New Protein 'Burrito' Helps Keep Vaccines Stable Without Cold Storage

Much like perishable food products, vaccines—or, rather, the viral components that make them tick—can go bad if stored improperly. Researchers may have found a way to keep them from spoiling in hot environments, however.

In a study conducted at the University of Michigan, researchers found that subjecting whole inactivated viruses to a chemical process known as “coacervation” successfully insulated them from the fluctuations in temperature that can spell their doom. The October study was published in the journal Biomaterial Sciences. 

“Any improvement in the temperature stability of medicines would help to decrease the costs and improve the quality of life for people who have to deal with these types of therapeutics every day of their lives,” co-author Sarah Perry, PhD, associate professor in the department of chemical engineering at the University of Massachusetts, tells Verywell. 

Jere McBride, MS, PhD, a professor in the departments of pathology and microbiology and immunology in the University of Texas’s Medical Branch who was not involved in the study, is cautiously optimistic about the approach, although he clarifies that he is not an expert, per se, on vaccine development and storage. 

“Without specific knowledge on this approach, I think this method could be valuable in increasing access to vaccines by minimizing cold chain requirements, thus improving stability,” he says. 

Vaccines can only survive within a narrow temperature range, making them a major headache for laboratories to design, manufacturers to produce, and distributors to transport. At temperatures below 2°C, they freeze, sustaining physical damage that Perry compares to “being crushed, but on a molecular scale.” At temperatures above 8°C, they spoil like “a steak [left] out on the counter” as their proteins begin to denature—or “unfold.” 

“A key part of how vaccines work is that they teach our bodies how to recognize a particular infection," Perry says. "If the specific protein, or the overall protein capsid of the virus starts to unfold, the information we are trying to teach our immune system would be lost. For instance, we’ve heard a lot about this ‘spike protein’ for COVID-19. That protein has a very specific 3-D shape, and that is what we are trying to maintain."

By using this chemical process, Perry and her team found that that coacervation significantly increases vaccines’ temperature stability and, therefore, their longevity.

How Are Vaccines Currently Transported? 

Vaccines, as well as treatments for arthritis and multiple sclerosis, are currently transported via a “cold chain,” or a temperature-controlled supply chain that:

1. Begins with the cold storage unit at the manufacturing plant
2. Extends to the transport and delivery of the vaccine and proper storage at the provider facility
3. And ends with administration of the vaccine or treatment to the patient

However, cold chains are prone to malfunctions—so much so that around half of all vaccines produced each year end up in the trash, costing taxpayers money and individuals potentially life-saving immunity.

The cold chain must be maintained even after a home delivery, so people who require therapeutic treatments for specific medical problems must plan their days around their arrival. 

“This means that you have to schedule your life around being home to accept these shipments when they arrive," Perry says. "If a storm knocks out power to your house, you have to think about how you keep both your family and your medicine safe. If you want to travel, how can you bring your refrigerated medicine with you?”

The Bright Idea

Motivated by a desire to increase the storage tolerance of vaccines, Perry and her co-authors set out to find an alternative to the cold chain. They found a way to enclose viral particles within coacervates in a process known as “coacervation.” 

Coacervates are collections of macromolecules that are held together by electrostatic forces; Perry describes coacervation as “a type of liquid-phase separation.” For an example of a substance that relies on coacervation to work, you need to look no further than your bathroom vanity. 

“Shampoo actually works by undergoing this type of phase separation," Perry says. "The shampoo in the bottle is all one phase. However, when we put it onto our wet hair, we are diluting the concentration of the polymers and surfactants in the shampoo. Shampoos are formulated in such a way that this dilution is enough to cause phase separation to occur, allowing for the coacervate droplets to encapsulate and carry away dirt and oil."

Putting Coacervation To The Test

Once Perry and her co-authors had refined their methodology, they put it to the test—the test subjects being a non-enveloped porcine parvovirus (PPV) and an enveloped bovine viral diarrhea virus (BVDV).

They then compared the coacervated PPV and BVDV to free (meaning non-coacervated) PPV and BVDV. After one day at 60°C, the viral titer of coacervated PPV had remained steady while that of free PPV had declined somewhat. After seven days under 60°C, the viral titer of coacervated PPV had declined somewhat while that of free PPV had fallen off completely. 

In the study, Perry and her co-authors attributed the former’s “significant retention of activity” to encapsulation in the form of conservation. They hypothesized that coacervation may increase the temperature stability of vaccines by preventing protein denaturation, or protein unfolding. 

As for whether coacervation could potentially be used to increase the stability, and therefore the longevity, of the highly anticipated COVID-19 vaccine, Perry says that it’s theoretically possible. Unlike the vaccines in the study, however, the COVID-19 vaccine that is forthcoming from the pharmaceutical companies Pfizer and Moderna is based on COVID-19’s mRNA sequence rather than inactivated COVID-19 viruses. 

“Our recent work focused on viruses, so further study would be needed to understand how our approach could be applied to RNA-based vaccines,” she says.