Buffett-led Berkshire Hathaway opened a position in Pfizer in the third quarter of 2020. In a regulatory filing last week, though, Berkshire revealed that it had dumped all of its shares in the big drugmaker.. Pfizer won emergency use authorization (EUA) for COVID-19 vaccine Comirnaty (BNT162b2) in the U.S. and in Europe. It lined up major supply deals for Comirnaty totaling in the hundreds of millions of doses. The company also reported good news for several of its pipeline programs. All we can do is guess why Berkshire sold all of its Pfizer shares…