New Delhi: Preliminary analysis of the A/H1N1 virus strain, or the swine flu virus, that has killed 61 people and infected at least 5,000 in 30 countries suggests that it spreads faster than typical seasonal flu epidemics, making it comparable to major epidemics such as the Spanish flu and the Asian flu that had swept the world in the last century.

These findings are to be published in Friday’s issue of Science.

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“Our early analysis would suggest this is going to be an outbreak comparable to that of 20th century pandemics regarding the extent of its spread—it’s very difficult to quantify the human health impact at this stage, however," said study author Neil Ferguson of Imperial College London, in a press statement.

Ferguson and his collaborators, part of the World Health Organization’s (WHO) Rapid Pandemic Potential Assessment Collaboration, determined that 6,000–32,000 individuals had been infected in Mexico by late April. The team also used epidemiological data and information about the virus’ genetic diversity to determine that the swine flu virus has a basic reproductive rate of 1.2-1.6, a number that shows how easily the virus spreads within a population. The seasonal flu, which hits countries, typically hovers around 1.2, whereas the second, more severe wave of the 1918 flu reached about 2.

Worst-hit: Schoolchildren in Mexico. The swine flu virus, especially in Mexico, is characterized by sustained human-to-human transmission. Jorge Dan / Reuters

However, the researchers emphasize that these are preliminary estimates and the results of the study are only meant to validate WHO’s decision to categorize the pandemic as a level 5.

“The information we have is still incomplete, but this can help lay out a scientific basis for political decisions," said Ferguson. “The characteristics of the ongoing epidemic they examined, mostly in Mexico, clearly has sustained human-to-human transmission and we know this is also true in the US. It says that, yes, it was an appropriate response on the part of WHO to move the alert to level 5."

Experts in India say the findings are significant. “Though preliminary, it is certainly a good piece of research," said Shahid Jameel, who’s an expert on viruses, and a professor at the International Centre for Genetic Engineering and Biotechnology, New Delhi. “However, this is a modelling study and based on a computer simulation. The results of such a study are extremely dependent on the kind of data that is input. You have to keep that in mind."

Scientists are non-committal on what these findings mean for possible mortality rates in India, as the country doesn’t maintain a database of seasonal swine flu infections. “Since we don’t have such a database, it wouldn’t be scientific to extrapolate mortality rates in Mexico to India," said Shobha Broor, head, department of microbiology, All India Institute of Medical Sciences.