San Francisco-based Vaxart has raised $20 million to back its work developing easy-to-take vaccine pills. The 9-year-old biotech revealed the raise in a Form D filed with the SEC. Just a few weeks ago Vaxart reported positive data from a Phase I study of its H1N1 flu vaccine in tablet form. A $12.5 million Series B financing led by Care Capital was closed back in 2010. Form D