Flu fight

All three of the major flu pandemics of the 20th century - including the Spanish Flu of 1918 - began in similar fashion to the current H1N1 type A influenza, known as swine flu.

The pandemics began as relatively mild, late spring outbreaks in the northern hemisphere and affected healthy adults rather than the elderly and very young, who tend to be hardest hit by the flu, experts pointed out on Tuesday.

"It is disconcerting that in 1918 there was a summer outbreak that was fairly mild," John Oxford, a virologist at the Royal London Hospital, told the AFP news agency. "It should have been a warning for the big wave, that came in the fall and winter."

Back with a vengeance

Fear of genetic mutations and the virus' ability to be transmitted from person to person were among the reason the World Health Organization increased its pandemic alert status to Level 5, one step short of its highest warning level.

WHO Director-General Margaret Chan also expressed her fear that the flu could return "with a vengeance." She added, however, that the virus had not become a pandemic, "No one can say right now how the pandemic will evolve or indeed whether we are going into a pandemic."

Increasing the WHO alert to Level 6 would mean that a global outbreak of swine flu is under way. Level 5 calls for national governments to enact pandemic preparation plans.

While the swine flu, in its current incarnation, bears some resemblance to the Spanish flu, it lacks some of the genes that made the 1918 virus so lethal, according to the US Center for Disease Control and Prevention.

Medical advances improve treatment

Health officials have also said the virus' relatively mild effects outside of Mexico, where the infection originated, could be a sign that the current swine flu infections will not take on pandemic proportions.

Seasonal flu strikes 57,000 to 96,000 people each week, and leaves 4,800 to 9,600 dead. The A(H1N1) swine flu virus has infected 1,124 people and killed 26 worldwide over the last 10 days, the WHO said.

While experts, including Oxford, have said a second wave of the virus is extremely likely, there is no guarantee it would be more lethal and even a worst-case scenario would not reach 1918 proportions.

"We will have totally failed in our preparation for this if we get a 1918 scenario," Oxford said. "We've got antiviral drugs and the knowledge base about transmission."

Modern antibiotics could also save millions of lives. Some 60 percent of deaths in 1918 were due to secondary, bacterial infections resulting in pneumonia and other respiratory disease.

The most basic flu precautions, including hand washing, avoiding close contact with the sick and covering the nose and mouth when coughing and sneezing, should be followed as effective way of limiting the virus' transmission, according to the World Health Organization.