Immunization Module: The Cold Chain

Study Session 6  The Cold Chain

Introduction

In this study session you will learn about the cold chain — the equipment and procedures that you will use to keep vaccines within the correct temperature range (between 2^oC and 8^oC), so that they remain in good condition. Vaccines should be stored carefully at all times, beginning at the factory where they are manufactured and at every stage until the moment they are given to children and mothers. Excess heat or cold will reduce the vaccine potency (strength), increasing the risk that recipients will not be protected against vaccine-preventable diseases.

The cold chain has three main components: equipment for vaccine transport and storage, well-trained personnel, and efficient management procedures. In this study session, and the next two sessions, you will learn how all three components are required to ensure that vaccines are transported and stored safely.

Learning Outcomes for Study Session 6

• 6.1  Define and use correctly all of the key words printed in bold. (SAQs 6.1 and 6.2)
• 6.2  Describe the common types of cold chain equipment and their uses in your Health Post. (SAQs 6.1, 6.2, 6.5 and 6.6)
• 6.3  Describe how you can monitor the effectiveness of the cold chain for vaccines at your Health Post and when you are transporting vaccines. (SAQs 6.1, 6.2, 6.5 and 6.7)
• 6.4  Describe how vaccines can be spoiled and how to prevent this from happening. (SAQs 6.4, 6.6 and 6.7)
• 6.5  Describe how to load vaccines and diluents correctly into cold chain equipment. (SAQ 6.3, 6.4 and 6.6)
• 6.6  Briefly describe how to maintain cold chain equipment (undertake minor repairs). (SAQs 6.5 and 6.7)

6.1  Components of the cold chain

The cold chain has three main components, each of which must combine to ensure safe vaccine transport and storage:

• transport and storage equipment
• trained personnel
• efficient management procedures.

This study session is about the first of these components. You can see the cold chain equipment in Figure 6.1, together with the storage temperatures required at each storage place, from arrival in the country to the storage in your Health Post. Next we will describe the common cold chain equipment you will use when you collect vaccines from the health centre and in your practice at the Health Post and in the community.

Figure 6.1  The cold chain. (Adapted from: WHO, 2004, Immunization in Practice, Module 3, The Cold Chain, Figure 3A, p.2)

6.2  Cold chain equipment in Health Posts

The common cold chain equipment used in Health Posts are refrigerators, cold boxes, vaccine carriers, ice-packs and foam pads. In this section, the correct use of each of these will be described.

6.2.1  Refrigerators

A refrigerator is a cooling apparatus. Health facility refrigerators may be powered by electricity, kerosene, paraffin, bottled gas or solar energy. Electric refrigerators are usually the least costly to run and the easiest to maintain, but they must have a reliable electricity supply, which is not often possible in rural Health Posts in Ethiopia. Different refrigerators have different capacities for storing vaccines and for freezing and storing ice-packs (Figure 6.2).

Figure 6.2  A Health Extension Worker with a kerosene-powered refrigerator in a rural Health Post in SNNPR, Ethiopia. This refrigerator has a freezer compartment on top, and plenty of space for the vaccines, diluents and other supplies that must be kept cold. (Photos: Janet Haresnape)

A refrigerator in a Health Post should be able to hold:

• One month’s supply of vaccines and diluents in the refrigerator compartment.
• A minimum stock of one to two weeks’ supply of vaccines and diluents (i.e. an additional 25% of the standard stock).
• Frozen ice-packs (strong, specially made plastic bottles containing frozen water) standing in the freezer compartment for at least 24 hours to become fully frozen.
• 

  Do not put frozen ice-packs into the main refrigerator compartment! They could cause the temperature to drop too low and destroy the freeze-sensitive vaccines.
  Unfrozen chilled ice-packs in the refrigerator compartment (Figure 6.3); they help to keep the refrigerator cold for a while if there is a power failure. You can also keep ordinary plastic bottles filled with chilled water in the refrigerator for the same purpose.

Figure 6.3  These unfrozen (chilled water) ice-packs help to keep the refrigerator cold during a power failure. They should always be stored vertically to avoid possible leaks. (Photo: Basiro Davey)

6.2.2  Cold boxes and vaccine carriers

A cold box is an insulated container that can be lined with ‘conditioned’ ice-packs to keep vaccines and diluents cold — but not frozen — during transportation of vaccine supplies from the health centre, or to outreach sites. (We will explain what ‘conditioning’ ice-packs means in the next section.) Cold boxes can also be used for short periods of vaccine storage (from two to seven days, depending on the manufacturer) when the refrigerator is out of order or being defrosted, or if vaccines are being transported in a vehicle for a few days by mobile immunization teams.

Cold boxes are quite large. At Health Post level you may instead use a smaller insulated container called a vaccine carrier (Figure 6.4). Vaccine carriers are also lined with conditioned ice-packs to keep vaccines and diluents cold during transportation from the collection store at the health centre, or on journeys to outreach sites, and for temporary storage during Health Post immunization sessions. They are smaller than cold boxes and are easier to carry if walking, but they do not stay cold for as long — at most 36–48 hours with the lid closed (depending on the type).

Figure 6.4 (a) A vaccine carrier lined with conditioned ice-packs. (b) This type of vaccine carrier stays cold for a maximum of 36 hours if the lid remains closed. (Photo: Basiro Davey)

6.2.3  Ice-packs

Ice-packs are flat, rectangular plastic bottles filled with water and then either kept at refrigerator temperature (Figure 6.3 above), or frozen and then conditioned for use in vaccine carriers and cold boxes (Figure 6.4a). The number of ice-packs required for a cold box or vaccine carrier varies.

Every Health Post should have a minimum of two sets of ice-packs for each of their cold boxes and vaccine carriers, one in the process of being frozen or refrigerated, and the other conditioned for use in a cold box or vaccine carrier.

6.2.4  Foam pads

A foam pad is a piece of soft foam that fits on top of the conditioned ice-packs in a cold box or a vaccine carrier (Figure 6.5). There are some cuts in the foam to allow vaccine vials to be inserted in the pad. During immunization sessions, the foam pad can be used as a temporary lid to keep unopened vaccines inside the carrier cool, while providing a surface to hold and protect opened vaccine vials and keep them cool (Figure 6.6). Vaccines are protected from heat damage during an immunization session if they are inserted in the foam pad above the ice-packs in the vaccine carrier.

Figure 6.5  The foam pad in a vaccine carrier has cuts to hold vials and vaccines during an immunization session. (Photo: Janet Haresnape)

Figure 6.6  Foam pad with vaccine vials inserted. (Source: WHO, 2004, as in Figure 6.1, p.8)

6.3  Cold chain monitoring equipment in your Health Post

It is important to know about the common cold chain monitoring equipment for keeping a record of the temperature that vaccines and diluents are exposed to during transportation and storage. The items of equipment used are vaccine vial monitors, freeze indicators and thermometers.

6.3.1  Vaccine vial monitors

A vaccine vial monitor (VVM) is a label that changes colour when the vaccine vial or ampoule has been exposed to temperatures above 8ºC over a period of time. Before opening a vaccine container, the status of the VVM must be checked to see whether the vaccine has been damaged by heat. Manufacturers attach VVMs to vials and ampoules of most vaccines. The VVM is printed on the label or cap, or the neck of ampoules of freeze-dried vaccines (Figure 6.7). It looks like a square inside a circle. As the vaccine vial is exposed to more heat, the square becomes darker.

Figure 6.7  (a) Vaccine Vial Monitors (VVMs) on the neck of an ampoule, or on the label or cap of a vaccine vial (Source: WHO, 2004, as in Figure 6.1, p.10). (b) A vial of liquid PCV10 vaccine (Synflorix) with the VVM on the cap (Photo: WHO).

Do not use vaccines that have reached the discard point, even if they have not passed their expiry date!

You should only use vaccines where the inner square in the VVM is lighter in colour than the outside circle (Figure 6.8, top row). Vials with VVMs in which the inner square has begun to darken, but is still lighter than the outer circle (Figure 6.8, second row), should be used first, i.e. before vials where the VVM square has not begun to darken. Vials with VVMs in which the inner square matches the colour of the outer square, or in which the inner square is darker than the outer circle, have reached or gone beyond the discard point and should not be used (Figure 6.8, bottom two rows).

Figure 6.8  How to read a vaccine vial monitor (VVM). (Source: WHO, 2004, as in Figure 6.1, p.11)

6.3.2  Freeze indicators

Freeze indicators are devices used to monitor the exposure of vaccines to freezing. Freeze indicators are packed with batches of freeze-sensitive EPI vaccines (pentavalent, PCV10 and TT), as well as with other freeze-sensitive vaccines such as HepB, which may be used to protect healthcare workers. The most commonly used type of freeze indicator is the freeze-tag (Figure 6.9). This is an irreversible temperature indicator that shows if a product, such as a vaccine, has been exposed to freezing. It consists of an electronic temperature measuring circuit with a liquid crystal display (LCD). A small blinking dot of light in the corner of the display shows that the freeze-tag is functioning correctly.

Figure 6.9  Freeze-tags showing: (a) ‘good status’ display; (b) ‘alarm status’ display. (Photo: WHO)

If the freeze-tag is exposed to a temperature below 0^oC (with a range between +0.3 ^oC and –0.3 ^oC) for more than 60 minutes (with a range of between 57 to 63 minutes), the display will change from the ‘good status’ (Figure 6.9a) to the ‘alarm status’ (Figure 6.9b).

Vaccines that have been exposed to freezing may have been damaged and should be checked by using the shake test, as described below.

6.3.3  The shake test

The shake test is how you check whether freeze-sensitive vaccines (pentavalent, PCV10, TT or HepB) have been subjected to freezing temperatures, which are likely to have damaged them. To perform the shake test, follow the steps below:

Step 1 — Prepare a frozen control vial: Take a vial of vaccine of the same type and batch number as the vaccine you want to test, and from the same manufacturer. Freeze the vial until the contents are solid (at least 10 hours at –10°C) and then let it thaw. This is the frozen control vial (the middle vial in Figure 6.10). Mark the vial clearly so that it is easily identifiable and will not be used by mistake.

Step 2 — Choose a test vial: Take a vial (or vials) of vaccine from the batch that you suspect has been frozen. This is the suspected frozen test vial (on the left in Figure 6.10).

Step 3 — Shake the control and test vials: Hold the frozen control vial and the suspected frozen test vial together in one hand and shake them vigorously for 10–15 seconds.

Step 4 — Allow the vials to rest: Leave both vials to rest by placing them on a table side by side and not moving them further. A freeze-sensitive vaccine that has not been frozen appears as a uniformly cloudy liquid (see the vial on the right in Figure 6.10). After freezing, the vaccine tends to form flakes that quickly settle at the bottom of the vial to form a sediment when you leave it to rest after vigorous shaking. The speed at which the flakes settle is called the sedimentation rate. Note that some vials have large labels that conceal the vial contents. This makes it difficult to see the sedimentation process. In such cases, turn the control and test vials upside down and observe sedimentation taking place in the neck of the vials.

Step 5 — Compare the vials: Observe the difference in sedimentation rates in the frozen control and suspected frozen test vials for a maximum of 30 minutes. View both vials against the light to compare the sedimentation rate. If the vaccine in the suspected test vial shows a much slower sedimentation rate than the vaccine in the frozen control vial, you can conclude that the test vaccine has most probably not been frozen and can be used.

Figure 6.10  Three vials of liquid freeze-sensitive vaccine viewed with the light behind them: (left) frozen test vial in which a sediment has settled to the bottom of the vial after vigorous shaking; (centre) frozen control vial in which the sedimentation rate can be compared with the rate in a suspected frozen test vial; (right) non-frozen test vial showing the uniformly cloudy appearance of a vaccine that has not been damaged by freezing. (Photo: WHO)

The shake test should be conducted for all vaccines with the following characteristics:

• Vaccines packed in boxes that have a freeze indicator (e.g. freeze tag, see Figure 6.9), which is found to be activated.
• Refrigerator temperature records that show the temperature has fallen below +2ºC.
• Where you suspect that the vaccines may have been frozen by mistake, for example by placing too close to the freezer plate in the refrigerator, or touching frozen ice-packs.

If the vaccine fails the ‘shake test’ it must be discarded. There is no need to conduct a shake test if a liquid vaccine vial is already frozen solid — simply discard it. Also discard any vials that develop white lumps of sediment attached to the glass, which cannot be dispersed despite vigorous shaking. This can happen if pentavalent vaccine is exposed to freezing below 0ºC.

6.3.4  Thermometers

Figure 6.11  (a) Dial thermometer, and (b) stem thermometer. (Source: WHO, 2004, as in Figure 6.1, p.13)

A thermometer is an instrument for monitoring the temperature of your cold chain equipment — refrigerator, cold box or vaccine carrier. It enables you to adjust the temperature to the correct range for the storage and transport of vaccines.

At a Health Post, either a dial or a stem (bulb) thermometer may be used to monitor the equipment temperature. On a dial thermometer, the needle moves around the scale, pointing to plus (+) numbers when it is warmer, and to minus (–) numbers when it is colder (Figure 6.11a). On a stem (or bulb) thermometer, coloured fluid in the bulb moves up the scale as it becomes warmer, and down the scale as it becomes colder (Figure 6.11b).

6.4  How to load cold chain equipment

Refrigerators, cold boxes and vaccine carriers must be loaded correctly to keep the temperature of the vaccines and diluents inside within the acceptable range. All health workers in a Health Post should know how to monitor the cold chain equipment and what action to take if the temperature is too high or too low.

6.4.1  The design of vaccine refrigerators

All electric powered refrigerators have a thermostat. The thermostat is a device that automatically responds to temperature changes by activating switches controlling the cooling equipment to maintain the refrigerator compartments at the correct temperature. You can alter the setting of the thermostat if the temperature of the refrigerator is found to be too high or too low when you check the thermometer. Gas or kerosene refrigerators are adjusted by altering the size of the flame.

To ensure that the refrigerator is effective for storing your vaccines, there are a number of guidelines that you should follow (Box 6.2).

There are a number of different types of refrigerator. Some front-loading refrigerators have one door, with a second freezing compartment inside. Others have two separate compartments, with different doors (look back at Figure 6.2, and see the diagram in Figure 6.12).

Maximise

Figure 6.12  Front-loading refrigerator with separate freezing compartment on top. (Source: WHO, 2004, as Figure 6.1, p.18)

The two compartments shown in Figure 6.12 should be used as follows:

• The main compartment (the refrigerator), in which the temperature should be kept between +2ºC and +8ºC, is used for storing vaccines and diluents.
• The top compartment (the freezer) is used for freezing ice-packs. If the refrigerator is working properly, this compartment will be between –15ºC and –20ºC.

Notice the ‘use first’ box, for multi-dose vaccines that have been opened, or unopened vials that have been taken out for an immunization session but not used. These vials should be used before other vials.

Remember that you must not return opened vials of PCV10 vaccine to the refrigerator; it is a liquid vaccine without preservative and once it is opened any remaining vaccine in the two-dose vial should be discarded after six hours or at the end of the immunization session, whichever comes soonest.

Boxes containing vials with long expiry dates are stored at the back, and those with shorter expiry dates are at the front.

6.4.2  Loading a vaccine refrigerator

A vaccine refrigerator should be loaded as illustrated in Figure 6.12 and as described in Box 6.3.

Maximise

Figure 6.13  Storing vaccines in an ice-lined refrigerator. (Source: WHO, 2004, as in Figure 6.1, p.19).

6.4.3  Loading cold boxes and vaccine carriers

When you are loading vaccines into cold boxes and vaccine carriers before an immunization session, it is important to follow the steps in Box 6.4.

6.5  Maintaining the correct temperature of cold chain equipment

It is important to maintain the correct temperature in your cold chain equipment, and to adjust the temperature of your vaccine refrigerator if it is too high or too low.

6.5.1  Monitoring the temperature of your vaccine refrigerator

It is important to monitor the temperature of the main section of a refrigerator, so that you can ensure that it stays within the acceptable range for storage of vaccines.

To monitor the temperature of your refrigerator, you will need a thermometer and a temperature chart (see Figure 6.14), which you should tape to the outside of the refrigerator door. Then follow the steps in Box 6.5.

Maximise

Figure 6.14  Temperature chart, showing the safe temperature range and unsafe temperatures that require adjustment of the thermostat, or checking that the refrigerator is working properly. (Source: WHO, 2004, as in Figure 6.1, p.23)

When a temperature monitoring chart has been completed, replace it with a new one. Keep the completed charts in a record book for future reference. Action should be taken when the temperature goes out of the safe range, as illustrated in the example in Figure 6.14.

6.5.2  Adjusting the temperature of your vaccine refrigerator

The +2ºC to +8ºC safe margin may be difficult to maintain, especially for a kerosene refrigerator, so you should frequently check the condition of the vaccines. Here we give some guidelines on what to do if the temperature of your refrigerator becomes too low or too high.

6.5.3  Maintaining the correct temperature in cold boxes and vaccine carriers

It is just as important to maintain the correct temperature in cold boxes and vaccine carriers as it is in your refrigerator. To do this, you should follow the steps below:

• Place an adequate number of conditioned (melting) ice-packs or chilled water bottles in the cold box or vaccine carrier.
• Always place the cold box or vaccine carrier in the shade – never in a sunny place.
• Avoid opening the lid of your cold box or vaccine carrier except when you are removing a vaccine, and close it again immediately afterwards.
• Use the foam pad above the conditioned ice-packs to hold vials during immunization sessions.

6.6  How to maintain cold chain equipment

In this section we give some basic guidelines on how to maintain your cold chain equipment.

6.6.1  Maintaining vaccine refrigerators

A refrigerator works well only if it is properly installed, cleaned and defrosted (ice is removed) regularly. Thick ice in the freezer compartment does not keep a refrigerator cool. Instead, it makes the refrigerator work harder and uses more electricity, gas or kerosene. You should defrost the refrigerator when ice becomes more than 0.5 cm thick, or once a month, whichever comes first.

What to do when a vaccine refrigerator is out of order

If your vaccine refrigerator stops working, protecting the vaccines is the first priority. Move them to another cold place until the refrigerator is repaired. If you think that the problem will last only a short time, you may use a cold box or vaccine carrier lined with conditioned ice-packs or chilled water bottles for temporary storage. If the breakdown is likely to last a long time, you should move the vaccines to another refrigerator as quickly as possible — for example, by transporting them in a vaccine carrier to the nearest health centre.

When you have moved your vaccines to a safe place, check the electricity, gas or kerosene supply that keeps the refrigerator cold. If it is not working because the gas or kerosene has run out (Figure 6.15), try to get a new supply delivered as soon as possible. If the breakdown is due to a mechanical problem, try to repair the refrigerator if you can. If this is not possible, report the problem to the repair technician and your supervisor at the nearby health centre. Don’t forget to record the breakdown on the daily temperature recording chart.

Figure 6.15  A Health Extension Worker checks the kerosene tank of a kerosene refrigerator. (Photo: Janet Haresnape)

6.6.2  Maintaining cold boxes and vaccine carriers

• Always dry your vaccine carriers and cold boxes after use. If they are left wet with the lids closed, they will become mouldy. Mould may affect the seal of the cold boxes and vaccine carriers.
• Store your cold boxes and vaccine carriers with the lid open if possible, when they are not being used.
• Avoid placing cold boxes and vaccine carriers in the sun, as sunlight can cause cracks in their walls and the lids. If a cold box or vaccine carrier wall has a small crack you may be able to repair it with adhesive tape until you can get an undamaged one.

Summary of Study Session 6

In Study Session 6, you have learned that:

1. Vaccines should be stored carefully between +2ºC and +8ºC at all times, from the factory where they are manufactured until they are used. Excess heat or cold will reduce the vaccine potency (strength), increasing the risk that recipients will not be protected against vaccine-preventable diseases.
2. Health Posts should have a vaccine refrigerator and enough cold boxes and vaccine carriers to hold one month’s supply of vaccines and diluents, and one to two week’s reserve stock, to ensure that routine immunizations can continue if the refrigerator is temporarily out of working order.
3. Cold chain equipment, including refrigerators, cold boxes and vaccine carriers, must be loaded correctly to maintain the temperature of the vaccines and diluents inside. Ice-packs should be conditioned (allowed to begin to melt) before use in cold boxes and vaccine carriers.
4. Vaccines and diluents should be stored in the refrigerator compartment. If there is not enough space, diluents can be stored at room temperature, but they should be chilled to between +2ºC and +8ºC before use.
5. Freeze-sensitive vaccines (pentavalent, PCV10, TT and HepB) should be kept away from the freezing compartment, refrigeration plates, side linings or bottom linings of refrigerators, and frozen ice-packs.
6. A vaccine vial monitor (VVM) is a label that changes colour when the vaccine vial has been exposed to heat over a period of time. Before opening a vial, the status of the VVM must be checked to see whether the vaccine has been damaged by heat. Vials which have passed their discard point should be thrown away.
7. VVMs do not measure exposure to freezing temperatures. Inspect the freeze-indicator and use the shake test to make sure that freeze-sensitive vaccines have not been frozen.
8. A refrigerator works well only if it is properly installed, cleaned and defrosted (ice is removed) regularly.

Self-Assessment Questions (SAQs) for Study Session 6

Now that you have completed this study session, you can assess how well you have achieved its Learning Outcomes by answering the following questions. Write your answers in your Study Diary and discuss them with your Tutor at the next Study Support Meeting. You can check your answers with the Notes on the Self-Assessment Questions at the end of this Module.

SAQ 6.2 (tests Learning Outcomes 6.1, 6.2 and 6.3)

Figure 6.16 shows the VVM attached to two different vials of vaccine. Would you use the vaccines with the VVM shown below in (a) and (b)? Explain your answer.

Figure 6.16  Vaccine vial monitors (VVMs) for SAQ 6.2.

Answer

• a.The vaccine can be used because the inner square of the VVM is lighter than the outer circle. This means that the vaccine has not been damaged by excessive heat.
• b.This vaccine should not be used because the inner square of the VVM is almost as dark as the outer circle. This means that the vaccine has been damaged by excessive heat and should be discarded.

SAQ 6.5 (tests Learning Outcomes 6.2, 6.3, 6.4 and 6.6)

Figure 6.17 shows a dial thermometer used to measure the temperature of a vaccine refrigerator. Is this temperature safe for storing vaccines? What actions should be taken?

Figure 6.17  Refrigerator dial. (Photo: Basiro Davey)

Answer

The thermometer shows a temperature of +22^oC. This is much too high a temperature for storing vaccines! They have to be stored between +2^oC and +8^oC. This refrigerator is not working at all and must be repaired, or the power may have been cut off. Check the gas, electricity or kerosene supply, and call your supervisor to report the problem. Move the vaccines and diluents into cold boxes and transport them quickly to the nearest health centre for cold storage.