A significant trend was found across age groups for local side effects from dose 1 ( P < 0.01) where the 20- to 29-year-old and 30- to 39-year-old groups tended to report more side effects than other age groups ( Fig. 5D ).
We found that recovered individuals reported more systemic side effects after receiving their first dose of the vaccine than naive individuals did and although these results did not reach statistical significance, several other studies have found a similar pattern ( 23 , 25 , 26 , 38 , 39 ).