Keiji Fukuda, WHO's Assistant Director-General for Health Security and Environment, told The Associated Press on Friday that previous pandemics show even a few million cases could be "relatively early in the pandemic" and that given the size of the world's population, the new H1N1 virus is likely to spread for some time.
Fukuda says reports from Britain of a sharp spike in cases is consistent with WHO's expectations even though the Geneva-based agency has only received confirmed reports of some 130,000 infections worldwide.
The global health agency stopped asking governments to report new cases last week, saying the effort was too great now that the disease has become so widespread in some countries.
Health authorities in Britain say there were over 100,000 infections in England alone last week, while U.S. authorities estimate the United States has over 1 million swine flu cases. Those figures dwarf WHO's tally of 130,000 confirmed cases worldwide since the start of the outbreak last spring.
"We know that the total number of laboratory confirmed cases is really only a subset of the total number of cases," Fukuda said.
Fukuda, the former chief of epidemiology at the U.S. Centers for Disease Control and Prevention, also said there must be no doubt over the safety of swine flu vaccines before they are given to the public.
Health officials and drug makers are looking into ways of speeding up the production of the vaccine before the northern hemisphere enters its flu season in the fall.
"Everybody involved with the vaccine work, from manufacturers up to the regulatory agencies, are looking at what steps can be taken to make the process as streamlined as possible," Fukuda said. "One of the things which cannot be compromised is the safety of vaccines."