Researchers have successfully vaccinated mice against flu and Covid-19 without using a needle.
Messenger RNA vaccines give our cells temporary instructions to make a protein recognized by the immune system. The immune system then learns to defend itself against the virus. In conventional vaccines, the RNA is carried in tiny fatty particles that protect it and help it enter cells.
Syringe.
Pixabay illustrative image
A team of American and Japanese researchers tested another method. It uses a device that propels a very small amount of liquid into the skin with a pressurized jet. No needle is needed: the speed of the liquid allows it to pass through the skin's surface.
The team also chose to do without the fatty particles that normally surround messenger RNA. This simplifies preparation but creates a challenge: when injected alone, this RNA triggers an immune response that is too weak. The researchers therefore looked for a way to help the body react more strongly.
They added two substances that stimulate the immune defenses, called adjuvants. One is based on aluminum phosphate; the other contains short DNA fragments. Separately, they provided little improvement. Together, they significantly strengthened the immune response in the mice.
To assess protection, the researchers vaccinated mice and then exposed them to the coronavirus responsible for Covid-19 or to the flu virus. In tests conducted on their lungs, the amount of virus still capable of infecting cells fell below the detection threshold after three vaccine doses.
This is an encouraging result, but it should be interpreted cautiously. Failing to detect infectious virus in a sample does not mean that every animal is completely free of the virus.
The researchers also compared inflammatory reactions with those caused by certain experimental preparations using fatty particles. Their method caused fewer reactions in these trials, but this is not enough to prove that it will be better tolerated in humans.
This needle-free vaccination therefore remains experimental. Before considering trials in people, its effectiveness and dosage will need to be assessed in other animals, among other things. The discovery mainly shows that there is another way to deliver messenger RNA.