MEXICO CITY, Mexico (CNN) -- Mexico lowered its health alert level Monday, citing improvements in the battle against swine flu.
The level was lowered from red, or "high," to orange, or "elevated."
"The measures we have taken, and above all the public's reaction, have led to an improvement," Mexico City Mayor Marcelo Ebrard said at a news conference.
"But I insist that the virus is still present, that we need to remain on alert, and the resumption of activities will be little by little, not all at once."
But U.S. health officials cautioned that the H1N1 virus is still on an "upswing" in the United States. And the World Health Organization warned that after the number of cases begins to subside, the swine flu could return this year "with a vengeance."
The number of confirmed cases worldwide was expected to cross the 1,025 mark Monday. Earlier in the day, the WHO reported at least 985 cases across 20 countries. There were 26 reported deaths, including one in the United States, a Mexican toddler who was visiting relatives in Texas.
The U.S. Centers for Disease Control and Prevention reported 226 cases across 30 states.
New York Mayor Michael Bloomberg announced Monday that 10 more cases not counted in the CDC total have been confirmed, bringing New York City's total to 73. One school -- P.S. 177 in Queens -- remained closed Monday because of five confirmed cases there.
But St. Francis Prep School in Queens re-opened its doors. -snip-
In Atlanta, Georgia, the CDC cautioned Americans not to reduce their vigilance.
"I'm heartened by the Mexican authorities' reports, but I am very cautious," Dr. Anne Schuchat, the CDC's interim deputy director for public health, said Sunday. "I know that influenza can be surprising, and the time course here in the United States is later. We believe we're just on the upswing here."
Because cases began earlier in Mexico, it would make sense for that country to see its peak sooner, she explained.
A spokeswoman for the U.S. Marine Corps base at Twentynine Palms in California said two new cases of the flu were confirmed by the CDC late Sunday. The two Marines show no symptoms but are being kept in isolation, spokeswoman Jennie Haskamp said. One other case had been confirmed at the base.
The U.S. Defense Department also reported that a crew member stationed aboard the amphibious transport dock ship USS Dubuque in San Diego, California, was confirmed to have swine flu and was ashore. The department said there were 13 other "probable" cases among Dubuque crew.
California officials were looking into a suspected case at a prison. Authorities suspended visitation and other "non-essential activities" at Centinela State Prison in Imperial County after an inmate was suspected of having the virus. The case has not been confirmed.
As hard as they are pushing to contain the outbreak, health officials in the United States and worldwide are working around the clock to develop a vaccine. -snip-
Ecuador tightened its borders after one person tested positive for the virus in neighboring Colombia.