An official website of the United States government
The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before
sharing sensitive information, make sure you’re on a federal
government site.
The site is secure.
The https:// ensures that you are connecting to the
official website and that any information you provide is encrypted
and transmitted securely.
Cluver C, Novikova N, Koopmans CM, West HM.Cluver C, et al. Among authors: novikova n.Cochrane Database Syst Rev. 2017 Jan 15;1(1):CD009273. doi: 10.1002/14651858.CD009273.pub2.Cochrane Database Syst Rev. 2017.PMID: 28106904Free PMC article.Review.