As its name implies, the blood brain barrier protects the brain from whatever happens to flow in the blood stream. The herpes virus enters the brain by another channel : the peripheral, somatosensory nerve cells whose axon has a T shape. One prong of the top bar goes to the peripheral tissue, and the other prong goes up to the brainstem.
Expanding further: the blood brain barrier is made of cytoplasmic expansions of astrocytes in the central nervous system. The T-shape sensory cells are part of the peripheral nervous system, their axon ends up in the encephalon.