The vast majority of cases of pandemic influenza A (H1N1) have been mild so far with few deaths. It remains to be seen whether the virus will mutate into a more virulent strain. Marie-Paule Kieny explains how WHO is supporting countries' efforts to protect their populations with vaccines that should become available as of this month. Q: When will the first doses of vaccine for the pandemic influenza A (H1N1) be ready? A: Some manufacturers announced in July that vaccine is available, but that doesn't mean it's ready for use, as it needs regulatory approval. Regulatory authorities are considering the best way to register these vaccines as quickly as possible. The consensus is that the first doses will be available to governments for use in September. Q: Who will get vaccinated first? Who decides this? A: Vaccine will not be available on the private market and governments will decide who gets vaccinated first. WHO recommends that health workers be the first, to protect the health system and allow them to care for influenza and other patients. The strategy a country takes will depend on its policy objectives and the availability of vaccine. For example, if a country decides to concentrate on protecting essential infrastructure, it may target different people, such as truck drivers, if they are critical for food delivery. Others may try to reduce transmission of the virus. For example, the United States of America decided to immunize children before or at school entry who are in closer physical contact than adults and can amplify infection rates. Countries may also try to reduce morbidity and mortality and target specific groups, such as pregnant women. Some high-income countries have ordered enough vaccine for the whole population. Nevertheless, no countries will have vaccine for everyone from the first day it is available for use, so that each country will need to prioritize. Some middle-income countries have also placed contracts with pharmaceutical companies and have been purchasing vaccine for between 1% and 10-20% of the population. WHO is working hard with manufacturers, governments and donors to ensure that developing countries can access vaccine as soon as possible to immunize their health workers, and when more vaccine becomes available, other groups will be immunized. Q: How are influenza vaccines produced? A: The main method is by injecting seed virus into embryonic chicken eggs and harvesting the fluid after several days and purifying it. There are two technologies. More than 90% of influenza vaccines available are known as vaccines, which means you kill the virus to produce the vaccine. Less common are attenuated vaccines, which are derived from a weakened form of the virus that is not killed. Q: How many different vaccine candidates will be available for A (H1N1)? A: About 30. Most will be inactivated virus vaccines made in eggs, some will be killed virus vaccines made in cell cultures and a few will be live attenuated virus vaccines. Then you have a lot of variation in the way vaccine is purified and in whether or not it is mixed with an additive, called an adjuvant, which is a booster of immunogenicity (which is the capacity of a vaccine to evoke an immune response) and which is used with killed virus vaccine. All vaccines create antibodies to fight the virus; some will produce a local response, such as attenuated vaccine administered in the nose to give more immunity at the port of entry of the virus. The industry will use tiered pricing, so high-income countries might pay between US$10-20 per dose, middle-income countries may pay about half that and low-income half that price again. These are ballpark figures but this is the order of magnitude. Q: Isn't it too early to produce vaccines because the pandemic virus could mutate? A: Although the virus can mutate, we hope that there will be enough cross-protection through recognition of the new virus. …