1976 U.S. outbreak
On February 5, 1976, an army recruit at Fort Dix said he felt tired and weak. He died the next day and four of his fellow soldiers were later hospitalized. Two weeks after his death, health officials announced that swine flu was the cause of death and that this strain of flu appeared to be closely related to the strain involved in the 1918 flu pandemic. Alarmed public-health officials decided that action must be taken to head off another major pandemic, and they urged President Gerald Ford that every person in the U.S. be vaccinated for the disease. The vaccination program was plagued by delays and public relations problems, but about 24% of the population had been vaccinated by the time the program was canceled.
About 500 cases of Guillain-Barré syndrome, resulting in death from severe pulmonary complications for 25 people, were probably caused by an immunopathological reaction to the 1976 vaccine. Other influenza vaccines have not been linked to Guillain-Barré syndrome, though caution is advised for certain individuals, particularly those with a history of GBS.
The 2009 swine flu outbreak is the spread of a new strain of H1N1 influenza virus that began in March of 2009. Localized outbreaks of influenza-like illness (ILI) were detected in three areas initially in Mexico and soon after in the United States. Following the discovery of the new strain in the United States, its presence was quickly confirmed in multiple nations across several continents. There have been over 1,600 suspected cases. Because it is not possible to confirm every one of such cases as being caused by an influenza virus, the World Health Organization (WHO) refers to them collectively as influenza-like illnesses (ILI).
The new strain is derived in part from human influenzavirus A (subtype H1N1), and in part from two strains of swine influenza as well as an avian influenza. In April both the WHO and the United States Centers for Disease Control and Prevention (CDC) expressed serious concerns about this novel strain, because it apparently transmits from human to human, has had a relatively high mortality rate in Mexico, and because it has the potential to become a flu pandemic.
On April 25, 2009, the WHO determined the situation to be a formal "public health emergency of international concern", with knowledge lacking in regard to "the clinical features, epidemiology, and virology of reported cases and the appropriate responses". Government health agencies around the world also expressed concerns over the outbreak and are monitoring the situation closely.