If you're really that surprised by this, then you might want to look into topics like Original Antigenic Sin and vaccine-enhanced disease, especially antibody-d

If you're really that surprised by this, then you might want to look into topics like Original Antigenic Sin and vaccine-enhanced disease, especially antibody-dependant enhancement, which is the reason that previous vaccine candidates for coronaviruses (which would be a huge market, given how many old people have died from them each year, historically) haven't progressed beyond animal trials.