The potential for giving the wrong dosage of the Pfizer vaccine is a well-known risk authorities should have been prepared for, a vaccination expert says.
Key points:
- Nearly all vaccines used before now in Australia have come in single-dose vials
- One expert said the risk had to be weighed against the urgent need to get jabs into people's arms
- Similar excessive dosing errors have happened in Israel and Germany
Two elderly residents of a Queensland aged care home were given a higher than recommended dose of the new mRNA vaccine during the first phase of the vaccine rollout, which kicked off on Sunday.
The incident happened on Monday and the two patients, aged 88 and 94, were given up to four times the recommended dose.
They were monitored afterwards and appeared to have no side effects, with carers continuing to keep them under observation on Thursday.
The Pfizer vaccine comes in multi-dose vials. Each vial contains enough vaccine to vaccinate five people — or six, with a special low-waste syringe.
Jim Buttery, an infectious diseases physician and vaccinologist, said the potential for giving too much vaccine from the multi-dose vials was a well-documented risk that vaccine manufacturers knew about and authorities would have prepared for.
It was a particular risk in Australia, he said, because almost every vaccine approved for use in the country before now was a single-dose vaccine.
The only exception was the tuberculosis jab, which was not commonly used.
"Multi-dose vaccines and vaccines that need to be reconstituted are more likely to have errors associated with their administration," Professor Buttery said.
"The manufacturer knew this, but in context, when they have those discussions, they have to weigh it in terms of risk versus error versus efficacy and speed."
The doctor involved had not done the required training. He has been stood down from the program and reported to the federal regulator.
"I think it's critical that everyone who administers these vaccines has the appropriate training, both for vaccines in general, and this vaccine in particular," Professor Buttery said.
Similar errors have been reported in Israel and Germany
Excessive dosing involving Pfizer's multi-dose vial has also been documented in overseas rollouts.
In December, eight healthcare workers in Stralsund, Germany were each given an entire vial.
Four developed flu-like symptoms and were taken to hospital with fever but later discharged.
The others didn't show any symptoms and were sent home.
In Israel, the same error happened in December and again January.
Three people received five doses of Pfizer in the one injection at the same medical centre. They were taken to hospital for monitoring but showed no effects.
Israeli Immunological Society president Amiram Ariel told the ABC the errors occurred because of "inexperience" at the beginning of the country's large scale rollout, and later "fatigue" as the country moved through millions of patients.
"The major problem is the fact you have to dilute the vaccine before you inject it," Professor Ariel said.
"In these cases the practitioners are forgetting to do the dilution and injecting the vaccine concentrate as it is.
"The medical staff are exhausted from treating this pandemic with all the waves. [In Israel] we have gone through a third wave already. And when you're doing a very rapid vaccination protocol in a short time that would also affect some people doing it in late hours."
Professor Ariel said there was no alternative but to use a multi-dose vial of the Pfizer jab.
"Due to the intensive protocol of vaccination in Israel the training period had to be really short because you were injecting a lot of people in a short time," he added.
What is the risk from too much vaccine?
According to Professor Buttery, the main risk is a higher chance of localised reactions like tenderness and swelling and what experts call "systemic reactions" such as muscle aches and pains
He said an excessive dose would not be life-threatening and would not lead to the patient developing COVID-19, because the inoculation does not contain live coronavirus.
"[Also] with the COVID vaccine the risk of adverse events is lower in the elderly than young people because the immune system of older people doesn't react as strongly," he said.
Pfizer conducted trials experimenting with larger doses and saw no impact on subjects.
But it declined to reveal specific information on the trials after a request from the ABC.
The company said it was working with the federal Health Department and the Therapeutic Goods Administration to ensure the vaccine was used safely, and said the federal government provided vaccinators with mandatory training materials.
Questions remain about whether dosage errors can impact a vaccine's effectiveness.
The Pfizer vaccine has been designed to be given in two doses, with the first to start building immunity, and the second to reinforce it.
Professor Buttery said an excessive dose of the vaccine was unlikely to reduce effectiveness, but it didn't improve it either.
"Typically as part of the vaccine's development they give a different range of dosages and come up with the lowest dose possible," he said.
Speaking on the Queensland incident, Professor Buttery said the fact that a nurse involved identified the error was a testament to the checks and balances in place.
The Department of Health is continuing its investigation into the matter.
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2021-02-25 01:06:36Z
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