The answer is in the picture
This may be a sebaceous cyst. This type of bump develops when sebaceous glands are blocked. Sebum builds up and a bump develops. This bump can feel hard to touch. Sebum is naturally produced, so there usually is not inflammation.
The vaccines that are required by law, according to the Childhood Vaccine Injury Act of 1986 are:
1. Diptheria, Pertussis and Tetanus Vaccine (DTP, DTap, DT, TT or Td)
2. Measles, Mumps and Rubella Vaccine (MMR)
3. Chickenpox Vaccine (Varicella)
4. Rotavirus and Pneumococcal Conjugate Vaccines
5. Haemophilus Influenzae type b Vaccine (Hib)