Questions remain even as highly promising COVID-19 vaccines are on the cusp of release

After months without a visible breakthrough, everything sped up in November, when several pharmaceutical companies made encouraging preliminary announcements about the efficacy of their vaccines. Researching, testing, approving, manufacturing and distributing a new vaccine usually takes a decade or longer.

The breakneck pace of development, resulting in half-a-dozen Covid-19 vaccines, saw an unprecedented blitzkrieg of public and private research backed by huge sums of money and provisional orders for billions of doses. But all parties involved insist that corners have not been cut.

"Initial supply of COVID-19 vaccines will be limited, so healthworkers, older people and other at-risk populations will be prioritised," World Health Organization (WHO) head Tedros Adhanom Ghebreyesus recently tweeted. The world's poorest countries, he warned, should not have to wait until wealthy ones that have reserved billions of doses are served.

Basically, the efficacy of a vaccine is determined by comparing the number of people who get sick with Covid-19 in a group of vaccinated volunteers compared to another group that receives a placebo instead of the active drug. The threshold for releasing the findings -- the number of people infected with Covid-19 -- was different in each case: 170 for Pfizer/BioNTech, 95 for Moderna, 131 for AstraZeneca/Oxford, and only 39 for the Gamaleya Institute.