When most of us think of vaccines we have visions of a nurse with a sharp needle, approaching a bared forearm. Although this is the most conventional means of administration, there is a variety to choose from, with different effects and efficacies. In this article we explore some of the methods of delivering vaccines.
Injected
- Intramuscular: many vaccines are injected into muscle tissue – such as the upper arm or thigh. Muscles contain many blood vessels so that the vaccine is quickly distributed into circulation. The benefits include limited side effects although thy should be administered by trained healthcare professionals to reduce damage to nerves or blood vessels.
- Subcutaneous: a few vaccines are injected into a layer of fat beneath the skin, which has fewer blood vessels than the muscle. This results in a slower, more constant release, ideal for the delivery of some live attenuated vaccines and inactivated vaccines. These are ideal for self-administration often in the abdomen or thigh.
- Intradermal: currently mostly used for allergy testing but also for the administration of rabies and tuberculosis (BCG) vaccines. This method is useful because the skin contains many immune cells and could therefore be more efficient – less of the vaccine might be needed, meaning more doses for more people! However, the skin is so thin that these injections are generally administered by trained health professionals.
- Intravenous: occasionally medicines are delivered directly into the veins, a speedy and effective method of distribution. Vaccines haven’t generally been administered this way, but initial evidence suggests that the tuberculosis and malaria vaccines might be more effective. Once again, hitting the right spot is a tricky task, so we rely on trained healthcare professionals to do this!
- Injections often cause pain and concern among patients, which leads to vaccine fear or hesitancy. Another issue is the risk of injury or contamination through reuse, as well as short supply.
Oral
- Oral vaccines are swallowed, great for people who are afraid of injections. A 2021 poll by Vaxart revealed that nearly 19 million Americans who did not want an injectable vaccine would receive the oral dose.
- Easier to manufacture and administer, they can be delivered by people without specific training, so they have greater distribution potential.
- Oral vaccines are encountered by immune cells in the mucosa as well as those in the bodily fluids. They are therefore effective in protecting against gut infections like cholera and polio as pathogens must cross the mucosa to infect the gut.
- Unfortunately, only a few vaccines are licensed for oral administration, including the polio vaccine. This is because the vaccine passes through the gastrointestinal conditions and must be able to avoid the mucosal tolerance – this stops our immune systems from responding to antigens that we consume in food.
Mucosal
- Mucosal sites include oral, nasal, ocular, rectal, and vaginal.
- These are particularly effective in epidemics of infections that are transmitted mucosally.
- The cost of producing and delivering these vaccines is lower and purity is not as critical as it is for injected vaccines.
Patch
- The Vaccine-containing Mircoarray Patch (VMAP) is an intradermal technique. UNICEF is currently pushing for further research and development of these vaccines because they increase accessibility and ease administration.
- They arrive ready to administer and will likely be more stable at a wider range of temperatures. They can be delivered by health workers with very little training, meaning greater uptake in areas that previously presented vaccine challenges.
- PATH suggests that “true vaccine equity” can be achieved through investment into a range of formulation technologies, of which the patch might be one.
- The need for needles is eliminated, waste is reduced, and storage and transport become easier. However, there is a need to ensure market incentives by vaccine manufacturers as the cost is likely to be higher until offset through delivery.
Book your World Vaccine Congress tickets to Barcelona in October 2022 to hear Dr Sean Tucker of Vaxart discussing oral vaccine administration here.
