An alien race advance enough to space travel and make energy weapon must also know basic facts of microbiologyIt kills some people who develop allergic reaction but it is beneficial to mankind as a whole.
“By the toll of a billion deaths man has bought his birthright of the earth, and it is his against all comers; it would still be his were the Martians ten times as mighty as they are. For neither do men live nor die in vain.”
― H.G. Wells, The War of the Worlds
And would have developed adicate biosafety measures