The findings were announced at the WHO's annual assembly in Geneva, which drew health chiefs from around the globe who were screened for SARS symptoms by rubber-gloved nurses in lab coats before meetings got under way Monday.
The results could be welcome news for the world's air carriers, which have suffered a deep slump in traffic, especially in Asia, while the disease spread to more than two dozen countries and killed at least 643 since it first surfaced in southern China in November.
WHO's global coordinator for anti-SARS efforts, Mike Ryan, said airport screening of passengers for fevers and other symptoms has drastically reduced the danger of contracting SARS while on a plane.
"The phenomenon of airline transmission of SARS is historical now, we believe," Ryan said.
"Of course, there is always a risk if a SARS patient gets on a plane, but the idea is to prevent them from getting on the plane in the first place and the risk, we believe, has been reduced now to infinitesimally low levels because of screening and surveillance," he added.
WHO Director-General Dr. Gro Harlem Brundtland appealed to governments worldwide to work closer together in the fight against SARS.
"It has never been clearer than today that a secure, healthy future for us all depends on cooperation across borders and between institutions," Brundtland told the opening session of the 10-day meeting. "We can no longer rely on national efforts alone to implement the scaled up system of global alert and response that the world now needs."
The International Air Transport Association says SARS has caused more damage to the global airline industry than the Sept. 11 attacks and the war in Iraq combined, and that the air industry expects a loss of US$10 billion this year.
Nowhere has the tourism industry been hurt more than in Asia, even in nations where the threat is relatively small.
Thailand's government decided Monday to buy insurance coverage for foreign tourists that would pay US$100,000 apiece if they die from SARS contracted while visiting Thailand. Thailand has reported just two deaths from SARS, both people who acquired the disease abroad.
In another effort to boost travel, China is reducing landing fees by 20 percent, the International Air Transport Association said Monday, adding that several other countries have already done the same.
At the Geneva meeting, WHO medical experts said that all of the 16 cases of people contracting SARS while aboard a plane happened on a total of four flights and before before airlines adopted tough screening measures.
"There were 35 flights on which SARS-infected people who were symptomatic with disease traveled," said Dr. David Heymann, WHO's chief of communicable diseases. "We know, however, that on only four of those planes was there actually passage of the disease."
Of those, 14 were passengers sitting within four seats of the SARS patient and two were flight attendants, Ryan said.
"Proximity is a huge part of this picture. The vast majority have been within two rows in front or two rows behind. Not sharing toilets, not walking up and down the aisle, not sitting in the waiting area — none of those issues seem to be associated," Ryan said.
All 16 cases occurred before March 23, four days before the U.N. health agency recommended that airlines screen passengers for signs of SARS and advised that suspected cases not be allowed to travel. SARS is not contagious unless symptoms are showing, experts say.