At the time of writing (2020-11-09 12:04 UTC) the article uses "90% of people" and "90% protection" interchangeably. I assume it means "90% of individuals achieve immunity", rather than "individuals achieve 90% immunity".
EDIT: See child comment re: Pfizer press release.
EDIT 2: See [1] for said press release, which has more detailed information than the BBC article.
EDIT: See child comment re: Pfizer press release.
EDIT 2: See [1] for said press release, which has more detailed information than the BBC article.
[1] https://investors.pfizer.com/investor-news/press-release-det...