Effectiveness of Partial Doses of Vaccine Series
Partial vaccination provides some protection but is significantly less effective than completing the full vaccine series, with effectiveness ranging from 70% for partial vaccination to 80-84% for complete and booster vaccination. 1
General Principles of Vaccine Effectiveness
- Longer-than-recommended intervals between vaccine doses do not reduce final antibody concentrations, although full protection might not be attained until the recommended number of doses has been administered 2
- An interruption in the vaccination schedule does not require restarting the entire series of a vaccine or toxoid or adding extra doses 2
- Vaccination providers are encouraged to administer vaccines as close to the recommended intervals as possible to ensure optimal protection 2
Effectiveness by Vaccine Type
Hepatitis B Vaccine
- The standard three-dose schedule (doses at 0,1, and 6 months) is recommended for optimal protection 2
- When the vaccination series is interrupted after the first dose, the second dose should be administered as soon as possible, with at least 2 months between the second and third doses 2
- If only the third dose is delayed, it should be administered when convenient without restarting the series 2
- Partial vaccination with hepatitis B vaccine provides some protection, but the third dose confers optimal protection by acting as a booster dose 2
COVID-19 Vaccines
- Partial vaccination with inactivated COVID-19 vaccines shows an effectiveness of 70.18% (95% CI 57.33-83.02) 1
- Complete vaccination increases effectiveness to 79.52% (95% CI 67.88-91.71) 1
- Booster vaccination provides the highest protection at 84.22% (95% CI 74.34-94.10) 1
- For COVID-19, vaccination alone (even with complete series) may be insufficient to fully contain outbreaks without additional non-pharmaceutical interventions 3
Haemophilus influenzae type b (Hib) Vaccines
- If different brands of Hib conjugate vaccine are administered, a total of three doses is considered adequate for the primary series among infants 2
- Any of the licensed conjugate vaccines can be used for the recommended booster dose at 12-18 months of age 2
Interchangeability of Vaccines
- Available data indicate that infants who receive sequential doses of different Hib conjugate, hepatitis B, and hepatitis A vaccines produce a satisfactory antibody response after a complete primary series 2
- All brands of Hib conjugate, hepatitis B, and hepatitis A vaccines are interchangeable within their respective series 2
- When at least one dose of a hepatitis B vaccine produced by one manufacturer is followed by subsequent doses from a different manufacturer, the immune response has been comparable with that resulting from a full course of vaccination with a single vaccine 2
Clinical Implications and Recommendations
- Complete vaccination should be the primary goal for all patients to achieve optimal protection against disease 1
- For patients with interrupted vaccination schedules:
- For patients with unknown or uncertain vaccination status:
- Only accept written, dated records as evidence of vaccination 2
- Consider persons without documentation as susceptible and start them on the age-appropriate vaccination schedule 2
- Serologic testing for immunity is an alternative for certain antigens (e.g., measles, mumps, rubella, varicella, tetanus, diphtheria, hepatitis A, hepatitis B, and poliovirus) 2
Common Pitfalls and Caveats
- Delaying vaccination because the brand used for previous doses is not available or is unknown is not recommended 2
- Self-reported doses of vaccine without written documentation should not be accepted (except for pneumococcal polysaccharide vaccine) 2
- Protection against infection may wane more quickly than protection against severe outcomes, as seen with COVID-19 vaccines 4
- Vaccine effectiveness may vary by: