Worldwide, most infected patients continue to display typical influenza symptoms and fully recover within a week without any form of medical treatment, the WHO said.
According to the new guidelines, formed by consensus by a global group of experts, patients with uncomplicated illnesses do not need to be treated with antiviral medicines.
The guidelines emphasise using drugs such as oseltamivir and zanamivir, to which the pandemic virus is susceptible, to prevent severe illness and deaths, reduce the need for hospitalisation, and shorten hospital stays.
When properly prescribed, oseltamivir is found to significantly curb the risk of pneumonia, a leading cause of death for both the pandemic and seasonal influenza, it said.
WHO recommends treatment with the drug as soon as possible among people who are severely or whose conditions begin to deteriorate.
Where oseltamivir is not available, zanamivir can be given. The virus is currently resistant to a second class of antiviral, known as M2 inhibitors.
As pregnant women are among the groups considered being at increased risk, WHO recommends that they receive antiviral treatment as soon as possible after the onset of symptoms.
The guidelines call for prompt treatment for children including those under five years of age with severe or worsening illnesses, as well as those at risk of more severe or complicated illness.
Otherwise healthy children over five years, WHO said, do not need antiviral treatment unless their conditions persist or worsen.
If someone with confirmed or suspected H1N1 infections shows symptoms including shortness of breath, chest pain and high fever lasting beyond three days, they should seek immediate medical attention.
Among children, warning signs include fast or difficult breathing, lack of alertness, difficulty in waking up and little or no desire to play.
Image: Girls wearing masks at a station in Tokyo
Photograph: Kim Kyung-Hoon / Reuters