Before there were any cold chain studies in Europe, people had always attributed some cold chain failures such as spoiled products to the inaccuracies in management and logistics and not to the climate. 

It was previously assumed that a temperate climate contributed less harm to cold chain products as they had a generally colder climate than their tropical counterparts. But it turned out not to be the case as proven by a study in 1987 and 1988. It was found that temperate climate provided instability like the ambient temperature of the generally warmer tropical region.  

Study of Cold Chain in Temperate Climate

study of cold chain in temperate climate

There have been several cold chain monitoring studies conducted after 1988. But the study done in Hungary was the pioneer not just in Europe but also on a global scale. 

Cold chain is an umbrella term that includes a lot of temperature-controlled products in the supply chain. Vaccines comprise the majority of these products. The researchers focused on these products as they were not only necessary across all points of the world, but they also ranked high on the temperature-sensitivity scale. 

At the time, immunization programs were rampant and flourishing in Europe. But their path to efficiency was just starting to take flight. Technologies were not as cutting edge as they are today where its advancement could shelve a large part of spoiled products at the time of the study. Nevertheless, Europe was at the onset of big immunization improvements.

At the heart of Europe lies a small but industrialized and developed country of Hungary. Which means if there were any problems related to product spoilage, logistics and management infrastructure would be the least option to blame. But since ineffective and unstable products form part of the minority of their cold chain result, managers started to look for other factors contributing to a big chunk of product loss. That’s where the issue of ambient temperature was considered. 

Hungary is located in the global temperate zones, like Poland, Ukraine, and much of Northern Europe. Which means they experience a very hot summer and a very cold winter. The extremeness of both climates results in an imbalance of ambient temperature that is less conducive to cool cargos including vaccines. 

Hungary was chosen because of the reasons above. Apart from their physical capacity and environmental situations, they also had an extensive vaccination program. Their immunization campaigns were managed by well-interconnected health centers. Atop the organizational chain was the ministry of Health located in the capital. It managed a comprehensive public health headquarters that covered 19 counties of the country. Overall, they had 162 district public health services (DPHS), and within the districts, there are 3300 child health centers (CHC) with preventive and curative sections. The preventive section was responsible for the immunizations. 

In partnership with the World Health Organization (WHO), the Hungarian Ministry of Health focused on four vaccines as part of their routine immunization programs: the triple Diptheria, Pertussis, and Tetanus (DPT) vaccines, and Measles Vaccines. The DPT was manufactured and distributed within the country while Measles vaccines were coming from Moscow. 

Those are the vaccines included in the cold chain studies. All of them are temperature sensitive, both to heat and cold, as all vaccines are. Thus they are very good subjects of the study as their instability to temperate environments of the country could very well provide the information needed for the storage and distribution of all other vaccines within and outside the country. 

What Tests Were Performed?

At that time there’s very little technology to measure cumulative heat exposure. While the market now is flooded with different devices of those kinds, the only instrument available and the most effective in the 1980s was the cold chain monitor (CCM) device. 

This is a kind of card accoutered with a tube that indicates the cumulative heat exposure by showing blue-filled parts. This indicator changes irreversibly from white to blue if exposed to temperatures higher than 10°C (50°F) and 34°C (93°F). This is used to monitor conditions of temperature-sensitive products in transit and in storage.

When a vaccine is exposed to temperatures that are too high, its accompanying CCM will gradually shift color starting from A to D. Every letter has its corresponding degree of temperatures. When it reached letter D, that means the product was subjected to temperatures as high as 34°C (93°F). That could already be damaging to most vaccines so they still need to be tested if exposed. Health workers use this device as an effective estimation of the length of time that vaccines were left out in high temperatures. BCG, DPT, polio and measles vaccines all use CCMs. 

The study was done twice. First, in the summer of July to September of 1987 and the next is in  the winter between January and March of 1988. Two opposing climates were chosen because a normal climate was seen as amicable to cool cargos. Winter and summer are inherently risky so they were chosen as the timeframe. 

The first half of the study was conducted in Fejer, Gyor-Sopron, and Szabolcs-Szatmar counties. The other half was in all three and Pest, Nograd, and Csongrad counties. They were chosen because of their distance from each other and the main health center. All the patients were chosen randomly among the counties.

The research aimed to measure four  criteria:

  1. Exposures to adverse temperatures and delays in distribution
  2. Places where such exposure or delay occurred 
  3. Percentage of vaccines at risk of deterioration because of such exposure or delay (actual and predicted)
  4. The performance of refrigerators of different types. 

Results of Test

This first cold chain study had informed the ministry of health as well as the WHO on the aspect of cold chain in Europe that needs improvement. One of them is the temperate climate factor. 

The advent of cold chain monitor has given opportunities for cold chain managers and health facilities to strengthen their immunization programs even in developed countries. 

While the ongoing immunization programs in Hungary before the study was in accordance with the WHO guidelines, the study exposed the weaker links of the chain.Afterwards, there was more investment  poured down on better storage and packaging technologies upon learning that the extreme temperatures provided an unsafe factor to vaccines. 

In particular, these are the results of the study:

  • All the vaccines included in the study have been exposed to high temperatures. And there was a high possibility that that exposure led to a loss of potency. DPT was also damaged to freezing temperatures but not the other vaccines. 
  • Both BCG and DPT vaccines are subjected to delays and exposures to extreme temperatures both of which contributed to their slow deterioration. 
  • The refrigerators might have been the best at that time but they did not ensure safe storage. Hence, they cannot be trusted to protect vaccines at all times. 
  • Because vaccines, especially measles, are stored for too long in immunization programs, they had higher risks of degradation. Storing and packaging technologies used couldn’t keep the healthiness of the vaccines for such a long duration. Or even if it could, a small percentage might have been disposed of.
  • Detailed analysis showed that the varying locations in the study had contributed to the results differently. Some counties were too cold or too hot or that one had better health personnel over the other. But the best and the worst-performing counties had a wide margin of variation. Meaning that the way they handled the vaccines were not as collaborative as today.

Other Studies

Succeeding studies had solidified the notion that a temperate climate could be just as damaging as a tropical climate. If not carefully considered, meaning the proper measures in logistics and management are not taken, then the ambient temperatures can get the better off the vaccines. 

In North America, the impact of winter months on vaccines was studied. As the study in 1987 and 1988, the materials used were the cold chain monitoring as well as other advanced devices of the time. 

The study focused on the traditional cold chain where they kept vaccines between 2°C (35°F) to 8°C (46°F). During storage, the vaccines were in good condition, but temperatures started to vary when the products were moved from 3PL to service points. A wider variation of temperatures was found in the service points. High-temperature excursions were observed for short periods of time while exposures to freezing temperatures were more both higher in number and duration. 

Final Thoughts

The study in Hungary has paved the way for more advanced and comprehensive studies regarding the ambient temperature of the vaccines. While the world has already known that a tropical climate poses more risk to temperature-sensitive products, the study has shed light on a  topic not so talked about: the impact of temperate climate on vaccines. Years after the studies, the global cold chain management has improved quite well, developing devices that could further isolate the vaccines from their ambient climate and prolong a stable cold life. 


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