Mixed vaccines provides strong protections against COVID-19 and Delta variant: BCCDC

British Columbians who received an AstraZeneca vaccine for their first dose then followed up with an mRNA shot can rest assured that they’re protected.

The British Columbia Centre for Disease Control has released findings from a study that shows having a mixed combination of an AstraZeneca vaccine and an mRNA shot provided recipients with 91 per cent protection from infection of both COVID-19 and the Delta variant, and reduced the risk of hospitalization for those people by 99 per cent.

According to the study, the mixed combination provided protection levels very similar those associated with having received a double dose of an mRNA vaccine.

People in the study who had a double dose of the Pfizer vaccines had 91 per cent protection to all infections and 92 per cent protection against Delta, and a 98 per cent reduced risk of hospitalization from all infections, including Delta. Comparatively, those who received the Moderna shots had 92 per cent protection against COVID-19 and 93 per cent protection against the Delta variant, and again a 98 per cent reduced risk of hospitalizations.

Those figures far surpass the 72 per cent protection against COVID-19 and 70 per cent protection against Delta and the 93 per cent reduced hospitalization risk that were associated with just having received the AstraZeneca shots.

The study noted that, four months after having received their second doses, the participants still had an infection protection level above 80 per cent, and hospitalization risks were still reduced by over 90 per cent.

The findings also noted that protection levels are higher when the interval between doses is more than six weeks. The study shows that protection levels for those who received the two doses of the Pfizer vaccine within three or four weeks was around 82 per cent, the five to six week interval was around 85 per cent protection, the seven to eight and nine to 11 week intervals had protection rates of 92 per cent, dropping to 90 per cent for those who waited 12 to 15 weeks, but climbing to 93 per cent when the intervals are 16 weeks or higher.

Doctor Bonnie Henry noted Tuesday that this data was taken into consideration by the B.C. government prior to announcing the plan to roll out COVID-19 boosters for all British Columbians who want one, with the shots only being made available six months after having received their second dose.

These findings come from a study of 246,656 British Columbians between May 30 and Sept. 11, 2021 during the rise of the Delta variant in B.C. During the study they recorded 17,077 cases.

The BCCDC notes that 67 per cent of the participants in the study had received two doses of the Pfizer shot, 16 had received Moderna vaccines, eight per cent had a mix of mRNA vaccines, five per cent had received an AstraZeneca dose and a dose of an mRNA vaccine, and three per cent had just received the AstraZeneca doses.

The study was comprised of people aged 18 and older, but did not include long-term care residents. The research was conducted on a test-negative design.