The World Health Organization predicts the H1N1 Swine Flu virus will infect two billion people, or one out of every three persons, over the next two years.  While this flu has already killed 800, the WHO says thousands more could die unless an effective vaccine is developed soon.  

This year's pandemic spread around the globe with record-breaking speed.  It has taken less than two months for the H1N1 swine flu to spread, while previous pandemics took six months or longer.  

Yet Dr. Keiji Fukuda of the World Health Organization warns this global outbreak is still in the early stages.  "We have a very large global population, and it is quite clear that we'll continue to see spread of this virus through countries, and then among countries," he said.

Most of the patients have been teenagers, between 12 and 17 years old.  But the virus is spreading more deeply into many communities and the WHO says the average age of patients now appears to be getting slightly older.  

While young people and pregnant women are still at higher risk for contracting the H1N1 virus, health officials also caution that patients with cardiovascular disease, respiratory illness, diabetes, cancer, and obesity are just as vulnerable.

Some clinical trials of potential vaccines are underway, others will start soon.  

The European Medicines Agency says large scale clinical trials will be bypassed in order to get vaccines into the general population as soon as possible.  

Health officials in Britain, Greece, France and Sweden have announced they will begin inoculations among the public possibly within weeks.  

The WHO's Dr. Fukuda has not criticized that decision, but expressed concern about rushing vaccine production too soon. "There are certain things which cannot be compromised," he explains. "And one of the things which cannot be compromised is the safety of vaccines. There can't be any questions whether the vaccine is safe or not."

Meanwhile, the World Health Organization says countries with widespread infections have switched from reporting individual testing of all patients, to monitoring and reporting trends in the population.  

According to the WHO, testing of patients has strained the laboratory capacity of many countries.  

Dr. Fukuda believes health officials can still accurately predict the pandemic's size. "We know that the total number of laboratory confirmed cases is really only a subset of the total number of cases," he asserts. 

Recently, the international health organization said it would no longer publish global tables reporting the number of new cases for all countries.