Early results from clinical trials show that the majority of healthy adults may only need one vaccine shot rather than two to protect against the H1N1 virus. Results are showing that the effects of the vaccine are starting faster than expected. Those results could mean that the limited vaccine supply, with an estimated 45 million doses to be made available next month because of poorer-than-expected yields from growing the virus in chicken eggs, could be stretched further if only one shot is needed. The clinical study is being conducted by Australian firm CSL Ltd. and the National Institute of Allergy and Infectious Diseases.