In early 2009, Mexico was the epicenter of a mysterious outbreak. A severe respiratory illness was affecting young people, contrary to seasonal viruses that often attack the elderly.
Health officials in Mexico and the United States were puzzled by a virus that combined elements of swine, avian and human influenza.
It was nicknamed Swine Flu, although a few months later public health experts began calling it by its proper name: H1N1.
Because Mexico is a popular tourist destination, Swine Flu quickly spread beyond North America to parts of Europe and Asia.
Dr. Margaret Chan, Director General of the World Health Organization (WHO), began a series of daily briefings to track H1N1 as it spread around the globe.
On June 11th, she announced the WHO was raising it to a pandemic.
"The virus is spreading under a close and careful watch," she said. "No previous pandemic has been detected so early or watched so closely, in real-time, right at the very beginning."
The WHO authorized drug manufacturers to begin testing possible vaccines, and the first human trials began a month later.
By October, the first batches were distributed to health care workers, pregnant women, young people and those with underlying medical conditions.
Dr. Anne Schuchat is director of the U.S. Centers for Disease Control and Prevention.
"As the supply increases, we do think that access and convenience and ease of getting vaccinated will improve," she said
By late December, WHO reported that more than 10,000 people had died from H1N1. Most of those deaths occurred in North America.
WHO says many countries have stopped counting the people with milder cases.
The virus appeared to be leveling off in North America and Europe by year's end. But some experts say it could come back in a third wave early next year.
In the United States in 2009, new recommendations on mammograms by a government appointed panel of experts fueled a controversy around breast cancer and how to prevent it.
For decades, American women were urged to get yearly mammograms, starting at age 40, as part of screening for breast cancer.
But the U.S. Preventive Services Task Force advised women in their 40s to delay their first mammogram until age 50, and after 50, schedule the x-ray every other year.
By late November, many American doctors and women said they were unhappy with the new guidelines.
Doctors like Sharon Rosenbaum Smith of St. Luke's Roosevelt Hospital in New York said they would advise patients to ignore the recommendations.
"They need to start getting mammograms at age 40," she said. "Mammograms pick up cancers when they're smaller."
Feeling the backlash, Health and Human Services (HHS) Secretary Kathleen Sebelius advised patients to stay calm and talk with their doctor.
"Figure out your own health situation with your doctor, your family history. Those are the really important ingredients," said HHS Secretary Sebelius.
As 2009 came to a close, suicides in the U.S. Army reached record levels. U.S. Army personnel predicted the suicide rate would be higher than the total in 2008. The Army launched a study into possible causes.
Vice Chief of Staff, General Peter Chiarelli, said military personnel must be more aggressive in getting treatment for mentally ill soldiers.
"It is absolutely unacceptable to have individuals suffering in silence because they're afraid their peers or superiors will make fun of them, or worse, it will adversely affect their careers," he said.
The year 2009 did produce some hopeful news. In September, the United Nations said the estimated number of deaths of children under age five had dropped from the previous year.
A UN report said it was the first time that deaths of children had dropped below nine million.
More immunizations, greater use of insecticide-treated nets to prevent malaria, programs to promote breastfeeding and better treatment of diarrhea and pneumonia were cited as reasons.