What other criteria does CEPI use to consider the pros and cons of different vaccine candidates?
It’s very complex to weigh up what each individual candidate or platform can offer, in addition to preventing disease and potentially preventing transmission.
You might find that one vaccine works really well in 20-year-olds but doesn’t work so well in the elderly. So, we have to look at who we are trying to prevent disease in, and to make sure we have a portfolio of vaccines that can protect at-risk populations, which are diverse. You would ideally want a vaccine that can be used in pregnant women, and a vaccine that you might want to use in children, if needed – and that might be different from another vaccine. We should avoid giving the impression that one vaccine will provide the answer to everything.
And then there are other criteria we look at when we’re evaluating CEPI’s portfolio, such as manufacturing, and scalability. There’s also delivery – and the key point here of one-dose versus two-doses. The ideal would be a one-dose vaccine for a few reasons. One reason is faster protection: a single dose could be used potentially to control an outbreak as well as vaccinate people for general protection, whether they’re at significant risk or not. There’s also far more compliance with a single-dose regimen. And for vaccination campaigns, a single dose is far easier and far less expensive. In low-income and-middle-income countries, a single-dose campaign is likely to be more successful than a two-dose regimen. We’ve identified that’s a gap in our portfolio and we want to prioritise a single-dose regimen as one of our priorities.
And then, there’s the cold chain, which is important from an access perspective. Whether your vaccine needs to be stored at minus 70°C or 4°C are very different things. You’re adding a huge amount of complexity if you need to build a minus 70°C requirement into a cold chain. Obviously, we want to move those vaccine candidates forward with the best overall profile. I’d rather give a vaccine that’s at minus 70°C and 90% protective than one that can be stored at 2°C to 8°C but which is only 10% protective, as an example. You just have to weigh everything up together to get the best balance.
There’s a debate around the length of immunity. Does that complicate vaccine development?
This is a really important question. We are 6 months into the disease. So that’s the maximum data that we have at the moment. With respiratory diseases in particular, we do see waning antibodies. And we don’t know whether that waning of antibody will equate to loss of protection. We need to gather data to see whether people are being re-infected or not, and what the disease looks like, if they are re-infected. All of that information will help vaccine developers decide if booster doses of vaccine might be needed in the future, for example. So, it’s important that the work is being done. We need to follow it up in the longer term. We need to see how that waning of antibody from natural infection compares with waning antibody in vaccinated individuals, and continue to build on how best to use vaccines.