A single inoculation against AH1N1 flu is not enough, Dutch virologist Ab Osterhaus has warned.

He was responding to research published by Chinese vaccine manufacturers who claim that one inoculation is sufficient. Researchers in the US and Australia support the Chinese view.

In Australia, between 75 and 96 percent of adults were found to be to be adequately protected after just one vaccination, comparable to ordinary flu. Further research must be done to find out how many vaccinations children need.

Dr Osterhaus points out that the Netherlands is using a different kind of vaccine against the so-called Mexican or swine flu, which requires a repeated jab in order to be effective. A nationwide vaccination programme to combat the feared influenza pandemic will begin next month.

Relatively mild
Two people in the Netherlands have died from the flu, out of the 65 who were hospitalised with the disease. Thousands more recovered at home. The AH1N1 flu turns out to be relatively mild, and potentially lethal only to people who are already suffering from other, more serious complaints.

The current incidence is low; according to the latest figures of the Dutch Institute for National Health and the Environment (RIVM), 4.3 out of 10,000 people are afflicted. For the spread to be qualified as an epidemic, at least 6 per 10,000 need to be down with the flu.

Symptoms of (A)H1N1 flu (Wikimedia Commons); Ab Osterhaus (Photo: RNW); A visualisation of H1N1's HA protein (FlickR/Groovelock)