The World Health Organization says a vaccine is the best tool against swine flu despite reports of a few minor side effects in China.

Spokesman Gregory Hartl says WHO has seen reports of four people out of 39,000 vaccinated against H1N1 in China who have had side effects like muscle cramps and headache.

Hartl says such effects are to be expected.

He says people — especially health care workers — should be encouraged to get the vaccine.

Hartl says the current formulation is among the safest vaccines that WHO has seen.

He said Tuesday that the vaccination campaign will soon move to Australia, the United States and parts of Europe.