"We must take our fight against Aids to a much higher level," the deputy president, Phumzile Mlambo-Ngcuka, told a conference of Aids activists, who until recently had been ignored and even denounced by the government. "We must tighten up so that ARV [antiretroviral] drugs are more accessible, especially to the poor. Education and prevention of HIV infection must be scaled up. Our people want us to unite on this issue in the best interests of the health and wellbeing of our nation. Working together we can defeat this disease," she said to cheers from a crowd of health professionals, church leaders and labour officials.

Experts said the government's policy change could save thousands of lives. An estimated 5.4 million of South Africa's 47 million people are infected with HIV, one of the highest ratios in the world. "This is a sea change," said Mark Heywood, director of the Aids Law Project. "We're not across the ocean yet, but now the government is sailing in the right direction."

Activists fought a prolonged legal battle that forced president Thabo Mbeki's government to distribute the life-saving ARV drugs through the public health services. "The government is finally acknowledging that Aids is a serious national problem and is taking a scientific approach to tackling it. It's long overdue, but it is worth celebrating," said a senior doctor working in a government hospital.

Mr Mbeki had questioned that Aids was caused by HIV and said it was not certain that ARV drugs were safe and effective. He denied knowing anyone who had died of Aids, despite several prominent South Africans succumbing.

After a 2003 court ruling, the government reluctantly rolled out a public programme to make ARV drugs available to people with Aids. About 200,000 people receive the government drugs, making the public programme one of the biggest in the world. But they are reaching just one quarter of the estimated 800,000 in need.

Confusion over what is effective Aids treatment was spread by the health minister, Manto Tshabalala-Msimang, who adamantly promoted a diet of beetroot, lemons and garlic as an alternative treatment. At the Toronto Aids conference in August, she sparked an uproar with a South African government display of the fruits and vegetables but no ARV drugs. The South African government's position on Aids was denounced as "wrong, immoral and indefensible" by theUN's top official on Aids, Stephen Lewis. President Mbeki has been silent on Aids issues recently and has not sacked Ms Tshabalala-Msimang as demanded by international and domestic Aids campaigners. But significantly, the president marginalised the health minister by making his deputy president the head of an Aids taskforce and it appears he authorised her to change government policies.

In recent weeks the soft-spoken but savvy Phumzile Mlambo-Ngcuka had signalled the change by meeting privately with Aids specialists whom the government had previously refused to consult. She has accepted that Aids is caused by HIV and emphasised that ARV drugs are central to fighting the disease.

A month ago, Aids activist Zackie Achmat and 40 members of the Treatment Action Campaign were arrested for demonstrating in government offices for the sacking of Ms Tshabalala-Msimang. Yesterday Mr Achmat, in his trademark "HIV Positive" T-shirt, walked arm in arm with the deputy president and was kissed and hugged by other top officials. "This is a serious, significant change. The government wants to work with us, not against us," he said. "By increasing the availability of drugs, particularly for preventing mother to child transmission, the government is going to save lives."