Introduction

Vaccines are delicate biological substances. They lose their ability to protect against disease when exposed to temperatures that are too high or too low. The system that keeps vaccines at the right temperature - from the manufacturer to the child - is called the cold chain .

A vaccine carrier is a small, insulated container that is a key part of this cold chain. It holds vaccines safely during transportation from a health facility to vaccination sites - including remote villages, schools, and community centers where refrigeration is not available.

Without a properly used vaccine carrier, vaccines can silently lose their potency. A child may receive an injection, but the vaccine may no longer work. This makes correct use of vaccine carriers essential to any immunization program.

Purpose and Where It Is Used

Primary Purpose

The main purpose of a vaccine carrier is to maintain vaccines at a safe temperature (between +2°C and +8°C) during transport from a refrigerated facility to the point of vaccination, and to keep them at this temperature throughout the immunization session.

Where Vaccine Carriers Are Used

• Outreach immunization sessions - vaccinating children in communities far from a health facility
• Mobile immunization campaigns - national immunization days, supplementary immunization activities (SIAs)
• School-based vaccination programs - where no refrigerator is available on site
• Last-mile delivery - transporting vaccines on foot, bicycle, motorcycle, or other transport in difficult terrain
• Temporary storage - during a health post session while a refrigerator is being defrosted or repaired
• Disaster response - emergency vaccination in flood-affected, conflict-affected, or displaced populations

Cold Chain Position

The vaccine carrier represents the final stage of the cold chain - from health facility to patient. The complete cold chain typically flows as: manufacturer - national cold store - regional cold store - district store - health facility refrigerator - vaccine carrier - vaccination site.

Types of Vaccine Carriers

Vaccine carriers are classified by WHO under the Performance, Quality and Safety (PQS) system as category E004 . Two main types exist:

1. Standard Vaccine Carrier (SVC)

The traditional type, used widely in immunization programs worldwide. It requires conditioned ice packs (see User Guide section). Freeze-sensitive vaccines must never come into direct contact with frozen ice packs in this carrier.

2. Freeze-Preventive Vaccine Carrier (FPVC)

A newer design with a built-in insulated barrier that physically separates the vaccine compartment from the frozen ice packs. This prevents vaccines from freezing even when frozen ice packs are used. The WHO and UNICEF have published guidance supporting the use of FPVCs, particularly in programs where freeze-sensitive vaccines are used.

By Construction Material

• Hard-shell carriers - rigid plastic exterior, more durable, suitable for rough transport conditions (vehicles over rough roads)
• Soft-shell carriers - flexible canvas or fabric exterior, lighter, better for walking and hand-carrying; some come with backpack straps for ergonomic carrying

By Capacity

WHO PQS specifications state that vaccine carriers have a vaccine storage capacity of between 0.1 and 5.0 litres. They are designed for a maximum fully loaded weight of 8 kg or less. The right size depends on the number of children to be vaccinated, distance to be traveled, and duration of the session.

Vaccine Carrier vs Cold Box

A cold box is larger than a vaccine carrier (storage capacity over 5 litres, maximum load up to 50 kg) and is used at higher levels of the supply chain for bulk transport or extended temporary storage (up to several days). A vaccine carrier is smaller and used for last-mile, same-day outreach and sessions.

How to Use a Vaccine Carrier - Step by Step

Before the Session

1. 1

   Prepare ice packs in advance. Place the required number of water packs (ice packs) in the freezer. Each vaccine carrier model requires a specific number and size of ice packs - always follow the instructions printed on or inside the lid. It is recommended to have two sets of ice packs so that one set is always frozen and ready.

2. 2

   Condition the ice packs (Standard Carrier only). Frozen ice packs must NOT be placed directly against vaccines in a standard carrier. Conditioning means allowing the ice packs to thaw slightly until water starts to drip from their surface (usually 5-10 minutes at room temperature). A conditioned ice pack is half solid and half liquid. This step prevents freeze-sensitive vaccines from being damaged.

3. 3

   Note for Freeze-Preventive Carriers: No conditioning is needed. Frozen ice packs can be placed directly into the FPVC. Do NOT use conditioned or cool water packs in an FPVC - they are designed specifically for frozen packs.

4. 4

   Line the carrier with ice packs. Place conditioned ice packs (or frozen packs in an FPVC) at the bottom and sides of the vaccine carrier as per the carrier's instructions.

5. 5

   Check vaccine vial monitors (VVMs) before loading. Before placing any vaccine into the carrier, inspect the VVM on each vial. Use only vaccines with a usable VVM reading (see VVM section below).

6. 6

   Load the vaccines. Place vaccines in their secondary packaging (carton boxes or polythene bags) in the center of the carrier. In a standard carrier, never allow vaccine vials to touch the ice packs directly. Vaccines that are most heat-sensitive (such as OPV) or that have the most advanced VVM should be placed on top and used first.

7. 7

   Place the foam pad insert (if provided). Many carriers come with a foam pad insert. Place it on top of the vaccines before closing the lid. It acts as an insulating layer and a surface to rest vials during the session without removing them from the carrier.

8. 8

   Close and seal the lid. Close the lid firmly and check that it is properly sealed. Write the time of sealing if needed. The cold life clock starts from this moment.

During the Session

1. 1

   Keep the lid closed as much as possible. Each time the lid is opened, warm air enters and the cold life shortens. Open the lid only to take out vaccines and close it immediately.

2. 2

   Use the foam pad surface for vials in use. Rest the vials being used on the foam pad surface, not on the ground or table. Return unused vials to the carrier and close the lid.

3. 3

   Keep the carrier in shade. Never place the vaccine carrier in direct sunlight. Sunlight heats the exterior and reduces cold life significantly. Some vaccines (BCG, measles, MMR, rubella) are also sensitive to light and can lose potency when exposed to it.

4. 4

   Monitor ice pack status. When ice packs become fully liquid (all water, no solid), they should be replaced. Fully defrosted ice packs at +5°C can reach +20°C within 10 hours at ambient temperatures of +43°C - this is not safe.

5. 5

   Do not place reconstituted vaccines directly on ice packs. This practice (placing a vial in the hole in an ice pack) is no longer recommended by WHO. It may cause the vaccine to freeze, damaging it.

After the Session

1. 1

   Return unused vaccines to the refrigerator promptly. After the session, check VVM status on returned vials. Place vaccines with advanced VVM status in a "use first" section of the refrigerator and use them at the next session before opening new vials.

2. 2

   Discard reconstituted vaccines that were opened but not fully used. Reconstituted (mixed) vaccines such as BCG and measles that were opened must be discarded at the end of the session or within 6 hours of opening - whichever comes first - unless the national multi-dose vial policy allows otherwise.

3. 3

   Clean and dry the carrier. Remove ice packs, wipe out any water, and allow the carrier to dry. Store it open and clean, ready for the next use.

4. 4

   Return ice packs to the freezer for the next use. Check packs for any cracks or leaks and discard damaged ones.

Reading the Vaccine Vial Monitor (VVM)

A Vaccine Vial Monitor (VVM) is a small heat-sensitive label attached to each vaccine vial by the manufacturer. It changes colour as the vaccine is exposed to heat over time. It is the single most important tool for checking whether a vaccine is still safe to use.

The VVM consists of a dark outer circle and a lighter inner square . As heat exposure accumulates, the inner square darkens. The VVM does not detect freezing damage - only heat damage.

There are four VVM types: VVM2, VVM7, VVM14, and VVM30. The number refers to the number of days it takes for the VVM to reach its discard point at a constant temperature of 37°C. Each vaccine type uses the VVM category that matches its heat sensitivity.

Precautions and Dangers

Temperature Dangers

The Shake Test (for Freeze-Sensitive Vaccines)

If freezing is suspected (e.g., ice packs were not conditioned, or the session was in a very cold environment), a shake test helps identify damaged vaccines.

• Shake the suspect vial and an identical vial known to be good (control)
• Hold both up to the light after shaking
• If the suspect vial clears slowly or forms more sediment than the control, it has likely been frozen and damaged
• Discard any vaccine that fails the shake test

Light Sensitivity

BCG, measles, measles-rubella (MR), MMR, and rubella vaccines are sensitive to both heat and light. These should be kept in their secondary packaging (dark glass vials or cartons) inside the carrier and never exposed to direct sunlight or strong artificial light.

Other Precautions

• Always check that ice packs are properly fitted - improperly placed packs leave gaps that warm rapidly
• Never use a cracked or leaking ice pack - a leaking pack will wet vaccine labels, making vials unidentifiable
• Never add non-vaccine items (food, drinks, medications not part of the immunization session) to the carrier
• Never leave the carrier unattended in a hot vehicle or in direct sun
• Never use a carrier whose insulation has been compressed, cracked, or damaged - it will not maintain temperature correctly
• Always use WHO PQS-prequalified ice packs with the specific carrier model they were designed for - mismatched packs will reduce cold life
• Expired vaccines must never be placed in the carrier, even if the VVM appears normal

What to Do If Ice Packs Completely Melt During a Session

• Discard all vials of reconstituted vaccines (e.g., BCG, measles) immediately
• Check VVM status on all remaining unopened vials
• Return any unopened vials with usable VVMs to the refrigerator as quickly as possible
• Place these vials in the "use first" section for the next session
• Do not use any vaccine whose VVM has reached or passed the discard point

Key Technical Specifications (WHO PQS)

Frequently Asked Questions

How to Keep the Vaccine Carrier in Good Condition

Cleaning

• After each use, remove all ice packs, dry any water inside, and wipe the interior with a clean cloth
• If there is visible soiling, clean with a mild disinfectant solution and wipe dry
• Never submerge the carrier in water - this can damage the insulating foam inside
• Leave the lid open after cleaning to allow complete drying before the next use

Inspection

• Regularly inspect the lid seal (gasket) for cracks, hardening, or damage - a damaged seal reduces temperature performance significantly
• Check the outer shell for cracks or impact damage, especially in hard-shell carriers
• Press gently on the lid when closed - there should be no air gaps around the seal
• If the insulation feels crushed or compressed, the carrier may no longer meet its rated cold life
• Inspect ice packs before each use for cracks, leaks, or contamination

Storage

• Store the carrier in a clean, cool, dry place - away from direct sunlight and rodents
• Store with the lid slightly open to prevent mould growth inside
• Do not stack heavy items on top of carriers as this can compress and damage the insulation
• Keep ice packs stored flat in the freezer, not stacked under other heavy objects

Replacement Indicators

Additional Important Points

Environmental Considerations

WHO and UNICEF advise that vaccine carriers and cold boxes manufactured using environmentally safer foaming agents (such as cyclopentane) are preferred over those using older chemicals like R141b, which contribute to ozone depletion. Products using CFCs are no longer accepted under WHO PQS standards.

Cool Water Packs and Warm Water Packs

In some settings, ice packs may not be available in a frozen state. Cool water packs (water packs cooled to +2°C to +8°C, not frozen) completely eliminate the risk of vaccine freezing in standard carriers and can be used for short-duration sessions. However, they have a shorter cold life than frozen packs. Warm water packs can be used in very cold climates to protect vaccines from freezing during transport - they act as an insulating barrier between vaccines and the cold environment.

Phase Change Material (PCM)

Some newer vaccine carriers and cold boxes use Phase Change Material (PCM) instead of traditional ice packs. PCM packs use substances that change state (from solid to liquid or vice versa) at specific temperatures, providing more precise temperature control. These are particularly useful for maintaining temperatures within the +2°C to +8°C range without requiring a freezer. PCM-based carriers are an emerging technology supported by WHO and are being progressively introduced in some national programs.

Multi-Dose Vial Policy (MDVP)

The WHO Multi-Dose Vial Policy governs whether opened vaccine vials can be returned to the refrigerator and used in future sessions. Under updated MDVP guidance, opened vials of certain WHO prequalified vaccines with preservative can be reused for up to 28 days if they meet specific conditions (VVM usable, cold chain maintained, not contaminated, not expired). This is different for lyophilized (freeze-dried) vaccines like BCG and measles, which must be discarded within 6 hours of reconstitution. National programs publish specific MDVP guidance that should always be followed.

Ice Pack Standardization

Where possible, a program should use only one size and model of ice pack across all carriers. This simplifies logistics, prevents errors, and ensures the right number of packs are always available for each carrier type.