Introduction to Vaccine schedule:
When administering vaccines, a variety of aspects should be taken into account, including the scheduling of each dosage, screening for precautions and contraindications, the number of doses to be given, the patients’ and parents’ educational needs, and how to interpret and handle adverse effects. Additionally, the recipient’s age, immunological condition, and vaccine type all play a role.
Unconjugated polysaccharide vaccines do not induce T-cell memory, and additional doses might increase the duration of protection. Even while antibody titers gradually decrease, vaccinations that promote both cell-mediated immunity and humoral (such as live attenuated viral vaccines) can typically produce sustained immunity.
Key Considerations in Vaccine Scheduling:
- Optimal protection is ensured when multidose vaccines are administered precisely at the recommended ages and intervals. For example, in the case of the hepatitis A vaccine, if the two doses are administered with less than a six-month gap, the second dose is deemed ineffective and must be repeated six months after the initial dose.
- Doses given up to four days earlier than the minimum required age or interval are still considered valid, as part of a “grace period”.
- However, if the first dose is administered five or more days before the child reaches the recommended minimum age, that dose is considered invalid. It must be repeated once the child meets the minimum age requirement. For live vaccines, a repeat dose should only be given after at least 28 days have passed since the improperly timed dose.
- Simultaneous vaccine administration involves giving more than one vaccine during the same healthcare visit, using different injection sites and separate syringes. This method is typically advised for children who do not have any medical conditions that would prevent vaccination. Administering all necessary vaccines during one visit ensures timely protection and increases vaccination rates. For instance, the efficacy of the varicella and MMR (measles, mumps, rubella) vaccines can be maintained if administered concurrently. Similarly, when given in combination, the live attenuated influenza vaccine (LAIV) has no effect on the immunological response to either varicella or MMR. However, this practice isn’t universally applicable. In people with specific health conditions—such as those with HIV infection or who lack a spleen—it’s advised not to give the quadrivalent meningococcal conjugate vaccine (MCV4-D/Menactra) and the pneumococcal conjugate vaccine (PCV13/Prevnar 13) during the same visit.
- Combination vaccines merge components from multiple vaccines into one shot. These are designed either to protect against several strains of a single disease-causing organism or to prevent multiple diseases, thereby reducing the number of injections a person needs. Combination vaccines may have the following benefits: higher vaccination rates, prompt vaccination coverage for children who are behind schedule, lower shipping and stocking costs, lower costs for additional medical visits required due to vaccination deferral, and easier integration of new vaccines into immunization programs.
- One potential disadvantage of combination vaccines is an increased likelihood of side effects. For example, the MMRV (measles, mumps, rubella, varicella) combination vaccine has been associated with a higher risk of fever and related reactions compared to when the individual MMR and varicella vaccines are given separately during the same visit.
- There is no proof that inactivated vaccines affect how the body reacts to live or other inactivated immunizations. It is possible to administer two doses of any inactivated vaccine simultaneously. There are two exceptions: MenACWY-D and PCV13 were separated by one week in an individual with anatomic asplenia. If a live-virus vaccine is given within 28 days (four weeks) of another live-virus vaccine, the immune response to the first one may be compromised. This 4-week gap between two distinct live vaccinations shouldn’t be covered by the 4-day grace period.
Quality control in vaccine:
To guarantee that manufactured vaccinations are safe, effective, and of a constant caliber, quality control is carried out. To guarantee the safety and effectiveness of the vaccines, in addition to advance testing, vaccination rules require a number of tactics, such as cell banking, seed lot systems, supplier audits, master seeds, adherence to good manufacturing practices,
improved pre- and post-marketing surveillance to search for potential adverse effects after immunization (AEFI) and independent lot release from the National Regulatory Authority.
The vast experience in the sector, which includes post-marketing monitoring of side effects and case reduction, determines the effectiveness and safety of vaccinations.
Tests for quality characterization of vaccines:
Characterization of starting materials
This ensures that production system must be based on well characterized master and working cell bank system like knowledge of viability during storage, genealogy, genetic markers, tumorigenicity, absence of detectable contaminants etc.
Increase in virulence test
With live vaccines, there is concern of organism being shed from host and could be of potential risk to environment. All live vaccines should be tested for virulence by means of passage studies.
Interference test
For vaccines which contain two or more antigenic components, tests
should be confirmed to ensure no interference between individual components.
Stability test
It is performed to establish validity of expiry date that appears on the product package
Validation of production process: Regular, periodic validation that manufactured product is safe potent and each batch is of equally high quality is another major function of assuring the quality and safety of vaccine.
Proof of consistency in production
Prior to marketing approval of vaccine, each establishment should produce three consecutive production batches of completed product to evaluate product consistency. Validation process has proved to demonstrate a high level of assurance of batch-to-batch reproducibility and they conform to all the criteria of National Regulatory Agencies (NRA). Hence NRA will officially certify the finished product.
Independent lot release
WHO insists on the formation of NRA in every country for independent lot release of every batch of every vaccine being manufactured in that country. This proves to be one of the key elements in
assurance of vaccine quality. This lot release process provides a major check on manufacturer’s
performance in controlling lot release by the NRA and is a key to the control of vaccines.
References:
- Centers for Disease Control and Prevention. (2011). General recommendations on immunization: Recommendations of the Advisory Committee on Immunization Practices (ACIP). Morbidity and Mortality Weekly Report, 60(RR-2), 1–64. https://www.cdc.gov/mmwr/preview/mmwrhtml/rr6002a1.htm
- Centers for Disease Control and Prevention. (2022). Timing and spacing of immunobiologics. U.S. Department of Health & Human Services. https://www.cdc.gov/vaccines/hcp/imz-best-practices/timing-spacing-immunobiologics.html
- Centers for Disease Control and Prevention. (2024). Vaccination and immunoprophylaxis: General principles. In CDC Yellow Book: Health information for international travel. U.S. Department of Health & Human Services. https://www.cdc.gov/yellow-book/hcp/preparing-international-travelers/vaccination-and-immunoprophylaxis-general-principles.html
- World Organisation for Animal Health. (2021). Principles of veterinary vaccine production (Chapter 1.1.8). In Manual of Diagnostic Tests and Vaccines for Terrestrial Animals. https://www.woah.org/fileadmin/Home/eng/Health_standards/tahm/1.01.08_VACCINE_PRODUCTION.pdf