Between 550,000 and 1.4 million people in West Africa could be infected with the Ebola virus by January 20, 2015, according to a report issued on Tuesday by the U.S. Centers for Disease Control and Prevention (CDC).

The top range of the estimate, 1.4 million, assumes that the number of cases officially cited so far, 5,864 according to the count kept by the World Health Organization, is significantly underreported, and that it is likely that 2.5 times as many cases, or nearly 20,000, have in fact occurred.

CDC emphasized that the projections, based on an epidemiological model that takes into account how many people each Ebola patient eventually infects as well as other factors, is based on data available in August. They therefore do not account for the recently announced U.S. government Ebola relief effort, which includes sending 3,000 members of the armed forces to the Ebola-stricken region.

"Extensive, immediate actions - such as those already started - can bring the epidemic to a tipping point to start a rapid decline in cases," CDC said in a statement.

(Reporting by Sharon Begley; Editing by Chizu Nomiyama)