Public Health: WHO declares A(H1N1) a pandemic

Dr Margaret Chan, Director-General of the World Health Organisation, issued a statement yesterday confirming that "we are at the start of 2009 Influenza Pandemic."

In her speech she included the following points:

- This particular H1N1 strain has not circulated previously in humans. The virus is entirely new.

- The virus is contagious, spreading easily from one person to another, and from one country to another. As of today, nearly 30,000 confirmed cases have been reported in 74 countries.

She indicated that low reporting is not confirmation of low incidence of the virus:

- With few exceptions, countries with large numbers of cases are those with good surveillance and testing procedures in place.

The spread of the virus is, if not out of control, certainly not under control:

- Spread in several countries can no longer be traced to clearly-defined chains of human-to-human transmission. Further spread is considered inevitable.

Since SARS in 2002, improved monitoring means that the virus has been identified early and watched closely:

- No previous pandemic has been detected so early or watched so closely, in real-time, right at the very beginning. The world can now reap the benefits of investments, over the last five years, in pandemic preparedness.

- we have good reason to believe that this pandemic, at least in its early days, will be of moderate severity. As we know from experience, severity can vary, depending on many factors, from one country to another. 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.

The pattern of infection is unusual:

- We know that 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. 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.

- 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.

- At the same time, it is important to note that around one third to half of the severe and fatal infections are occurring in previously healthy young and middle-aged people.

- 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 continues to recommend no restrictions on travel and no border closures.