of every 10 cases of COVID-19.

The results are based on surveillance observations and have not yet been published in a peer-reviewed paper but are being shared in the context of a public health emergency.

They are comparable to vaccine effectiveness results released by Quebec. Together, the studies “reinforce the substantial protection for these important populations afforded by a single dose of COVID-19 vaccine,” the BCCDC said.