Because of the demonstrated efficacy of immediate vaccination, all recipients will now be immunized immediately.[19][20] Ring vaccination is the method used in the program to eradicate smallpox in the 1970s. The trial will continue to assess whether the vaccine is effective in creating herd immunity to Ebola virus infection.[21] In December 2016, a study found the VSV-EBOV vaccine to be 95–100% effective against the Ebola virus, making it the first proven vaccine against the disease.[22][23][24]