This chart was created at twittercounter.com where you can find follower and tweet stats for any Twitter account. I compared stats for @pfizer_news with two other pharma-related Twitter accounts having a comparable number of followers (ie, @pharmaguy - me - and @swoodruff - Steve Woodruff).
Something unusual happened around Christmas last year - Pfizer somehow attracted about 3-4,000 NEW Twitter followers in just a few days! Did someone give Pfizer a Christmas present?
[Ha Ha! See comment about Pfizer PR people asking employees to follow. Maybe they sent employees a Christmas card?]
Perhaps Pfizer was spewing out a ton of informative Tweets that just naturally attracted 4,000 new followers. Oh, but wait, that can't be the reason. According to the stats, @pfizer_news has only posted 100 tweets since its launch last fall. It was practically silent around the end of the year in 2009.
More likely is that Pfizer got new followers by doing what it does best -- advertise! Kudos to them. What I want to know is how much did you pay per follower and where did you advertise?