When discussing the impact of temperature on vaccines, heat is the better-known hazard. However, while the vaccine cold chain is a way to protect vaccines from inactivation associated with high temperatures, exposure to low temperatures can also result in potency losses. In a 2007 study, researchers found that vaccines were exposed to freezing temperatures in 14 to 35 percent of refrigerators or transport shipments. Thus, accidental freezing of vaccines poses a significant and growing threat to national immunization programs. And in locations where the equipment is not qualified or the process is not validated, the impact of environmental temperatures on the vaccines could be significant.
The common temperature range for the pharmaceutical industry is 2 to 8 °C, which hovers near enough to the freezing mark to make accidental freezing common. Many WHO prequalified vaccines, such as liquid formulations of aluminium-based vaccines against diphtheria, pertussis, tetanus, hepatitis B and Haemophilus influenzae type b, are sensitive to the effects of freezing. Freezing causes the vaccine to lose potency permanently. Vaccines damaged by freezing lose immunogenicity and become unable to provoke an immune response. Freeze-damaged vaccines are also more likely to cause sterile abscesses or other local reactions.
Many countries struggle with the growing threat of accidental vaccine freezing, which can pose a real risk for national immunization programs. In countries like Tunisia, the use of sub-standard domestic cold chain equipment instead of specially designed medical refrigerators compounds this threat.
In 2012, researchers conducted a demonstration project in Tunisia that investigated the effects of introducing various solutions to the problem. Their main finding was that combining new continuous temperature monitoring technologies and other interventions significantly reduced the incidence of accidental exposure to freezing temperatures, even with the use of underperforming domestic refrigerators. The scientists recorded cold chain storage improvements at regional, district and health center levels, as well as during transport legs across Kasserine in southeastern Tunisia.
Three main concerns led health officials to find a solution. First, in an effective vaccine management evaluation (EVM), a small-scale temperature monitoring study tested ten refrigerators used to store vaccines at district and local health centers and found that six had negative temperature excursions regularly. The EVM assessment showed that, while the temperatures were checked with standard thermometers twice daily as recommended, temperatures often dipped below freezing in certain refrigerators and remained below freezing for prolonged times.
The second concern was that Tunisian officials were equipping clinics and health facilities with domestic cold chain equipment purchased on the local market rather than purchasing pre-qualified, imported refrigerators; and rightly so as confidence in local products is a must. However, when it comes to vaccine storage there is no room for error. Laboratory testing showed that even the best-performing domestic models failed to meet WHO’s norms and standards.
Lastly, Tunisia hopes to introduce newer, more expensive vaccines, which are highly sensitive to freezing. Many developed and developing countries also hope to improve the quality of vaccines, so preventing vaccine freezing is essential.
Tunisian officials implemented a two-pronged approach to reduce accidental vaccine freezing in the cold chain in those same facilities as they had conducted baseline testing. They conducted the demonstration for six months, between March and September of 2012.
In the first approach, officials introduced the technology and practice of continuous temperature monitoring for both the storage and transport of vaccines. For the second approach, the officials introduced new high performance containers to transport vaccines. They also switched “Phase Change Material” (PCM) packs that stabilize temperatures.
Introducing these freeze prevention solutions decreased the number of times the temperature dropped below the 2°C recommended threshold. The number of freeze alarms at all levels decreased, and dropped by 40 percent at health centers. The researchers also noted that implementing the solutions reduced the risk of freezing during transport from 13.8 percent to 1.7 percent. It's important to note that the approach implemented in this demonstration project is not suitable for long-term use in domestic refrigerators which are used extensively in health centers and larger facilities.
I recently returned from an auditing visit to Africa and based on my findings I realize that the example of Tunisia is as relevant today as it was in 2012. Be it a developing country or an already developed country, adopting the practice of continuous temperature as a standard procedure can significantly reduce the risk for accidental freezing and strengthen cold chain equipment management to protect the potency of vaccines transported to people in difficult-to-access areas of the world. Additionally, by utilizing qualified equipment and validated processes it drastically improves the reliability of the chain of custody.
Are you thinking about your critical cold chain storage equipment? Are you making sure your equipment is designed, constructed and maintained to suit the operations to be carried out? To learn more about maintaining temperature throughout logistical activities, please read my eBook Cold Chain Qualification: 5 Questions You Must Ask When Shipping Biologics!