The success of Covid vaccines has led to deaths and severe disease in countries that have them, even as the virus evolved to sidestep immunity and rip through populations more swiftly.

The rapid development of Covid shots is the best achievement of the Pandemic. In a small number of labs around the world, teams are taking on a problem that cannot be ignored: that the virus remains rampant in the face of mass immunity.

The problem has arisen because existing Covid vaccines are better at preparing the immune system to fight the virus inside the body than stopping it at the gates. Even though immunity has largely been defanged, countries still face waves of infections that hospitalise vulnerable people, keep staff off work, and leave an uncertain proportion of people with long Covid.

Hopes to stop the spread of infections are dependent on the development of vaccines that are delivered by spray up the nose rather than a shot in the arm. They want to protect the nose and throat from Covid infections. People who don't like needles may be more willing to use the sprays.

If you think of your body as a castle, you should get a vaccine to protect it from invaders, according to the medical director of the Co.

If you train your immune system to work at the gates of the castle, the invaders will have a hard time getting in.

A vaccine made in a similar way to seasonal flu vaccines could be churned out by the same facilities, meaning it could improve global access to Covid vaccines.

There are more than a dozen clinical trials of Covid vaccines under way. The immune response in the nose should be strong for an vaccine to work. It helps if people don't swallow or sneeze it, which can make it difficult to get the correct dose.

Pfizer and Moderna vaccines do not work immediately for delivery in thenasal space. Both vaccines use small particles to get the genetic instructions for the coronaviruses into the cells.

In theory, RNA vaccines could work, but nobody has worked out how to deliver them as an effective spray.

It is more of an engineering problem to get the lipids across the mucus and into the cells, since they are delicate and work beautifully when you inject them into the body.

Only one vaccine has found a wide market so far, and that is the one marketed as Flumist in the US and Fluenz in Europe. The vaccine can cause an immune reaction if it gets into the cells of the nasal lining. It helps to reduce community by protecting the individual against flu infections.

Results from an early-stage trial of the Oxford/AstraZeneca vaccine are expected soon. The weakened adenoviruses used in the Oxford vaccine may be able to induce an immune response in the nose. The strength of the immune response, how protective it will be, and how long it will last are some of the hurdles that researchers face. It is best to top up Covid jabs that provide more enduring protection against severe disease if you want an autumn booster.

Prof Peter Openshaw, a member of the government's New and Emerging, said that the systemic vaccine is important for protecting against severe disease.

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Sandy Douglas, a pharmaceutical physician who works on the Oxford vaccine, doesn't expect any Covid vaccines to be available this year.

This is one of the most important questions in vaccinology, not just for Covid, but for the next Pandemic. As soon as possible, we need to solve that problem. It may take a lot of effort and investment, but it is worth it. If we had vaccines that stopped the spread of the disease, we could see how big the advantage would be.