Vaccine math. Results vary because …

According to the AstraZeneca Media Release, 22 March 2021, “The AstraZeneca US Phase III trial of AZD1222 demonstrated statistically significant vaccine efficacy of 79% … based on 32,449 participants accruing 141 symptomatic cases of COVID-19. The trial had a 2:1 randomisation of vaccine to placebo.”

“A careful review of all available safety data of more than 17 million people vaccinated in the European Union (EU) and UK with COVID-19 Vaccine AstraZeneca has shown no evidence of an increased risk …”

Update:

The Washington Post, 25 MAR 2021

An updated company analysis of the coronavirus vaccine developed by AstraZeneca and the University of Oxford showed that the two-shot regimen was robustly effective — 76 percent at preventing symptomatic illness — according to a news release from the drugmaker late Wednesday.

Among people 65 and older, the vaccine was 85 percent effective, the company reported.

New York Times, 9 APR 2021

UK plus & 30 EU countries have administered 34 million AstraVeneca doses and report a blood clot condition in 222 patients and 18 fatalities. 

Risk Factor for blood clots = 1: 153,000 

Risk of death ~ 1: 2,000,000

Many countries including Australia advise the use of the AstraZeneca vaccine for the 50+ age group as the blood clot condition appears mostly in younger patients.