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ScienceNovember 17, 2021

Siouxsie Wiles: What you should know about ‘adverse events’

Image: Getty Images
Image: Getty Images

Thousands of reactions and other medical events following vaccination have been reported to Medsafe so far. How concerned should we be?

A few days ago, I heard my first cicada of the season, a clear sign that summer and Christmas are just around the corner. In fact, Christmas day is just a little over five weeks away. Five weeks! To safely enjoy all the holiday season has to offer, one of our best protections is for all of us who are eligible to be vaccinated and to be at least two weeks out from our second dose. That means if someone hasn’t had their first dose yet but get it by this Friday, and then get their second dose three weeks later, they’ll be fully immunised just in time for Christmas day.

I’ve heard from a few people who are still hesitant about being vaccinated that one of their worries is the data about “adverse events” that is publicly available on the web. As a way of continually investigating the safety of vaccines, regulators around the world have systems for both health professionals and the public to log things that happen to anyone in the hours, days, weeks, or months after they’ve been vaccinated. In the spirit of transparency, that raw data is made available for the public to see.

In the US, the system is called VAERS which stands for Vaccine Adverse Event Reporting System. Here in Aotearoa, Medsafe, our medicines and medical devices safety authority, contracts the Centre for Adverse Reactions Monitoring (CARM) in Dunedin to collect voluntary reports of adverse reactions – not just to vaccines, but to medicines, herbal products, dietary supplements and blood products. Medsafe then collates the reports related to the Pfizer Covid-19 vaccine and puts these on their website each week. They appear there as AEFI, which stands for “adverse events following immunisation”.

These reporting systems are very important but as we’ve seen during the pandemic, they are wide open to being abused by those pushing an anti-vaccine agenda. Here is what you need to know about the data available on these websites.

What’s an AEFI?

The Medsafe website defines an AEFI as “an untoward medical event which follows immunisation and does not necessarily have a causal relationship with the administration of the vaccine. The adverse event may be an unfavourable or unintended sign, abnormal laboratory finding, symptom or disease.”

‘Causal relationship’?

Before I explain the adverse events that have been reported in New Zealand so far, lets unpack that “causal relationship” bit. We are rolling out the biggest vaccination campaign in history. Thousands of people are being vaccinated every day. It’s also a fact that bad things happen to people all the time. The sad reality is that every day someone somewhere is having a heart attack, or a stroke, or a seizure, or a miscarriage. Every day people die. What we need to know is, did getting vaccinated put them at any higher risk of that happening, or was the timing purely a coincidence?

That’s what Medsafe mean by the data not necessarily reflecting a causal relationship between vaccination and the adverse event being reported. We also have to remember that because anyone can report an adverse event sometimes rather spurious things get reported. A good example is one overseas database having a report of someone being struck by lightning. That’s hardly going to be caused by being vaccinated! Still, only about a third of reports to Medsafe are from the patient, with many of the others coming from the vaccinator, nurse, GP or pharmacist.

To understand whether there is a relationship between the adverse event and vaccination, experts examine the data, looking for signals that something is happening more frequently than we would expect, or perhaps in different people to those we would normally expect it to happen to.

What AEFI have been reported for New Zealand so far?

The data currently on the Medsafe website is up to and including 23 October 2021. In that time, over 6.6 million doses of the Pfizer vaccine have been administered here. From those 6.6 million doses, there have been 32,372 AEFI reports. So that’s well over 6.5 million vaccine doses administered with no adverse events reported.

The overwhelming majority of AEFIs reported to date are classed as non-serious. The 10 most frequently reported adverse events in order are dizziness, headache, pain at the injection site, lethargy, nausea, chest discomfort, influenza-like illness, fever, fainting and numbness.

What about serious adverse events?

Medsafe defines an AEFI as serious if it meets any of the following criteria: it is a medically important event or reaction; it requires hospitalisation or prolongs an existing hospitalisation; it causes persistent or significant disability or incapacity; it is life threatening; it causes a congenital anomaly/birth defect; or it results in death.

From the over 6.6. million Pfizer doses administered up to and including 23 October 2021, there have been 1,125 AEFI reports that were considered serious. This includes 94 deaths, of which 41 were unlikely to be related to the vaccine and 42 could not be assessed as there was not enough information provided. Ten cases are still under investigation, and one death is reported as likely due to vaccination.

The other serious AEFI are provided in a table, and include 13 cases of Guillain-Barré Syndrome, 36 heart attacks, 69 strokes, 67 cases of deep vein thrombosis, and 15 miscarriages.

Putting the AEFI data in context

What do those numbers mean though? How many people have a heart attack or stroke each day? That data is hard to find easily, but heart attacks and strokes are often classed together as the result of what’s called cardiovascular disease. According to the Heart Research Institute of NZ, 16 people a day die from cardiovascular disease in New Zealand. When we look at Guillain-Barré syndrome, which is a rare disorder of the nervous system, that is thought to affect between 40 and 80 people in New Zealander each year. It’s estimated that one in every 1,200 people will develop a deep vein thrombosis each year. And as for miscarriages? It’s estimated that one to two of every 10 pregnancies end in miscarriage. That’s several a day.

I wish Medsafe would include data on how often people experience the types of serious adverse events listed when we aren’t busy vaccinating thousands of people every day. That would help out the data reported in context and would immediately help address many people’s anxiety about getting vaccinated.

Keep going!