The current pandemic of H1N1 influenza, the first cases of which were detected in Mexico in March 2009, has extended worldwide with astonishing speed, matched only by the speed of response by health authorities and the pharmaceutical industry. On April 27, slightly a month after the first cases were detected, the World Health Organization raised the pandemic alert level to phase 4, indicating confirmed human-to-human transmission of the virus resulting in community-level outbreaks. Just two days later, WHO raised the pandemic alert level to phase 5, thus acknowledging efficient community-level human-to-human transmission of the virus in at least two countries within a single WHO region. On June 11, the WHO raised the level of influenza pandemic alert from phase 5 to phase 6, reflecting the fact that, in addition to the criteria defined in phase 5, the virus has caused sustained community-level outbreaks in at least one other country in another WHO region. This marked the official start of the first global influenza pandemic in 41 years.

The need for an influenza (H1N1) vaccine became clear just months after the first cases were registered. WHO Director-General Dr. Margaret Chan and United Nations Secretary-General Ban Ki-moon met on May 19, 2009 with more than 30 vaccine manufacturers from developing and developed countries. Industry representatives affirmed their cooperation in making vaccine supplies available to developing as well as developed countries, responding to WHO concerns that the pandemic would hit especially hard in low-resource nations. WHO and CDC subsequently provided samples of the seed virus (A/California/7/2009(H1N1)pdm) to pharma companies to use in the development of H1N1 vaccines. On September 15, the FDA approved injectable H1N1 vaccines made by CSL, Novartis and sanofi pasteur as well as an intranasal vaccine made by MedImmune. Regulatory authorities have also licensed pandemic vaccines in Australia, China and the European Union. Many governments are planning mass vaccination campaigns beginning in late September or early October.

Based on preliminary data from adults participating in multiple clinical studies, the four FDA-approved 2009 H1N1 vaccines induce a robust immune response in most healthy adults 8-10 days after a single dose, as occurs with the seasonal influenza vaccine. Ongoing clinical studies will provide additional information about the optimal dose in children. The recommendations for dosing will be updated if indicated by findings from those studies. Potential side effects of the H1N1 vaccines are expected to be similar to those of seasonal flu vaccines.

The following table presents an overview of H1N1 vaccines in late-stage development or approved for marketing. Together these vaccines, which have gone from the stage of conception to market in record time, have been selected as the October 2009 Molecules of the Month.

Information current as of October 1, 2009