Pandemia de influenza porcina (H1N1). Importante información preliminar para la comprensión del desarrollo de la situación, OMS

El número de casos humanos de la pandemia H1N1 del 2009 se mantiene incrementando sustancialmente en muchos países, aun en algunos que ya han estado siendo afectados durante un tiempo. Nuestro conocimiento sobre la enfermedad continúa desarrollándose a medida que más países son afectados, que la propagación a nivel de la comunidad se extiende en países ya afectados y que la información es compartida globalmente.
Muchos países con extensa transmisión en la comunidad ahora solo analizan las muestras de personas infectadas y han redirigido sus esfuerzos de vigilancia a monitorear y reportar las tendencias. Este cambio ha sido recomendado por la OMS porque, a medida que la pandemia progresa, monitorear las tendencias en la actividad de la enfermedad puede resultar mejor siguiendo las tendencias de los casos enfermos que tratando de hacer análisis todas las personas infectadas, algo que puede agotar seriamente los recursos nacionales. Se mantiene como de la más alta prioridad determinar qué grupos están en más alto riesgo de enfermedad severa de manera que deben ser tomadas medidas para su mejor protección.

Además de la información sobre la vigilancia, la OMS cuenta con los resultados de estudios clínicos y de investigaciones especiales y otras informaciones brindadas a través de frecuentes teleconferencias de expertos de varios países sobre aspectos clínicos, virológicos y epidemiológicos de la pandemia, para obtener una visión global del desarrollo de la situación.
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Average age of cases increasing
In most countries the majority of pandemic (H1N1) 2009 cases are still occurring in younger people, with the median age reported to be 12 to 17 years (based on data from Canada, Chile, Japan, UK and the United States of America). Some reports suggest that persons requiring hospitalization and patients with fatal illness may be slightly older.

As the disease expands broadly into communities, the average age of the cases is appearing to increase slightly. This may reflect the situation in many countries where the earliest cases often occurred as school outbreaks but later cases were occurring in the community. Some of the pandemic disease patterns differ from seasonal influenza, where fatal disease occurs most often in the elderly (>65 years old). However, the full picture of the pandemic’s epidemiology is not yet fully clear because in many countries, seasonal influenza viruses and pandemic (H1N1) 2009 viruses are both circulating and the pandemic remains relatively early in its development.

Although the risk factors for serious pandemic disease are not know definitively, risk factors such as existing cardiovascular disease, respiratory disease, diabetes and cancer currently are considered risk factors for serious pandemic (H1N1) 2009 disease. Asthma and other forms of respiratory disease have been consistently reported as underlying conditions associated with an augmented risk of severe pandemic disease in several countries.

A recent report suggests obesity may be another risk factor for severe disease. Similarly, there is accumulating evidence suggesting pregnant women are at higher risk for more severe disease. A few preliminary reports also suggest increased risk of severe disease may be elevated in some minority populations, but the potential contributions of cultural, economic and social risk factors are not clear.
Vaccine situation
The development of new candidate vaccine viruses by the WHO network is continuing to improve yields (currently 25% to 50 % of the normal yields for seasonal influenza for some manufacturers). WHO will be able to revise its estimate of pandemic vaccine supply once it has the new yield information. Other important information will also be provided by results of ongoing and soon-to be-initiated vaccine clinical trials. These trials will give a better idea of the number of doses required for a person to be immunized, as well as of the quantity on active principle (antigen) needed in each vaccine dose.

Manufacturers are expected to have vaccines for use around September. A number of companies are working on the pandemic vaccine production and have different timelines.

Source: World Health Organization