The World Health Organization (WHO) has confirmed five human bird flu cases in Vietnam, four of them fatal, the U.N. agency said in a statement.

The four, including two women, died between June 21 and August 3 while a fifth person, a 29-year-old man, had recovered, it said.

All five cases, which had been confirmed earlier by Vietnam-based laboratory tests, were from the country's north. They brought the total human infections in the Southeast Asian country since 2003 to 100 with 46 fatalities.

Three of Vietnam's 64 provinces -- two in the southern Mekong delta and one in the north -- are still on the government's current bird flu watchlist, the Agriculture Ministry said on Friday.

Bird flu has infected seven people in Vietnam so far this year and officials said the H5N1 virus could return in winter, starting in November.

The H5N1 virus remains mainly a virus of birds, but experts fear it could mutate into a form easily transmitted from person to person and sweep the world, killing millions.

Globally, the H5N1 virus has killed 199 people out of 327 known cases, according to a WHO tally. Hundreds of millions of birds have died or been slaughtered.