Scientists are working on two candidate vaccines that don’t need to be kept cool.

If the vaccines – which are made using viruses that normally affect plants and bacteria – prove safe and effective, they could make a huge difference, it is expected. Because the vaccines do not have to be kept refrigerated, it is a lot easier to spread them.


The researchers describe the candidate vaccines in the magazine Journal of the American Chemical Society. These are two vaccines with remarkable ingredients. For example, one vaccine was made using a virus that normally targets plants. And the other vaccine is made using a bacteriophage: a virus that infects bacteria.


Both vaccines are made in a similar way. The researchers infect plants and bacteria with the virus particles, after which the virus starts to multiply in the hosts. Millions of virus particles are thus obtained. These are then linked to a small piece of the spike protein that can be found on the outside of the coronavirus. In the eyes of our immune system, the end product resembles an infectious virus, but in reality the virus cannot infect animals and humans. Yet the immune system springs into action; it prepares an immune response that specifically targets the spike protein. And it’s that preparation that ensures that an actual run-up with the coronavirus goes mild or even symptom-free, or so it is hoped. The first experiments with mice are promising in that regard. Both candidate vaccines caused the animals to produce many SARS-CoV-2 neutralizing antibodies.


The candidate vaccines based on plant viruses and bacteriophages also have a number of major advantages. This means that they do not need to be stored and transported refrigerated. This is particularly good news for areas and regions that are difficult to access and where a (reliable) electricity network cannot be taken for granted. “What’s exciting about our vaccine technology is that it’s thermally stable,” said study researcher Nicole Steinmetz. “So we can also more easily reach areas where setting up ultra-cool freezers or driving trucks around with these freezers on board is not possible.”


But the fact that the candidate vaccines are not impressed by slightly higher temperatures has even more advantages. This means that they can also tolerate some heat during the production process. And that makes them very suitable for use in plasters filled with microneedles. To make such patches, the vaccines have to be fused with a polymer at high temperatures (nearly 100 degrees Celsius). That is no problem for these candidate vaccines. And such patches – which are pressed onto the skin, after which the vaccine is slowly and painlessly introduced into the body via the microneedles – once again make it easier to spread the vaccine, the researchers believe. Because, in principle, this method of administration does not require the involvement of a GGD employee or doctor; you can simply press the patch onto your arm yourself. “Imagine if you could send these vaccine patches by mail to the most vulnerable people, so they wouldn’t have to leave their homes and thus not be at risk of getting infected,” said researcher Jon Pokorski.


An additional advantage of this approach is that the vaccine – which is slowly absorbed by the body over a month – only needs to be administered once. “If clinics offer this one-time dose to people who are very difficult to get a second shot, then a larger part of the population would be fully protected and we have a better chance of slowing the spread of the virus. ,” says Pokorski.


But there is more that makes these vaccine candidates promising. For example, the experiments with mice show that the vaccines also protect against SARS: a coronavirus that was discovered in 2003 and caused several victims. It can be traced back to the pieces of the spike protein that the researchers incorporated in their vaccine. One of those pieces from SARS-CoV-2 is almost identical to a part of the original SARS virus. “It gives us hope for a potential pan-coronavirus vaccine that will protect against future pandemics,” said study researcher Matthew Shin.


To top it off, this part of the SARS-CoV-2 virus has not yet been affected by the mutations known to us that the virus has undergone. It suggests that the candidate vaccines work equally well against all variants. Whether this is really the case is currently being investigated.

The corona vaccines that are now being administered also contain a piece of the spike protein. However, they all use pieces that come from the ‘binding region’, ie the part of the spike protein that actually binds to our cells. And in that region many mutations take place. For the new candidate vaccines, the researchers chose pieces of spike protein from a region that does not bind directly to our cells and is less sensitive to mutations.

As promising as the vaccines are; its application is still a long way off. It has yet to be demonstrated that they are also effective and safe in humans. And such clinical trials take time. Whether the vaccines will make a difference in this pandemic remains to be seen. But even if they are late in the fight against SARS-CoV-2, the work has not been in vain, Steinmetz emphasizes. “This technology (…) can be quickly adapted to the next threat, the next virus X. We use the same nanoparticles, the same polymers, the same equipment and the same chemical processes to bring it all together . The only variable is the antigen (the piece of the virus, ed.) that we attach to the surface.”