Improving vaccine allergy tests

A team of South Australian researchers has been studying ways to improve tests for allergies to vaccine ingredients.

With doctors often recommending pre-vaccine allergy tests for people who are prone to allergic reactions, the team, led by Alexander Troelnikov of SA Pathology and Griffith Perkins of the University of Adelaide, identified a component of the Pfizer vaccine, which has a higher incidence of allergic reactions, that could be used to recognise potential allergies.

The Pfizer vaccine against COVID-19 is a new type of vaccine that uses mRNA to prime the immune system against SARS-CoV-2, but there is a slightly higher incidence of allergic reaction to it than expected in a normal population.

The team found that allergic reactions may not be to the mRNA, but to another component of the vaccine that helps deliver the mRNA. It’s information that might help improve the pre-screening tests.

“If you have anybody that we think is likely to have a bad reaction to the vaccine, what you do is you invite them into their specialty clinic and you prick their skin with it,” says Perkins.

These skin prick tests contain only a tiny amount of the vaccine so that any reaction is small and generally localised to irritated skin.

“If they don’t [have any reaction], you can also inject a little bit of a vaccine underneath their skin and see if they have a reaction to that as well,” says Perkins.

“But what’s recommended internationally is not using the vaccine, because most people can’t get access to the vaccine.

“What you need to do is protect the [mRNA] capsule from being cleared by the immune system, so they put these long polymers on it – they’re called polyethylene glycol polymers.

“We sort of thought that polyethylene glycol, out of anything in there, could be a potential allergen to people.”

The next step was to see whether polyethylene glycol could be used to conduct the allergy tests instead of the vaccine, but the form of the molecule was crucial to whether the test would give results.

“What we found was that it wasn’t good enough to test people with just the polyethylene glycol containing drugs,” says Perkins. “It was with polyethylene glycol as it was on the vaccine that causes your response in the skin.”

This is a bit different to other types of allergies, where a reaction will often happen no matter the form of the allergen.

“It’s a weird allergy,” says Perkins. “So usually, you would have allergies to proteins. And they all work very nicely; you get quite consistent results.

“With polyethylene glycol, it’s a polymer, so we think it is not very good at inducing a reaction, rather than just floating around in its free form.

“[But] when you have it presented nicely on the nanoparticle, we think that it actually induces the reaction better.”

Perkins explains that this information may help inform the design of the test, so that there’s no need to prick the skin and cause a reaction. Instead, a blood sample could be taken and tested in the laboratory.

Beyond this, nanoparticle delivery systems may be used in other types of medication and treatments, so designing tests to identify allergies to polyethylene glycol could be used for these types of medicines, too. 

The study, published in The Journal of Allergy and Clinical Immunology, involved only a small sample of people who presented a reaction to the Pfizer vaccine, but looked at chemical ways of improving diagnostic allergy tests.

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