In Europe, there were at least 16,556 instances of the virus in humans and 34 deaths.

The Eastern Mediterranean area had one death and Africa has so far had none confirmed.

The tally, posted to the UN health agency's website, contained a disclaimer: 'Given that countries are no longer required to test and report individual cases, the number of cases reported actually understates the real number of cases.'

While many cases are thought to be so mild that they are not reported, the WHO has urged vigilance, saying the nature of a virus could change.

Swine flu is susceptible to anti-virals. A vaccine is expected to be ready in the autumn.