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Pandemic 6 Designation Raises Pandemic Concerns
It means the swine flu virus is spreading in at least two regions of the world with rising cases being seen in the UK, Australia, Japan and Chile.
The above comments describe the decision of WHO to raise the pandemic level from 5 to 6, the highest level. Thus, the 2009 pandemic is the first since 1968, when H3N2 replaced H2N2, which had replaced H1N1 in 1957.
However, the 2009 pandemic involves swine H1N1, and the last time swine H1N1 moved into a human population was in 1918.
The parallels between the 2009 pandemic and the 1918 pandemic are striking; Both began as a mild infection in the spring and targeted previously healthy young adults. In the fall of 1918, the virus was much more deadly, leading to the death of 20-50 million people, most of which were previously healthy young adults.
In 2009, a similar pattern was seen in Mexico in mid-April. At the same time the swine H1N1 was detected in children in southern California. However, the patients in southern California were over 100 miles apart and had no relationship with each other, or contact with swine. Thus, it was clear that in later March / early April, there was sustained community transmission in the United States and Mexico. Shortly thereafter, sequence analysis demonstrated that the H1N1 in both countries was the same (a swine H1N1 that had a human PB1, avian PB2, and swine origins for the six remaining gene segments).
Under the earlier pandemic phasing system, the discovery of sustained transmission would have generated a phase 6 designation two months ago. The earlier system defined phase 3,4, and 5 by increased transmission, and phase 6 represented sustained transmission, which was unlikely to be halted.
The new system moved sustained transmission down to phase 4 and then defined phase 5 and 6 as geographical spread due to the sustained transmission, which was a minor variation of the sustained transmission theme.
The new system also led to surveillance at airports, long after the virus had spread worldwide (see updated map). However, countries largely missed the internal spread because efforts were focused on border entry. Since the virus produced mild symptoms, the internal spread was largely missed and as surveillance moves toward more widespread detection the extent of the earlier spread nwill be clear.
It was this focus on airports that minimized the data on community spread, so the two month delay had much more to do with the revised phasing and misguided testing, than the actual spread of the virus.
At this point, there is little that will stop the spread prior to widespread use of an effective vaccine, However, the large reservoir of swine H1N1 in a human population, involving the northern hemisphere where the virus has little completion by seasonal flu, and the southern hemisphere, where the swine virus is displacing seasonal flu, raises concerns that when the new vaccine is ready for the 2009/2010 season, the swine H1N1 will have evolved away from the vaccine, as it adapts to its new host and natural immunity in its new host.
Thus, the two month delay in the pandemic 6 declaration may prove to be quite hazardous to the world's health.