(CNN) -- The World Health Organization on Friday reported 2,500 confirmed cases of swine flu in 25 countries, with 44 deaths from the disease.
A researcher investigates swine flu at the Centers for Disease Control and Prevention in Atlanta, Georgia.
In the United States, the total number of confirmed cases of the H1N1 virus, as swine flu is officially called, nearly doubled to 1,639 from the day before, with reports coming from 43 states, the Centers for Disease Control and Prevention reported.
The U.S. Navy said Friday that 12 crew members aboard the USS Dubuque have been diagnosed with swine flu.
The amphibious transport dock ship had been due to deploy on June 1 to the South Pacific on a humanitarian mission, Cmdr. Joseph Surette, a Navy spokesman, said Tuesday.
The ship was being scrubbed and disinfected, and its remaining 370 crew members were given Tamiflu as a precaution, Surette said.
Navy officials said the ship could still be deployed in an emergency, but would remain in port in San Diego, California, until commanders determine the crew is suitable to deploy.
Dr. Sylvie Briand, acting director of the Global Influenza Program for the World Health Organization, said the agency will remain at pandemic alert level 5 -- one step away from its highest level -- because while there are an increasing number of cases, there is no evidence of the community transmission outside North America that would push the alert to level 6.
Of the 44 deaths reported, two were in the United States and 42 in Mexico, which has the highest concentration of swine flu cases, with more than 1,100.
President Obama, speaking on the H1N1 virus during a town hall meeting for Latinos, said Americans should continue to take basic precautions such as frequently washing their hands. He also said the country should prepare for a particularly tough flu season this fall.
"The virus may not have been as virulent as we once feared, but we're not out of the woods yet," Obama said.
Briand of WHO said many of the new cases being reported are imported -- returning travelers bringing them into their countries -- and cases resulting from close contact with those already infected, such as family members.
Meanwhile, Britain's health secretary announced Friday that his country's Health Protection Agency has sequenced the full genetic code of the H1N1 virus, the first step in producing a European prototype of a swine flu vaccine.
"This is critical in understanding how the virus operates and identifying the crucial parts of the virus that can be used in vaccine manufacture," said a statement from the agency.
"Researchers hope that European manufacturers will be able to take delivery of candidate vaccine prototypes in the coming months so preliminary steps to mass vaccine production can begin," the statement said.