WHO spokesman Gregory Hartl said the production will be "substantially less" than the goal of 94 million doses a week, because some manufacturers are still working on vaccines for seasonal flu.
The original estimate was based on a plan for drugmakers to switch all production capacity from season flu to H1N1 and using an additive adjuvant to stretch those supplies. No new estimate of production has been given by the WHO.
Despite concerns that multiple doses would be necessary for each person, recent research has shown one dose of the vaccine should provide adequate protection, the organization said, alleviating some of the supply demands.
"All the clinical trial results that we have seen show that apparently one dose is enough," Hartl said.
However, even with that news WHO director general Margaret Chan said in a statement, "Current supplies of pandemic vaccine are inadequate for a world population in which virtually everyone is susceptible to infection by a new and readily contagious virus."
The WHO also announced Friday that deaths from the H1N1 influenza virus have reached 3,486.
Amid growing fears that poorer nations will be unable to procure and provide vaccine to their citizens, the United States led nine countries which on Thursday pledged to make 10 percent of their swine flu vaccine supply available to other nations in need.
Australia, Brazil, The United Kingdom, France, Italy, New Zealand, Norway and Switzerland are also participating.
Some 85 of WHO's 193 member states have reported that they do not have access to H1N1 vaccine supplies, according to Hartl.
Susan Rice, U.S. ambassador to the United Nations, told reporters the announcement was in the shared interest of all nations.
"The speed and the scale of our global response will help minimize the overall impact of the pandemic 2009 H1N1 influenza and ensure our collective and common security in our increasingly interdependent world," Rice said, and encouraged other nations to join the effort.
The United States has on order 195 million doses of the swine flu vaccine, which is due to start arriving early next month.
Vaccine makers GlaxoSmithKline and Sanofi-Pasteur have also pledged 120 million doses to the WHO.