FACTBOX-Africa the worst hit by AIDS, by far

Oct 20 (Reuters) - AIDS vaccine researchers meeting in Paris this week said they are trying to figure out how and why a vaccine tested in Thailand appeared to have prevented about 31 percent of expected HIV infections.

All agree a vaccine would be the best way to fight the pandemic, but none formulated yet has shown clear or robust effects.

Here are some facts about AIDS.

* Sub-Saharan Africa remains the region most heavily affected by HIV, accounting for two thirds of all infections and 75 percent of AIDS deaths in 2007.

* Global deaths from AIDS reached an estimated 2 million in 2007, down from 2.1 million deaths in 2006. Since the AIDS pandemic started in the early 1980s, more than 25 million people have died from the virus.

* The annual number of new HIV infections declined to 2.7 million in 2007 from 3.0 million in 2001.

* Some 33 million people had human immunodeficiency virus infections in 2007, most of them in Africa, according to the 2008 United Nations report on the AIDS epidemic.

* In virtually all regions outside sub-Saharan Africa, HIV disproportionately affects people who inject drugs, men who have sex with men, and sex workers.

* An estimated 1.9 million people were newly infected with HIV in sub-Saharan Africa in 2007, bringing to 22 million the number of Africans living with HIV.

* More than half of the 9.5 million people who need AIDS drugs cannot get them, a United Nations report said at the end of last month.

(Writing by David Cutler, London Editorial Reference Unit, editing by Maggie Fox and Sandra Maler)