Potent mix = ?

Potent mix = the vaccine version of the virus could recombine with the incumbent full-strength strain, and evolve into an even more potent adversary?


Context:

Potent mix?
VIRxSYS is not the first company to successfully test SIV-based vaccines in monkeys. A team led by David Evans of Harvard Medical School in Southborough, Massachusetts, reported successfully protecting monkeys a year ago with a similar "single-cycle" vaccine, this time containing all but one of the SIV genes, but he had no intention of transferring the work to people.

There is still the possibility, however, that in people that already have HIV, the vaccine version of the virus could recombine with the incumbent full-strength strain, and evolve into an even more potent adversary.
Evans thinks VIRxSYS has made this less likely by limiting the vaccine virus to a single cycle of infection. "That certainly makes it safer than a replication-competent live attenuated virus," he says.