A vaccine is a modified form of natural immunogen which may either be the full pathogen or its components or a toxin. Vaccines prepare and equip your body to defend itself when germs invade it. The purpose of vaccination is to boost the immune system and prevent serious, life-threatening infections.
Immunity to a pathogen can be developed in two ways – by a natural infection or through vaccination. The goal of all vaccines is to trigger an immune response to the antigen so that when the infection strikes in future a stronger immune response will result in a healthy body. Vaccines contain the same antigens found in pathogens, but the exposure is controlled.
Diseases prevented by vaccination
The scope of diseases prevented by vaccination has increased with the introduction of Expanded Program on Immunization (EPI). Vaccination against many diseases is recommended by WHO at the global level. Vaccination against diseases like tuberculosis, polio, diphtheria, tetanus, pertussis, and measles has been followed since the 20th Century.
The other diseases that are now preventable through vaccinations are (since introduction by EPI): hepatitis B, diarrheal disease caused by Rotavirus, pneumonia and other respiratory diseases caused by Hemophilus influenza type B and pneumococcal bacteria. Other vaccines against diseases like yellow fever are recommended in countries where it is prevalent.
Diseases and their associated vaccines are mentioned below:
- Tubercle Bacillus – Bacillus Calmette-Guerin (BCG) vaccine
- Polio Virus – Oral Polio vaccine and Inactivated polio vaccine
- Diphtheria – Diphtheria Toxoid Vaccine
- Tetanus – Tetanus Toxoid Vaccine (TT)
- Pertussis – Whole Cell Pertussis (wP) and Acellular pertussis (aP) vaccine
- Measles virus – measles vaccine
- Measles, mumps, rubella – MMR vaccine
- Hepatitis A virus – Hepatitis A vaccine
- Hepatitis B virus- Hepatitis B Vaccine
- Human Papillomavirus – HPV4 and HPV9
- Rotavirus – Rotavirus vaccine
- Hemophilus Influenzae type B (Hib) – Hib conjugate vaccine
- Pneumococcal infection – Pneumococcal vaccines
- Yellow fever virus – Yellow fever vaccine
- Chickenpox – Varicella vaccine
- Influenza virus – Flu vaccine
- Tetanus, diphtheria, and pertussis – Tdap Vaccine
Adverse reaction after Vaccination
An adverse event following immunization (AEFI) is any untoward medical occurrence that happens after vaccination. This event need not necessarily have a causal relationship with the administration of the vaccine. These adverse reactions may be:
- Product
This is caused or precipitated by a vaccine due to the inherent properties of the product. For example, an extensive swelling of limbs after DTP vaccination. - Quality of the vaccine
This is caused or precipitated by one or more quality defects of the vaccine product. There are times when the manufacturer fails to completely deactivate a lot of inactivated polio vaccine which may lead to paralytic polio. - Immunization error
This can be caused by inappropriate handling, prescribing or administering a particular vaccine. For example transmission of an infection through a multidose vial. - Coincidental reaction
This is caused by other reasons (apart from above). Coincidental occurrences due to other health issues are examples of such AEFI.
Regulatory authorities must ensure that all vaccine components, either single or in combination, do not violate safety standards.
Method of administration of vaccines
Different vaccines have to be administered in different ways in order to be effective and not cause Adverse Event Following Immunization, AEFI.
- Oral administration- OPV and Rotavirus
- Intramuscular- Hepatitis B, IPV, Hib, PCV-7, DTwP, DTaP, Td, and TT
- Subcutaneous Measles and yellow fever
- Intradermal- BCG
