The United States and several other nations are reporting higher rates of the flu compared with past seasons.

American health officials say the winter outbreak is expected to be one of the most severe in 15 years, with up to 34 million people infected. Across the U.S., 1 in 15 doctor visits last week were related to the flu – the highest level since the 2009 swine flu pandemic. Before that outbreak, the last time the U.S. experienced such high levels of seasonal flu was in 2003-2004.

The U.S. Centers for Disease Control and Prevention or CDC said last week that flu cases are currently active in all U.S. states except for Hawaii. All remaining 49 states have reported widespread flu activity for the past three weeks.

Officials say most U.S. cases of the flu, also called influenza, involve the H3N2 flu virus, the same kind mainly seen last winter.

The CDC said the flu has caused nearly 12,000 hospitalizations and killed 37 children. The CDC does not track adult flu deaths directly. But the highest hospitalization rates have been among people 65 years and older.

Flu is a contagious illness that causes such symptoms as fever, cough, headaches and tiredness. Most people who catch the flu get better within a week or two. But some people develop more serious conditions caused by an infection involving the nose, throat or lungs.

The flu season is usually highest in February and officials say activity has already begun to slow in some parts of the U.S. The CDC recommends a flu vaccine for everyone older than 6 months. But officials said this year's vaccine is only about 30 percent effective in preventing infection.

Flu outbreaks in Koreas, Japan, and Britain

In Asia, North and South Korea have reported separate outbreaks of different strains of influenza. The rise in cases comes less than two weeks before thousands of visitors from around the world arrive for the 2018 PyeongChang Winter Olympics in the South.

North Korea's Ministry of Public Health reported more than 80,000 confirmed cases of the influenza strain H1N1 between December 1, 2017 and January 16, 2018. The Red Cross said North Korean health officials reported three children and one adult have died so far in the outbreak.

In the South, officials announced last weekend they discovered a serious strain of the H5N6 avian influenza on a chicken farm near Seoul. About 500,000 chickens and 450,000 eggs were to be destroyed at farms where the virus was found.

In Japan, the health ministry reported flu cases reached a record high 2.83 million cases last week. The average number of patients per medical facility was 52, Japan's Kyodo news agency reported. This is the highest number since such data was first collected in 1999. The ministry said the illness hit children and young people especially hard, with more than 100 schools closed.

In Britain, health officials recently reported the country was having its worst flu season in seven years. Official government data shows there have also been nearly three times more flu deaths this season compared to last. At least 155 deaths blamed on the flu have been confirmed since last October.

However, the country's health agency Public Health England reported last week the nationwide rate of people seeking treatment with flu-like symptoms had stabilized. Officials said the hospitalization rate for flu was down 12 percent, leading health officials to say the number of seasonal cases may have peaked.

Are we ready for the next pandemic?

The possibility of future worldwide pandemics was discussed by health officials attending last week's meeting of the World Economic Forum in Davos, Switzerland. One warning came from Elhadj As Sy, head of the International Federation of Red Cross and Red Crescent Societies. The official told the French Press Agency AFP that he believes pandemics "are becoming a real threat to humanity."

Officials gathered for a discussion called "Are We Ready for the Next Pandemic?" One speaker was Sylvie Briand, a specialist with the World Health Organization, or WHO, who warned about the dangers of a possible future disease similar to Ebola, Zika or SARS. "We know that it is coming, but we have no way of stopping it," she said.

I'm Bryan Lynn.

Bryan Lynn wrote this story for VOA Learning English, based on reports from VOA News, the Associated Press, Reuters and other sources. Hai Do was the editor.