WHO Director-General Dr. Margaret Chan said she has decided to raise the level of pandemic alert from Phase 5 to Phase 6, which indicates that a global pandemic is underway.
Since the virus was first detected in April, 74 countries have reported 28,774 laboratory confirmed cases of the virus, with 144 deaths.
"This particular H1N1 strain has not circulated previously in humans. The virus is entirely new," Dr. Chan said. "The virus is contagious, spreading easily from one person to another, and from one country to another."
WHO Director-General Dr. Margaret Chan announces an influenza pandemic. (Photo courtesy WHO)
"Spread in several countries can no longer be traced to clearly-defined chains of human-to-human transmission. Further spread is considered inevitable," she said.
A characteristic feature of pandemics is their rapid spread to all parts of the world, said Dr. Chan. "Countries should prepare to see cases, or the further spread of cases, in the near future. Countries where outbreaks appear to have peaked should prepare for a second wave of infection."
Globally, Dr. Chan told journalists today, this pandemic, at least in its early days, will be of moderate severity. "On present evidence, the overwhelming majority of patients experience mild symptoms and make a rapid and full recovery, often in the absence of any form of medical treatment."
"Worldwide, the number of deaths is small," she said. "Each and every one of these deaths is tragic, and we have to brace ourselves to see more. However, we do not expect to see a sudden and dramatic jump in the number of severe or fatal infections."
"We recommend no closure of borders, no restrictions on travel, and no trade bans, she said.
Dr. Chan said she has conferred with leading influenza experts, virologists, and public health officials. In line with procedures set out in the International Health Regulations, she has sought guidance and advice from an Emergency Committee established for this purpose.
"On the basis of available evidence, and these expert assessments of the evidence, the scientific criteria for an influenza pandemic have been met," Dr. Chan declared. "The world is now at the start of the 2009 influenza pandemic."
"We have a head start. This places us in a strong position," said Dr. Chan. "But it also creates a demand for advice and reassurance in the midst of limited data and considerable scientific uncertainty."
No previous pandemic has been detected so early or watched so closely, in real-time, right at the very beginning, said the director-general. The world can now reap the benefits of investments over the last five years in pandemic preparedness that were developed to deal with the H5N1 virus, avian influenza.
"We still have H5N1 in Phase 3, said Dr. Chan. "This is the first time we have had two viruses in various stages of pandemic alert."
The H1N1 virus, also called human swine flu, can change rapidly so countries must be on high alert, Dr. Chan said.
Young or old, officials at the Buenos Aires airport required passengers on all flights from Mexico and the U.S. to wear supplied masks in the airport. (Photo credit unknown)
"Thanks to close monitoring, thorough investigations, and frank reporting from countries, we have some early snapshots depicting spread of the virus and the range of illness it can cause. We know, too, that this early, patchy picture can change very quickly. The virus writes the rules and this one, like all influenza viruses, can change the rules, without rhyme or reason, at any time."
The novel H1N1 virus preferentially infects younger people. In nearly all areas with large and sustained outbreaks, the majority of cases have occurred in people under the age of 25 years.
In some of these countries, around two percent of cases have developed severe illness, often with very rapid progression to life-threatening pneumonia. Most cases of severe and fatal infections have been in adults between the ages of 30 and 50 years.
"This pattern is significantly different from that seen during epidemics of seasonal influenza, when most deaths occur in frail elderly people," Dr. Chan said.
Many, though not all, severe cases have occurred in people with underlying chronic conditions. Based on limited, preliminary data, conditions most frequently seen include respiratory diseases, notably asthma, cardiovascular disease, diabetes, autoimmune disorders, and obesity, she said.
Around one third to half of the severe and fatal infections are occurring in previously healthy young and middle-aged people.
"Without question, pregnant women are at increased risk of complications. This heightened risk takes on added importance for a virus, like this one, that preferentially infects younger age groups," said the director-general.
"Finally, and perhaps of greatest concern," she said, "we do not know how this virus will behave under conditions typically found in the developing world. To date, the vast majority of cases have been detected and investigated in comparatively well-off countries."
WHO has been in close contact with influenza vaccine manufacturers. Production of vaccines for seasonal influenza will be completed soon, and Dr. Chan said manufacturers' full capacity will be available to ensure the largest possible supply of pandemic vaccine in the months to come.
Dr. Chan said a vaccine that provides immunity against the new H1N1 virus will likely be available sometime in September.
Eventually, people will develop immunity to this virus, said WHO assistant director-general Dr. Keiji Fukuda. "We expect this period in which the virus spreads will go on for several months, after that we expect to see immunity build up in the population," he told journalists today. "Then the heightened alert switches over to being a long-term influenza virus."
"We're talking about a marathon, not a sprint," he said. "All countries will adjust to this."
Copyright Environment News Service (ENS) 2009. All rights reserved.