What more do we know about A/H1N1 compared with two months ago?

Much more is now known about the virus’s transmission characteristics, what happens in the clinical setting, and its mortality and morbidity. The UK Health Protection Agency (HPA) has undertaken a project, called the first few hundred (FF100) cases surveillance system, that has collected detailed data on 350 cases of influenza and the patients’ close contacts. Results have not yet been published, but the work has allowed the agency to gather information on transmissions within households, duration of illness, and clinical picture. The data have been used by the agency’s modellers for forward planning and potential impact. The HPA says that this virus is similar to seasonal flu. Taking oseltamivir (Tamiflu) is not a pleasant experience, with side effects that include nausea, diarrhoea, and hallucinations.

According to the World Health Organization the 2009 influenza pandemic has spread internationally with unprecedented speed. In past pandemics, flu viruses have needed more than six months to spread as widely as the new H1N1 virus, which has spread in less than six weeks. However, international travel is far more common than it was in the times of the previous pandemics in 1918, 1957, and 1968, and techniques to measure it now are much more sophisticated (N Engl J Med 2009;361:279-85, doi:10.1056/NEJMra0904322).

Researchers from Imperial College London in a study published in the BMJ have called for better estimates of case fatality ratio because the methods currently being used could overestimate or underestimate the numbers (BMJ 2009;339:b2840, doi:10.1136/bmj.b2840). The study shows that the virus is not becoming more virulent.

The Department of Health and various research councils have worked together to …