A mild side-effect with a COVID shot is an immune reaction that causes low levels of inflammation in the body, mostly causing reactions nearby to the site of injection. Mild side-effects include running a fever, pain at the injection site, body pain, weakness and chills.
Compared to this, an adverse reaction to the COVID-19 vaccine is termed to be the one that has the potential to cause serious damage, may often be resultant of an autoimmune flare-up and impact vital organs as well. Adverse reactions are considered to be an ‘undesirable’ side-effect and can be local, systematic or allergic in nature.
While milder intensity reactogenic side-effects tend to resolve in a span of 2-3 days, severe, adverse reactions can come up a while later, and take a longer time to resolve, along with the need for a clinical check-up as well.