Just 45 days earlier, WHO had raised the pandemic level for influenzas to phase 4, with the arrival and spread of a new H1N1 virus. Believed to have originated in pigs, it spread from Mexico to the US and all corners of the globe. American health authorities sounded the alarm when some students developed flu-like symptoms and tested positive for Swine flu, after a Mexico holiday.

As the numbers of the infected grew rapidly, WHO watched with concern. From the 16th century, every century has experienced approximately three influenza pandemics, occurring at intervals of between ten to 50 years. Since the last one occurred in 1968-69, by this count the next pandemic was long overdue.

The three outbreaks of the 20th century killed between 60- 80 million people. The Spanish Flu of 1918-1919 saw a lethal form that caused viral pneumonia with extensive hemorrhaging of the lungs that could kill a perfectly fit person within 48 hours. Within a few months the virus had spread to every part of the world, killing over 40-50 million. The next two pandemics occurred in 1957-58 and in 1968-69.

The 2003 SAARS outbreak demonstrated that new infections can cross conti nents in a matter of days. A severe infection today would spread rapidly and strike millions.

This new H1N1 virus is a combination of three viruses, human, avian and swine and WHO now refers to it as (A) H1N1 virus.

While the majority of cases have suffered a mild form of infection, about two per cent have developed severe pneumonias and infection. This virus is attacking the healthy, young-middle-age group, mainly between ages 30 and 50, reminiscent of the Spanish Flu. Also, past pandemics have seen several waves of infection, with a mild first wave, followed within a few months with a second more virulent form.

For the past five years, the global health community had been watching for signs of an impending outbreak of a new influenza strain. The most likely candidate was considered to be the H5N1 strain of Avian influenza or bird flu - that infected wild and domestic ducks and poultry. That virus had already jumped the species barrier, infecting human beings in several countries. But though widespread, the H5N1 virus was less efficient in infecting humans. Since 2004, it has infected 421 people, killing 257 or 61%. Strict watch was being kept on countries with a wide circulation of the virus, in case reassortment or mixing, with human influenza caused H5N1 to mutate further into a more virulent form.

Simultaneously, the world prepared to tackle a pandemic outbreak. International and national agencies across sectors made detailed action plans for joint response to a pandemic.

WHO's table of phases denoting different levels of a possible pandemic was till April 23 at phase 3 for the then known H5N1 Avian virus. This level indicates that there has been transmission of an animal or humananimal influenza reassortant virus causing sporadic, individual cases, but without sustained human to human transmission.

Between April and June, as cases of H1N1 were reported from across the world, the alert was rapidly raised from 4, to 5 and then 6. As per the International Health Regulations to which all countries are signatories, countries are expected to notify WHO about any new cases of H1N1 within 24 hours.

By June the growing concern was that the reported cases were small and mainly those detected by countries with a high standard of surveillance. The real numbers could be much higher, many remaining undetected, in countries with weaker health infrastructures. According to WHO, further spread of the infection is inevitable

Should people in India be concerned about the spread of H1N1? How can they protect themselves?

Every year, seasonal influenza kills 250,000 to 500,000 people worldwide. In temperate countries of the Northern hemisphere, the vulnerable age groups, the very young and the elderly, are routinely vaccinated against the circulating influenza strain. In tropical countries, including India, people don't consider seasonal influenza as a serious illness. Actually, even tropical countries face up to three cycles of seasonal flu outbreaks annually and yes, the new H1N1 influenza must be taken seriously.

The H1N1 is being watched carefully for possible mutation. According to the WHO Director General, we are far better prepared to deal with a pandemic today. Dr Chang said, "The world can now reap the benefits of investments, over the last five years, in pandemic preparedness."

Countries have now activated their pandemic plans, and existing networks of expertise in influenzas, laboratories and pharmaceuticals. Most countries, including India, have instituted safeguards at national entry points and any suspected infected persons are being isolated, tested and treated.

What are the symptoms of infection? Early signs of influenza A (H1N1) are flu-like, including fever, cough, headache, muscle and joint pain, sore throat and runny nose, and sometimes vomiting or diarrhoea.

Now that the disease is at the pandemic stage, people are advised to follow public- health advice regarding school closures, avoid crowds and observe other social distancing measures in cities where infections have been reported.

Are there medicines to treat a person with H1N1? Yes most governments have a stockpile of the drugs including oseltamivir (Tamiflu). While over- thecounter sales are prohibited to prevent self-medication and the possibility of the virus developing drug resistance, government hospitals have a ready supply.

Presently, there is no vaccine although there is a growing demand for it. Work has commenced and pharmaceutical companies, including Indian companies, are bidding for its production. Making a new vaccine could take up to 6 months.

As we watch the infection spread, it is also time for humans to seriously review current practices of industrial livestock farming. In most countries, given rapid urbanization and huge increase in meat consumption, commercial pig and poultry farms are increasingly situated closer to crowded, urban habitations. Commercial needs dictate manipulation, including genetic manipulation in rearing these animals. Pumped with antibiotics and hormones to speed maturation, when these animals fall ill, the disease spreads very fast among them. Will this produce a super virus and trigger a virulent human pandemic? Unless we improve our livestock rearing practices, this is the next tragedy waiting to happen.

Whether H1N1 will prove to become more virulent in its second wave remains to be seen, but vigilance will have to be maintained for several months, in both hemispheres. Experience in handling this pandemic will test the preparedness plans and provide lessons for improvement. Eventually, planning and preparedness are the best tools to contain and control any outbreaks- this or the next one.

Updated information on H1N1 is available at the WHO website: www.who.int and the CDC website: www.cdc.org. A site called HealthMap visually depicts the geographic spread of the virus, and there are several Twitter and blog sites providing ongoing information.