SHANGHAI - No evidence has been found showing the H7N9 avian flu strain can be transmitted through human-to-human contacts, a panel of Chinese and World Health Organization (WHO) experts said on Monday.

However, the experts said they need to run more tests.

"Our knowledge of H7N9 bird flu is very limited right now. We must do more sensitive and more extensive monitoring to determine the origins and variations of the virus," said Yang Weizhong, deputy director with the Chinese Center for Disease Control and Prevention. Yang is co-head of the expert panel.

The panel believes it is not yet the time to make vaccines for the new type of bird flu that has killed 21 people in China.

"We will continue to ask ourself over and over again but right now there is no need to do that," said WHO Assistant Secretary-General Keiji Fukuda.

The experts said Shanghai has been open and transparent to the panel's investigation, and the government's responses to H7N9 avian flu have been timely and effective.