Germany and Austria joined the group of nations infected with swine flu after three cases are reported in the former and one in the latter. Canada, New Zealand, Israel, Spain and Britain are on the list of affected nations.
No vaccine is so far discovered to prevent infection. However US health officials aim to have a key ingredient for one ready in early May.
Meanwhile World Health Organisation's (WHO) flu chief, Dr Keiji Fukuda said, "It's a very serious possibility, but it is still too early to say that this is inevitable." On Monday, Apr 27, WHO had raised the pandemic alert level from phase 3 to 4 to reflect the increase in risk of a global outbreak. Level 4 is two places below the top threshold, a full pandemic outbreak.