WASHINGTON - President Bush received a smallpox vaccination Saturday, fulfilling a promise he made when he ordered inoculations for about a half-million U.S. troops.

He showed no immediate ill effects from the vaccine, which can sicken and in rare cases kill those who get it. An hour after being inoculated in his left arm, Bush was carrying his dog in that arm as he walked to his helicopter and left for Camp David.

Bush announced Dec. 13 that the vaccine would be mandatory for those forces in "high-risk" parts of the world.

"As commander in chief, I do not believe I can ask others to accept this risk unless I am willing to do the same," Bush said then.

"He feels fine and there are no side effects," Bush spokeswoman Jeanie Mamo said. Bush smiled and waved at well-wishers as he walked across the South Lawn and departed for a long weekend at Camp David.

He will be there for five days, accompanied by a doctor who can monitor him for side effects.

Typical side effects from the vaccine, which is made with a live virus, include sore arms, fever and swollen glands. In an experimental trial under way in Nashville, Tenn., about 10 percent of people experienced extreme discomfort, with fatigue, fever, loss of appetite and other flu-like symptoms that lasted a day or two.

Also Saturday, in his weekly radio address, Bush called on Americans to help the poor and keep U.S. troops in their thoughts.

"We all share a responsibility to help, both through our government and through individual acts of compassion," the president said. "In this season of giving, I hope all Americans will look for opportunities to donate and volunteer where the need is greatest."

The president and first lady Laura Bush were spending Saturday through Christmas Day at Camp David, then flying to their ranch in Crawford, Texas. They are to return to Washington on Jan. 4.

Joining them are daughters Barbara and Jenna and Bush's mother-in-law, Jenna Welch.