My daughter & I both reacted to the first dose with headache, backache, fever and nausea, but my husband just had a sore arm. My daughter's reaction to the second was quite pronounced - flu-like symptoms and fever for 2 days - of course, she had Covid back in March, so probably was mounting a BIG immune response to the vaccine. My other daughter got the Moderna vaccine, and she got "Covid Arm" - swollen bicep and lymph glands, fever and nausea - a week after the first dose - also sign of a proper immune response, felt by a fair number (but by no means the majority) of injectees.
We are all different - your results may vary.
Sue