The scientist credited with having co-discovered the virus that causes AIDS told a European conference in Hamburg he believed a proper vaccine was still a long way off.
"The search is proving more and more difficult because the HIV virus is changing all the time," French researcher Luc Montagnier told the conference on the disease Sunday, adding he thought no vaccine likely for some years yet.
He said many pharmaceutical companies already had canceled programs to develop an HIV vaccine.
Montagnier told delegates that while some animals had been made resistant to HIV in tests, applying this to humans was proving difficult and involved separate medical risks. Nonetheless, he said he was optimistic that significant progress in the treatment of humans was likely within five to 10 years.
Doctors who have volunteered to inject themselves to test an experimental vaccine were warned earlier this month they ran serious risk of catching the disease.