Combination of a lot of factors, vaccine research was still fairly new and virology wasn't nearly as well understood as it is now. They were targeting the wrong proteins and getting frustrated that they weren't getting the results they expected. Come to find out, RSV actually changes shape (protein unfolding) after it enters the cell. This is important because antibodies can only prevent a cell from getting infected, antibodies cannot enter a cell and push the virus out. So researchers were taking infected cells, analyzing the virus in those cells (after it changed shape) and tried to make a vaccine that would teach the immune system target those structures. But those structures weren't found outside the cell, and the immune response was hindered because of that.

Luckily, someone figured that out, and they redirected their focus and were able to create a vaccine that teaches the immune system to target the virus structure before it enters the cell and now RSV vaccines actually work the way they should.

https://www.nature.com/articles/d41586-021-03704-y#:~:text=Tragically%2C%20the%20shot%20did%20the,the%20trial%20and%20killed%20two.

I thought I was in the r/Hermitcraft subreddit and this was a reference to Scar.

Depends on how close the are to that star that went boom. It might be VERY bright.