What happened

Shares of the biotech heavyweight Amgen (NASDAQ:AMGN) gained an astounding 20.9% during the month of April, according to data from S&P Global Market Intelligence. Amgen's stock took flight in April for two underlying reasons. 

So what

First, Amgen's double-digit April rally initially got underway when the company announced a collaboration with Adaptive Biotechnologies (NASDAQ:ADPT) to develop an antibody against the COVID-19 respiratory illness. For reasons that aren't altogether clear, every biotech company associated with a COVID-19 treatment or vaccine has been racing higher of late. Amgen, for its part, proved to be no exception to this general trend.  

Close up view of the novel coronavirus.

Image source: Getty Images.

Second, Amgen, along with a host of other blue chip healthcare stocks, appeared to perk up last month in response to the harsh economic realities of this pandemic. While healthcare stocks aren't entirely immune to the economic impacts of COVID-19, many of these companies are still generating profits during this turbulent period. The same can't be said for most airlines, sit-down restaurants, or oil and gas companies right now. Amgen, in fact, recently reported fairly strong first-quarter sales across the bulk of its product portfolio. 

Now what

Is Amgen's stock still a screaming buy? Prior to this sizable upswing in April, Amgen was easily one of the most attractive value plays in the large-cap biotech space. At this point, however, Amgen's shares are arguably fairly valued at best. The company's shares, after all, are now trading at a hefty 5.3 times 2021 projected sales. That's not exactly bargain territory for a large-cap biotech stock. Therefore, investors may want to wait before buying shares.