A dose of the vaccine is in two delivery devices: the nose and mouth (what’s known as nasal spray vaccines). The antigen in each is tagged on the antigen membrane, and an accompanying particle is released on the end of a syringe. As the molecules are able to stick to both sides of the membrane, it’s possible for them to travel from one end of the syringe to the other, making it harder for the immune system to distinguish them.
The 2,000 Americans who are said to have developed the form of polio that makes them weep are in a population that is large and mostly healthy.
A standard dose of the vaccine, manufactured by Novartis, goes into a syringe and is injected into the muscle. The virus is supposed to fly out through the top of the needle tip and onto the vaccine in the muscle. The general assumption is that virus particles that resemble polio particles will survive the journey, while the rest of the vaccine particles will be killed off.
Using a vaccine that is delivered nasally is also more convenient, but it will be argued that it increases the risk of side effects.
What’s more, there is a vaccine that has had a version designed to be delivered in nasal droplets delivered via inhalation: Gardasil (previously known as the Gardasil 9 vaccine). It contains a protein that mimics the one in the target vaccine’s outer shell, allowing the body to better recognise it and hone its immune system in on it.
A small-scale study carried out by researchers at GlaxoSmithKline found that Gardasil delivered in the nose before a series of six throat swabs had a 40% reduced sensitivity to the antigens, bringing it up to about the level of normal.
But the main worry is around the delivery device itself. As these are often made from cell membrane-encapsulated materials, they are susceptible to bacterial contamination. In one case of an earlier version of the vaccine given in the nasal route of administration, in Washington state, up to seven people became infected with the enterovirus (EV-D68) in 2013.
More recently, clinical trial data reported in the journal Pediatrics showed a small but increased risk of EV-D68 infection in the group given the oral vaccine in the US.
Experts think that the vaccine works by provoking antibodies, meaning that too many bacteria will easily be cleared by an immune system.
With more details of the substance included in the multiple doses of this vaccine, a more concentrated strain and immune response would be expected.