COVID-19: Quebec hopes to begin vaccinating youngsters by year’s end, health minister says The new study by the Institut national de santé publique du Québec says the “efficacy against infections increases when the interval between doses is greater than that recommended by the manufacturers.”For example, the study revealed that the Oxford-AstraZeneca vaccine was 47 per cent effective at preventing infections when the second dose was given three to four weeks after the first, as recommended by the manufacturer.
But that efficacy jumped to 92 per cent when the second dose was administered at least 16 weeks after the first.The study also found that three vaccines — Pfizer-BioNTech, Moderna and AstraZeneca — have been highly effective at.