Proteins are like carefully folded pieces of origami. Their three-dimensional structure largely determines their purpose and in vivo activity. But proteins are delicate molecules that can lose their shape or denature. Heat, moisture and chemical reactions can all cause denaturation. Once the protein shape changes, it is often no longer able to carry out its purpose.
In the case of proteins delivered in vaccines, the immune system may no longer recognize the protein or make an effective immune response against the pathogen, affecting vaccine effectiveness. For this reason, some vaccines are manufactured and stored as two components: a freeze-dried component and a liquid component. How these components are handled directly affects the ability of the vaccine to train the immune system. Let’s take a closer look.
The freeze-dried component
Many chemical reactions that lead to degradation require water. As such, by removing water through lyophilization (freeze-drying), processes that cause protein breakdown slow significantly. Vaccines that have a freeze-dried component remain stable for months, or even years, facilitating transport and storage.
To freeze-dry a vaccine, the near-final product is frozen, and the water is removed under vacuum conditions. It is supplied as a powder or pellet in a sterile glass vial with specific labeling indicating the vial contents.
The liquid component
The liquid component is known as the diluent. It is a specific, sterile liquid used to reconstitute the freeze-dried component of the vaccine. Diluents can be sterile water, sodium chloride, buffer, or even the adjuvant suspension, among others. Typically, this should be done right before administration of the vaccine. This timing helps ensure that the vaccine is administered at the correct concentration and that proteins retain their proper three-dimensional form. Notably, once liquid is reintroduced, the chemical reactions slowed by freeze-drying resume, leading to the same concerns about stability and shelf life that led to freeze-drying in the first place. For this reason, manufacturers establish specific time limits for vaccine use after reconstitution.
Mixing the vaccine components: More than meets the eye
Diluents do much more than convert a powder into a liquid that can be administered. While some diluents may appear to be simple solutions, they are carefully formulated to ensure that the vaccine being administered has the proper pH, salt concentration, and stability after mixing. Diluents are also designed to be compatible with other vaccine components, including adjuvants when present. In some combination products, one vaccine component is supplied in the diluent while another is supplied as a freeze-dried powder, making both components necessary to deliver the complete vaccine dose. Prior to administration, the liquid is typically added to the glass vial of the freeze-dried component.
For example, the MMR vaccine is provided in two vials. One contains the freeze-dried component, and the other contains sterile water. At times, the sterile water may be packaged in a syringe instead of a vial. A package with 10 doses will therefore contain 10 vials of each component, or 10 vials plus 10 syringes. The package insert provides instructions on how to mix the components, including the allowable time between reconstitution and administration and how long the dose may be stored in its reconstituted form prior to discarding.
Because of the need to prepare the vaccine prior to administration, diluent-related errors are among the more common vaccine administration errors. Examples of common errors include:
- Mixing one vaccine with another vaccine's diluent
- Using sterile water or normal saline instead of the supplied diluent
- Administering the diluent alone without adding the freeze-dried component
- Using the wrong volume of diluent
Storage and handling issues can also contribute to diluent-related errors, including:
- Storing the vaccine or diluent at an incorrect temperature
- Separating diluents from their corresponding vaccines
- Confusing products with similar packaging
- Administering a reconstituted vaccine beyond the time permitted in the package insert
Mixing the vaccine components: How to avoid errors
Providers can reduce the risk of diluent-related errors by following several best practices:
- Store diluents with their corresponding vaccines whenever possible.
- Verify both the vaccine and diluent during preparation.
- Follow manufacturer-specific reconstitution instructions, including the amount of diluent to use, as described in package inserts.
- Post easy-to-use resources in vaccine reconstitution areas for reference, such as Immunize.org’s “Vaccine Diluents: How to Use Them.”
- Administer vaccines immediately or within the permitted time window after reconstitution.
- Include diluent verification in vaccine preparation workflows, competency assessments, and staff training programs.
When a diluent error occurs, the appropriate response depends on the specific vaccine and error. In some cases, the dose may need to be repeated immediately. In others, the dose may be considered valid. As recommendations regarding revaccination may differ by vaccine and error type, providers should consult the vaccine package insert, the manufacturer or resources from specialized groups like Immunize.org when determining how to proceed. For example, on the Immunize.org website, many questions have been answered in the “Ask the Experts” section, which can be searched by the vaccine name or using keywords related to the specific administration issue.
As with many vaccine administration errors, it’s also critical to identify why the error occurred and implement strategies to prevent recurrence. In addition:
- Be sure that staff feel the work environment is supportive for reporting any errors that are made.
- Ensure that one of the steps includes the process for informing the family of the error.
- Regardless of type, all errors should be reported to the Vaccine Adverse Event Reporting System (VAERS).
Staff education, storage improvements, labeling systems and vaccine preparation workflows can all help reduce future errors.
The bottom line
Diluents help ensure that vaccines work as intended at the time of administration. In many cases, vaccine effectiveness depends as much on chemistry and formulation science as it does on immunology.
Resources
- Red Book: Vaccine Administration (login required)
- Vaccine Diluents: How to Use Them
Proteins are like carefully folded pieces of origami. Their three-dimensional structure largely determines their purpose and in vivo activity. But proteins are delicate molecules that can lose their shape or denature. Heat, moisture and chemical reactions can all cause denaturation. Once the protein shape changes, it is often no longer able to carry out its purpose.
In the case of proteins delivered in vaccines, the immune system may no longer recognize the protein or make an effective immune response against the pathogen, affecting vaccine effectiveness. For this reason, some vaccines are manufactured and stored as two components: a freeze-dried component and a liquid component. How these components are handled directly affects the ability of the vaccine to train the immune system. Let’s take a closer look.
The freeze-dried component
Many chemical reactions that lead to degradation require water. As such, by removing water through lyophilization (freeze-drying), processes that cause protein breakdown slow significantly. Vaccines that have a freeze-dried component remain stable for months, or even years, facilitating transport and storage.
To freeze-dry a vaccine, the near-final product is frozen, and the water is removed under vacuum conditions. It is supplied as a powder or pellet in a sterile glass vial with specific labeling indicating the vial contents.
The liquid component
The liquid component is known as the diluent. It is a specific, sterile liquid used to reconstitute the freeze-dried component of the vaccine. Diluents can be sterile water, sodium chloride, buffer, or even the adjuvant suspension, among others. Typically, this should be done right before administration of the vaccine. This timing helps ensure that the vaccine is administered at the correct concentration and that proteins retain their proper three-dimensional form. Notably, once liquid is reintroduced, the chemical reactions slowed by freeze-drying resume, leading to the same concerns about stability and shelf life that led to freeze-drying in the first place. For this reason, manufacturers establish specific time limits for vaccine use after reconstitution.
Mixing the vaccine components: More than meets the eye
Diluents do much more than convert a powder into a liquid that can be administered. While some diluents may appear to be simple solutions, they are carefully formulated to ensure that the vaccine being administered has the proper pH, salt concentration, and stability after mixing. Diluents are also designed to be compatible with other vaccine components, including adjuvants when present. In some combination products, one vaccine component is supplied in the diluent while another is supplied as a freeze-dried powder, making both components necessary to deliver the complete vaccine dose. Prior to administration, the liquid is typically added to the glass vial of the freeze-dried component.
For example, the MMR vaccine is provided in two vials. One contains the freeze-dried component, and the other contains sterile water. At times, the sterile water may be packaged in a syringe instead of a vial. A package with 10 doses will therefore contain 10 vials of each component, or 10 vials plus 10 syringes. The package insert provides instructions on how to mix the components, including the allowable time between reconstitution and administration and how long the dose may be stored in its reconstituted form prior to discarding.
Because of the need to prepare the vaccine prior to administration, diluent-related errors are among the more common vaccine administration errors. Examples of common errors include:
- Mixing one vaccine with another vaccine's diluent
- Using sterile water or normal saline instead of the supplied diluent
- Administering the diluent alone without adding the freeze-dried component
- Using the wrong volume of diluent
Storage and handling issues can also contribute to diluent-related errors, including:
- Storing the vaccine or diluent at an incorrect temperature
- Separating diluents from their corresponding vaccines
- Confusing products with similar packaging
- Administering a reconstituted vaccine beyond the time permitted in the package insert
Mixing the vaccine components: How to avoid errors
Providers can reduce the risk of diluent-related errors by following several best practices:
- Store diluents with their corresponding vaccines whenever possible.
- Verify both the vaccine and diluent during preparation.
- Follow manufacturer-specific reconstitution instructions, including the amount of diluent to use, as described in package inserts.
- Post easy-to-use resources in vaccine reconstitution areas for reference, such as Immunize.org’s “Vaccine Diluents: How to Use Them.”
- Administer vaccines immediately or within the permitted time window after reconstitution.
- Include diluent verification in vaccine preparation workflows, competency assessments, and staff training programs.
When a diluent error occurs, the appropriate response depends on the specific vaccine and error. In some cases, the dose may need to be repeated immediately. In others, the dose may be considered valid. As recommendations regarding revaccination may differ by vaccine and error type, providers should consult the vaccine package insert, the manufacturer or resources from specialized groups like Immunize.org when determining how to proceed. For example, on the Immunize.org website, many questions have been answered in the “Ask the Experts” section, which can be searched by the vaccine name or using keywords related to the specific administration issue.
As with many vaccine administration errors, it’s also critical to identify why the error occurred and implement strategies to prevent recurrence. In addition:
- Be sure that staff feel the work environment is supportive for reporting any errors that are made.
- Ensure that one of the steps includes the process for informing the family of the error.
- Regardless of type, all errors should be reported to the Vaccine Adverse Event Reporting System (VAERS).
Staff education, storage improvements, labeling systems and vaccine preparation workflows can all help reduce future errors.
The bottom line
Diluents help ensure that vaccines work as intended at the time of administration. In many cases, vaccine effectiveness depends as much on chemistry and formulation science as it does on immunology.
Resources
- Red Book: Vaccine Administration (login required)
- Vaccine Diluents: How to Use Them