Mutant strains lacking pili show severely attenuated pathogenicity. There are both attenuated vaccines and inactivated vaccines available. Several other vaccine candidates in development including live attenuated, inactivated, DNA and subunit vaccines. Rubella infections are prevented by active immunisation programs using live attenuated virus vaccines. Lower energy photons are attenuated preferentially by differing absorber materials. Astrogliosis may also be attenuated by inhibiting the microgliosis response. As different LORs must traverse different thicknesses of tissue, the photons are attenuated differentially. Using an attenuated virus, Hextall identifies a potential vaccine. Some vaccines contain live, attenuated microorganisms. Although most attenuated vaccines are viral, some are bacterial in nature. Attenuated vaccines have some advantages and disadvantages. Signals are either heavily attenuated by the building materials or reflected as in multipath. Shorter wavelengths are useful for smaller particles, but the signal is more quickly attenuated. The signal is naturally attenuated but modern sonar suites are very sensitive. Furthermore, the signal is attenuated by the medium the beam crosses, and the beam disperses.