[Main features of the new influenza virus a pandemic (H1N1)]. / Principales características de la pandemia por el nuevo virus influenza A (H1N1).

At the end of March 2009, a new influenza virus A (H1N1) of porcine origin was isolated in two children from California presenting flu-like clinical syndrome. This virus was initially disseminated in Mexico and US and then worldwide. Eight weeks later, it had reached 74 countries with almost 30,000 cases and had caused 145 deaths. The virus had also sustained community transmission in 6 countries. On June 11th, WHO stated the onset of a pandemic. The genetic combination of this virus is completely new, containing five segments of porcine origin, two avian, one human and a HA hemaglutinin adapted for human transmission, which is genetically and antigenically different compared with the H1N1 seasonal virus. Its transmissibility is slightly higher than the one observed in seasonal influenza and similar to previous pandemics. Its pathogenicity and virulence are low. Clinical manifestations are similar to seasonal influenza, with spontaneous resolution. Nevertheless, the variety of symptoms is large and range from asymptomatic to severe fatal pneumonia. The affected population is mainly young, aged under 30 years. Less than a half of the hospitalized patients in US and of the fatal cases in Mexico had concomitant chronic diseases or other baseline conditions. A specific monovalent vaccine against the virus is currently being produced in order to prevent and control the infection through the reduction of susceptible population.

Principales características de la pandemia por el nuevo virus influenza A (H1N1) / Main features of the new influenza virus a pandemic (H1N1)

A finales de marzo de 2009 fue aislado un nuevo virus influenza A (H1N1) de origen porcino en 2 niños de California con síntomas de gripe. Dicho virus se diseminó inicialmente por México y EE.UU., y después internacionalmente. A primeros de junio la infección había alcanzado 74 países, producido cerca de 30.000 casos y 145 muertes y poseía una propagación comunitaria sostenida en 6 países. El 11 de junio la Organización Mundial de la Salud (OMS) declaró establecida la situación de pandemia. La combinación de segmentos genéticos del nuevo virus nunca había sido vista antes. Contiene 5 segmentos de origen porcino, 2 aviares y 1 humano, y posee una hemaglutinina HA adaptada a la transmisión humana, que genética y antigénicamente diverge respecto a la del virus H1N1 hasta ahora circulante. Su transmisibilidad es ligeramente superior a la de la gripe estacional, y equivalente a la de las anteriores pandemias. Su patogenicidad y virulencia son bajas. El cuadro clínico es similar al típico de la gripe estacional, con curación espontánea, si bien el espectro clínico es extenso, pues va desde casos asintomáticos hasta neumonía grave o mortal. La población afectada ha sido predominantemente joven, de menos de 30 años. Menos de la mitad de los pacientes hospitalizados en EE.UU. y de los casos mortales en México presentaban enfermedades crónicas o procesos de base concomitantes. Para la prevención y control de la infección, a través de la reducción de susceptibles, se ha dispuesto el uso de una vacuna monovalente específica contra el virus (AU)

At the end of March 2009, a new influenza virus A (H1N1) of porcine origin was isolated in two children from California presenting flu-like clinical syndrome. This virus was initially disseminated in Mexico and US and then worldwide. Eight weeks later, it had reached 74 countries with almost 30,000 cases and had caused 145 deaths. The virus had also sustained community transmission in 6 countries. On June 11th, WHO stated the onset of a pandemic. The genetic combination of this virus is completely new, containing five segments of porcine origin, two avian, one human and a HA hemaglutinin adapted for human transmission, which is genetically and antigenically different compared with the H1N1 seasonal virus. Its transmissibility is slightly higher than the one observed in seasonal influenza and similar to previous pandemics. Its pathogenicity and virulence are low. Clinical manifestations are similar to seasonal influenza, with spontaneous resolution. Nevertheless, the variety of symptoms is large and range from asymptomatic to severe fatal pneumonia. The affected population is mainly young, aged under 30 years. Less than a half of the hospitalized patients in US and of the fatal cases in Mexico had concomitant chronic diseases or other baseline conditions. A specific monovalent vaccine against the virus is currently being produced in order to prevent and control the infection through the reduction of susceptible population (AU)