This week, the ratings of four Biotechnology stocks on Portfolio Grader are down. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

Keryx Biopharmaceuticals (NASDAQ:KERX) is on the decline this week, earning a D (“sell”) after receiving a C (“hold”) last week. Keryx Biopharmaceuticals focuses on developing and commercializing pharmaceuticals for the treatment of cancer and renal disease. In Portfolio Grader’s specific subcategories of Equity and Cash Flow, KERX also gets F’s. The stock price has fallen 8.5% over the past month, worse than the 1% increase the Nasdaq has seen over the same period of time. As of August 3, 14.4% of outstanding Keryx Biopharmaceuticals shares were held short. To get an in-depth look at KERX, get Portfolio Grader’s complete analysis of KERX stock.

This week, Acorda Therapeutics (NASDAQ:ACOR) drops from a C to a D rating. Acorda Therapeutics is a commercial stage biopharmaceutical company dedicated to the identification, development and commercialization of novel therapies that improve neurological function in people with multiple sclerosis (MS), spinal cord injury and other disorders of the central nervous system. The stock also rates an F in Earnings Momentum. Investors seem to agree with the downgrade and have pushed down the share price 13.2% over the past month. For a full analysis of ACOR stock, visit Portfolio Grader.

Sinovac Biotech (NASDAQ:SVA) earns a D this week, moving down from last week’s grade of C. Sinovac Biotech researches, develops, manufactures, and markets various vaccines, including flu vaccines and vaccines for Hepatitis A. The stock gets F’s in Earnings Revisions and Equity. For more information, get Portfolio Grader’s complete analysis of SVA stock.

This is a rough week for 3SBio (NASDAQ:SSRX). The company’s rating falls to D from the previous week’s C. 3SBio is a biotechnology company that engages in the research and development, manufacture, and distribution of pharmaceutical products in the People’s Republic of China. The stock price has fallen 15% over the past month. To get an in-depth look at SSRX, get Portfolio Grader’s complete analysis of SSRX stock.

Louis Navellier’s proprietary Portfolio Grader stock ranking system assesses roughly 5,000 companies every week based on a number of fundamental and quantitative measures. Stocks are given a letter grade based on their results — with A being “strong buy,” and F being “strong sell.” Explore the tool here.