What is the rationale for combining vaccinations in adults?

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Last updated: May 8, 2025View editorial policy

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From the Guidelines

Combining vaccines in adults is a rational approach to improve vaccination coverage and efficiency, as supported by the most recent and highest quality study 1. Multiple vaccines can be safely administered during the same visit, which increases the likelihood of patients completing recommended immunization schedules. Common combinations include influenza and pneumococcal vaccines for older adults, Tdap (tetanus, diphtheria, pertussis) with influenza vaccines, or hepatitis A and B vaccines for travelers. The immune system is capable of responding to multiple antigens simultaneously without compromising effectiveness or safety, as demonstrated by studies such as 1 which evaluated the safety and immunogenicity of Tdap when administered simultaneously or sequentially with other vaccines. In fact, the average person encounters thousands of antigens daily, making the relatively small number in vaccines easily manageable by the immune system. Combination vaccines also reduce the number of injections needed, decreasing patient discomfort and improving adherence. This approach is particularly beneficial for adults with busy schedules who might otherwise miss follow-up appointments. While mild side effects like soreness at injection sites may occur, serious adverse reactions from receiving multiple vaccines simultaneously are rare, as noted in studies such as 1 and 1. Healthcare providers should check for contraindications before administering combined vaccines, but for most adults, this practice represents an efficient and effective approach to preventive healthcare. Some key points to consider when combining vaccines include:

  • Simultaneous administration of vaccines can increase the probability of a person being fully immunized at the appropriate age, as noted in 1.
  • The immune responses to pertussis antigens were similar when Tdap was administered simultaneously or sequentially with other vaccines, as demonstrated in 1.
  • Combination vaccines can be administered at the same visit at separate injection sites, as recommended in 1. Overall, combining vaccines in adults is a safe and effective way to improve vaccination coverage and efficiency, and healthcare providers should consider this approach when administering vaccines to their patients.

From the Research

Rationale for Combining Vaccines in Adults

  • The practice of combining vaccines in adults is supported by various studies, which highlight its safety and effectiveness 2, 3, 4.
  • Combining antigens does not increase the burden on the immune system, and it can lead to an overall reduction in adverse events 2.
  • Licensed combination vaccines undergo extensive testing before approval by regulatory authorities to ensure their safety and efficacy 2.
  • The benefits of combining vaccines include simplifying immunization schedules, reducing the number of visits to healthcare providers, and improving vaccination coverage 2, 4.

Safety and Efficacy of Combined Vaccines

  • Studies have shown that combined vaccine administration is a safe and effective practice, with benefits that outweigh the disadvantages 3, 4.
  • The immune system has the capability to respond to many millions of antigens, and adding additional vaccines through combination products does not increase the risk of adverse effects 2.
  • Combined vaccines can help improve protection against vaccine-preventable diseases and reduce the risk of complications and mortality associated with infectious diseases 4, 5, 6.

Recommendations for Vaccine Combination in Adults

  • Various vaccines are recommended for adults, including influenza, pneumococcal, zoster, and tetanus vaccines 5, 6.
  • The Advisory Committee on Immunization Practices provides detailed recommendations for the prevention of infectious diseases in target groups, including adults 5.
  • Healthcare providers can recommend and practice vaccine co-administration to improve vaccination coverage and protect against vaccine-preventable diseases 4.

References

Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

Research

Combination vaccines: defining and addressing current safety concerns.

Clinical infectious diseases : an official publication of the Infectious Diseases Society of America, 2001

Research

[Vaccine co-administration in clinical practice].

Igiene e sanita pubblica, 2018

Research

Vaccines for older adults.

The Consultant pharmacist : the journal of the American Society of Consultant Pharmacists, 2009

Research

Vaccination indications and limits in the elderly.

Acta dermatovenerologica Alpina, Pannonica, et Adriatica, 2013

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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