Significant redness, soreness, and swelling are common for the first 2-3 days after immunization. You may even be able to feel a hard lump at the injection site and that can actually last 3-4 weeks... If at any time you think there's a chance of infection (pus draining, red streaks radiating from the site, or feels really hot and hard to the touch after 3-4 days that appears to be getting worse instead of better) then you need to see your Dr.