Volume 8 • 2021 • Issue 4

Ask a Clinical Pharmacy Specialist: How Effective are COVID Vaccines? Dr. Mark Donaldson Associate Principal, Vizient Inc. In June, when about 25 million Canadians had received at least a first dose of a COVID-19 vaccine, Dr. Mark Donaldson gave a presentation to CDA about vaccine effectiveness, the durability of immunity, and COVID variants. Vaccine effectiveness in the population In a large population of vaccinated people, mRNA vaccines (e.g., Moderna and Pfizer-BioNTech) had 95% effectiveness while ChAdOx1-S recombinant vaccines (e.g., AstraZeneca) had 76%. “In people who already had moderate to severe COVID, the vaccines, including AstraZeneca, where nearly 100% effective,” says Dr. Donaldson. In the US, the Centers for Disease Control and Prevention (CDC) track breakthrough infections in vaccinated people. “Among these breakthrough cases, there hasn’t been a single reported case of a vaccinated person who has become infected with COVID transmitting the virus to someone else,” he says. Out of >95 million Americans who are fully vaccinated against COVID-19: • 0.007% of breakthroughs were symptomatic • 0.0006% required hospitalizations for COVID-19 • 0.0001% resulted in death from COVID-19 Durability of immunity Pfizer-BioNTech did a clinical trial of 46,000 international participants to determine efficacy 6months after vaccination, which included a control group of unvaccinated people. Among the control group, 850 people got COVID-19, with 32 cases defined as severe. Among the vaccinated group, 77 people got COVID-19, but none of the cases were severe. “About 800 participants were in South Africa,” says Dr. Donaldson, “where among the control group, some people had the Beta variant, but none of the vaccinated people got it, which suggests that the vaccine is effective against the variant.” The trial found that the vaccine had a 92% efficacy rate after 6 months. In a study of real-world effectiveness, 4,000 health care workers and essential workers in the US collected nasal swabs to be tested for COVID each week between mid- December and mid-March. Among these people, 63% were fully vaccinated (two doses of the vaccines) and 12% had 34 | 2021 | Issue 4