COVID-19 vaccination activates antibodies targeting parts of virus spike protein shared between coronaviruses

'Our theory is that there is actually memory from previous common cold coronavirus encounters, and when you get the vaccine for SARS-CoV-2, the vaccine reawakens some of those memories. Then you see this early response which is basically just a rapid memory response to what you've already seen,' Altin said. 'With time, the immune system can reshape those responses more in the direction of the pandemic virus.'