Banc of America Securities-Merrill Lynch reinstated coverage of Gilead Sciences Inc with a buy rating, saying upside to consensus estimates over the next few years is likely, driven by strength in the drugmaker's HIV medicines amid few competitive threats.

Gilead has diversified its portfolio over the years, but HIV products are 80 percent of revenues, and we forecast HIV will dominate for the foreseeable future, analyst Rachel McMinn wrote in a note to clients.

The analyst set a price objective of $54 on Gilead's stock.

McMinn reinstated coverage of Biogen Idec Inc with an underperform rating, saying the company's multiple sclerosis drug Tysabri is extremely vulnerable from competitors' drugs that are in late-stage development.

While the most efficacious products to date do not have pristine safety profiles, feedback from our consultants is that the known side effects with competitors are far superior to the debilitating neurologic side effect observed with Tysabri, analyst McMinn said.

The analyst, who set a price objective of $45 on Biogen stock, said six multiple sclerosis products are in late-stage development.

BofA-Merrill also reinstated coverage of Celgene Corp and Amgen Inc with a neutral rating. It has a price objective of $58 on Celgene and $63 on Amgen.