Inspired by breath strips, scientists break away from needing a ‘cold chain’ to deliver vaccines

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One of the many challenges in developing and delivering vaccines where they are needed is keeping them at the right temperature at the right price. Most vaccines, especially ones made from weakened forms of living viruses, must be kept cold to be effective.

Scientists have tried many strategies to get around the need for a “cold chain” from supplier to patient, but their workarounds don’t fit the often hot climates in developing countries where threats like Ebola have emerged.

Carlos Filipe and his colleagues from McMaster University offer an affordable, durable solution that protects vaccines without keeping them cold: mixing dried vaccines with a sugary combination that stays stable at temperatures up to 40 degrees Celsius. They tested their approach on flu and herpes simplex 2, two envelope viruses that are more sensitive to thermal degradation. Their experiments were in lab dishes and in mice, but not in people. 

Here’s what Filipe said about his team’s work, published Tuesday in Scientific Reports. This interview has been condensed and lightly edited.

Why did you decide to look at this problem?

Five or six years ago we were working on the development of sensors for detecting some pesticides in water and in food and soil and it was necessary to use an enzyme to perform the assay. The enzyme was thermally unstable. On a trip to the supermarket, one of my grad students saw these Listerine breath strips. That film dissolves very quickly and it’s made of a sugar called pullulan. We knew there were some sugars that have the ability to stabilize thermally some biomolecules, like proteins and antibodies and so on. That’s where it started. We just bought this material pullulan, which is available at industrial scale. You make a solution of it and allow the enzyme to dry into a film. Instead of a Listerine strip, now you have a film that contains the enzyme.

We put the enzyme on the film, starting at 90 degrees [Celsius], for a long period of time and we saw it was protected from thermal degradation. That motivated us to say, OK, can we do this with a bacteriophage so that we can create this film to have the ability to kill bacteria specifically? We were able to show that that is the case, so we keep pushing and pushing until the final goal was to do it with vaccines.

When we saw the results with the enzyme, it immediately planted a seed in our mind that our ultimate goal would be to do the work with vaccines, but it took us some time.

What came next for vaccines?

We figured out we needed to add a second sugar, which is called trehalose. Trehalose and pullulan are made by the same manufacturer in Japan. If you can buy a Listerine strip in the supermarket, it means that it’s industrially available and it’s very, very cheap. And FDA-approved.

How do you protect vaccines with them?

You take a vaccine that is already developed — we don’t want to develop any new vaccines because you need an additional approval process. So you have that vaccine in liquid form, you just add pullulan powder and trehalose powder, and you let it dry, and that is it.

You make it sound so easy.

No, it is really that easy.

How long do they stay stable?

For the vaccines, we start them at 40 degrees [Celsius] for three months and it has full potency. With enzymes, we kept enzymes for more than a year at room temperature, all these enzymes people use for molecular biology like polymerases, restriction enzymes. We are also able to preserve those at room temperature.

How, then, would the vaccines be given to people?

If the vaccine is to be injected, then water or saline can be added to the film and it will dissolve in a matter of few seconds. The same reconstituted liquid can be used for mucosal delivery — for example, as a nasal spray.

What needs to happen to try it in the field?

The technical solution is the simplest part of the problem because it is cheap, it is simple, the ingredients are FDA-approved. But one has to think that there is already infrastructure in place to deploy these vaccines. There is a cold chain and this type of reformulation will require some investment from companies.

I have to be pragmatic — I don’t know if there is a lot of appetite for this type of investment. We’ll try to engage with some NGOs and we’ve also submitted a proposal to the Gates Foundation because I think we need a strong partner to make these be deployed. I don’t know if there is going to be a lot of motivation to push this kind of technology.

It will be nice if you can increase the availability of vaccines in very remote areas of the world.