U.K., Israel studies show single dose effective

Studies from Israel and the United Kingdom showed that a single dose of the Pfizer-BioNTech vaccine significantly reduced COVID-19 infections, helping to guide British Columbia's decision to delay the second dose of vaccines by four months.

B.C. provincial health officer Dr. Bonnie Henry has said the plan is based on research in the two countries as well as evidence collected by the BC Centre for Disease Control and in Quebec.

A study published by the University of Cambridge in the U.K., which has not yet been peer-reviewed, suggests that a single dose of the Pfizer-BioNTech vaccine can reduce the number of asymptomatic COVID-19 infections by 75 per cent.

In Israel, researchers studied the effects of a single dose of the same vaccine and published their findings in The Lancet medical journal, concluding that it was 85 per cent effective against symptomatic COVID-19 infections.

Also in The Lancet, a U.K. study found that the Oxford-AstraZeneca vaccine is 81 per cent effective when its second dose is given three months after the first, compared with 55 per cent efficacy after six weeks.

Horacio Bach, an adjunct professor of infectious diseases at the University of British Columbia, says the province has enough evidence to back the four-month interval, though he believes it is the first in the world to delay the second dose for that long.