The world is highly vulnerable to a severe flu pandemic and governments should increase surveillance, vigilance and preparedness, the World Health Organization (WHO) has said.
"Nothing about influenza is predictable - including where the next pandemic might emerge and which virus might be responsible," the United Nations health agency warned while noting the next pandemic could be worse than the 2009 swine flu outbreak that killed over 284,000.
This year's seasonal flu season has been bad in many parts of the world, with Asia, the Americas and Europe reporting high levels of circulating flu viruses and low levels of protection from vaccines that did not match the relevant strains.
The health organisation is particularly concerned about avian influenza noting that the diversity and geographical distribution of influenza viruses currently circulating in wild and domestic birds are unprecedented.
"The world needs to be concerned," it said.
The highly pathogenic H5N1 avian influenza virus, which has been causing poultry outbreaks in Asia almost continuously since 2003 and is now endemic in several countries, is the influenza virus of greatest concern for human health.
Over the past two years, H5N1 has been joined by newly detected H5N2, H5N3, H5N6, and H5N8 strains, all of which are currently circulating in different parts of the world.
Praising virological research that had increased capability to detect, understand and assess new viruses for pandemic risk, and to track their international spread, the WHO noted that this has to be stepped up.
More antiviral medicines, including peramivir and laninamivir as well as oseltamivir and zanamivir, are now available to treat influenza and reduce the duration and severity of infection.
But better vaccines and shorter production times are required. More people would die in the three to four months currently needed to manufacture vaccines.
Swine flu toll in India
The WHO has said it is "carefully watching" the current swine flu outbreak in India.
The toll in two months has crossed 1,041 with cases breaching the 19,000 mark by Saturday, 28 February.
Many parts of India including Mumbai are facing a shortage of laboratories for testing swine flu and isolation units.
While the government has said that government hospitals are equipped for tests, in many cities people are being sent away to private labs charging a whopping £50 (Rs 5,000) for the test.