"We are now moving into the postpandemic period," said WHO Director-General Margaret Chan, MD. "The new H1N1 virus has largely run its course."
The 2009 H1N1 influenza virus has not disappeared, Dr. Chan noted, and it still poses a risk for serious illness, especially for young children, pregnant women, and persons with respiratory or chronic illnesses. However, the agency expects the virus to circulate and behave as one of several seasonal varieties in years to come, and not to dominate the pack.
"Many countries are reporting a mix of influenza viruses, again as is typically seen during seasonal epidemics," said Dr. Chan.
On June 11, 2009, WHO declared that transmission of the novel influenza virus had morphed into a full-blown pandemic, which is level 6 on a scale that the agency uses to classify influenza outbreaks. The postpandemic phase, which is at the end of the scale, indicates that influenza activity is at seasonal levels.
Earlier today, an emergency committee that advises Dr. Chan on the pandemic convened by teleconference and concluded that "the world was no longer experiencing an influenza pandemic, but that some countries continue to experience significant H1N1 (2009) epidemics," according to WHO.
During the spring and summer, virus transmission has dramatically tapered off in the Northern Hemisphere. WHO said on Tuesday that it had delayed making a decision on whether the pandemic was over until the emergency committee could assess the virus' behavior in the southern hemisphere during its winter influenza season. The committee concluded that for both hemispheres, 2009 H1N1 virus activity "no longer represented an extraordinary event requiring immediate emergency actions on an international scale."
Pandemic Less Deadly Than Feared Because of Hard Work, Good Luck
WHO has been accused in some quarters of declaring a "fake" pandemic, given that the H1N1 virus has killed fewer people than seasonal flu viruses on an annual basis in countries such as the United States. The agency has denied intentionally exaggerating the pandemic's severity for ulterior motives, such as boosting sales for vaccine manufacturers. Nevertheless, Dr. Chan said today that the pandemic "has turned out to be much more fortunate than what we feared a little over a year ago."
Dr. Chan attributed the fortunate outcome in the pandemic saga to a combination of hard work and "pure good luck."
"The virus did not mutate during the pandemic to a more lethal form," she said. "Widespread resistance to oseltamivir [Tamiflu; Roche Inc] did not develop. The vaccine proved to be a good match with circulating viruses and showed an excellent safety profile."
On another positive note, Dr. Chan said that infection rates of 20% to 40% in some areas have created a level of protective immunity, augmented by good vaccination coverage in many countries.
However, public health authorities should continue to remain vigilant about the 2009 H1N1 virus instead of letting down their guard, she said. For one thing, a small proportion of pandemic influenza patients — including young, healthy ones — experienced a severe form of primary viral pneumonia that was very hard to treat. Dr. Chan said nobody knows whether this pattern will continue during the postpandemic phase.
In addition, WHO expects the virus to change as a result of antigenic drift, lowering the protection offered by the community-wide immunity that has developed so far. At the same time, significant influenza outbreaks could occur in areas that got off lightly during the pandemic.
The WHO prescription for the postpandemic era mirrors its advice during the pandemic itself:
- Clinicians should vaccinate individuals against the 2009 H1N1 virus with either a monovalent vaccine or a trivalent seasonal vaccine that contains a strain of the pandemic virus (the United States will use the latter this fall).
- Good personal hygiene is still in order — clinicians should advise their patients to continue to cover their mouths when they sneeze or cough and to diligently wash their hands.
- As during the pandemic, patients who have a severe or deteriorating case of influenza should be treated with oseltamivir immediately, and clinicians should prescribe either oseltamivir or zanamivir (Relenza; GlaxoSmithKline) as soon as possible for patients who are higher risk for severe or complicated influenza.