The announcement is a boost for a generation of Thai health workers who have transformed the nation from one of Asia's most HIV-ravaged societies to a pin-up for how to effectively tackle the crisis.
    
Describing the elimination as a "remarkable achievement", the WHO said Thailand was "the first (country) with a large HIV epidemic to ensure an AIDS-free generation."
    
Belarus and Armenia were also declared free of mother-to-baby HIV transmissions today but both nations have a much lower prevalence of the virus.
    
Previously Cuba was the only other country to have eliminated mother-to-child transmission under the WHO's criteria back in July 2015.
    
The global health body said Thailand's routine screening and universal free medication for pregnant women with HIV was crucial in stopping the virus being passed to new generations.
    
If left untreated, mothers with HIV have a 15-45 percent chance of transmitting the virus to their children during pregnancy, childbirth or while breastfeeding.
    
But taking antiretroviral drugs during pregnancy significantly reduces those chances to just over one percent. In 2000 Thailand became one of the first countries in the world to provide free antiretroviral medication to all pregnant women diagnosed with HIV.
    
Screening for the virus during pregnancy is also routine, even in the country's most remote areas, the WHO added. According to Thai government figures, the number of babies born with HIV has dropped from 1,000 in 2000 to just 85 last year, a large enough fall for the WHO to declare mother-to-child transmission over.
    
A small number of cases are taken into account, as treatment with medicine is not 100 percent effective. It is a major turnaround for Thailand. The country went from 100,000 HIV cases in 1990 to more than a million three years later, fuelled in part by its huge sex trade. Health workers initially struggled to persuade governments to act.

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