Both of these things are true.
Years before I was born, back in the 60s, they developed an RSV vaccine and human trials went horrifically wrong. Kids who were in the human trial not only did not avoid RSV, they were vastly more likely to be hospitalized. More than one child died. So of course this put scientists off the idea of another vaccine for decades.
Now, however, things are dire enough to renew interest in an RSV vaccine and there’s at least one candidate in trials.