Russia's consumer rights regulator said on Tuesday that the number of confirmed human swine flu cases has risen to 163,800 worldwide with 998 deaths, according to the RiaNovosti.

The novel H1N1 swine flu is now so widespread that the World Health Organization has stopped counting individual cases.

Health experts are afraid it could worsen, especially when the Northern Hemisphere's influenza season starts in the autumn.

Flu vaccines are made using an old-fashioned method -- inoculating eggs with the virus, letting it grow, and then purifying and inactivating it to make the vaccine.

H1N1 not only hits those with chronic diseases particularly hard but also, unusually, young adults and older schoolchildren.

Vaccine makers and academic centers are racing to test H1N1 vaccines in volunteers and in various doses to see what is safe and what dose is likely to best protect people.

Some European countries have also suggested they may start vaccination campaigns before full results are available from these trials.