Human trial of H5N1 vaccine could be dangerous?

According to this report Vietnam is getting ready to test a new vaccine for H5N1 avian flu this summer. However, some are concerned about the methods used to develop this vaccine:

The seed virus used for Vietnam's vaccine was mixed with cancer cells to boost replication, and then grown in monkey kidney cells, a method the article describes as highly unorthodox. It is not the same seed virus as the one approved by the World Health Organization (WHO) for H5N1 vaccine development.

"People could get cancer from the vaccine," according to a TIME quote attributed to Klaus Stohr, head of the WHO's global influenza program.

ahumadameister.