A small number of people are reporting side effects after getting the Covid-19 vaccine. Mirjam Guesgen explains what they entail, and why they are no cause to be alarmed or hesitate before getting vaccinated. 

How many people in New Zealand are getting side effects from the vaccine?

TLDR: Not many. The best way we have to measure this is via the Centre for Adverse Reactions Monitoring database. It collects information on “adverse events” after immunisation.

Adverse events?

Adverse events aren’t necessarily the same as side effects. People getting immunised file these reports themselves if they suspect the vaccine caused something like a headache, pain or fever (an event) or if something weird shows up in their bloodwork for example.

That doesn’t mean the vaccine caused it, just that it happened after getting a jab.

Up to 10 May, there were a little over 2,000 reports of those adverse events. That’s a drop in the bucket if you consider more than 360,000 jabs were given out in that time period.

It’s also worth pointing out that whether someone ends up filing a report depends on a whole lot of other factors besides the vaccine itself: whether they’d been thinking about the side effects, if they’d been wary of it in the first place or how many other people were getting the vaccine at the time.

What are the most commonly reported adverse events in New Zealand?

For the Covid-19 vaccine they’re headache, dizziness, pain at the injection site, nausea and tiredness. Some people may have more than one, others may have none at all.

The vast majority of adverse events (more than 96%) weren’t serious. Of the serious ones, the most common is anaphylaxis or severe allergic reaction, which can be treated. That’s why they ask you to stay for 20 minutes after getting any vaccine.

Why do we get side effects from vaccines?

There are two main reasons according to Dr Frances Priddy, the Clinical Evaluation Director for Vaccine Alliance Aotearoa New Zealand.

First, some of the symptoms like muscle soreness or redness around the area are just from being jabbed in the muscle. “Even if you just injected some saline water you still would get a sore spot in your arm. Some of the soreness at the site of the shot, can just be from having a shot, regardless of what it is,” she told The Spinoff.

Second, it’s your body getting geared up to fight the virus in the future. From the body’s point of view, the vaccine is seen as a foreign invader. It can’t hurt you but the body goes to check it out and mop it up. That’s called the innate immune response.

The long-lasting immunity bit comes from what’s called adaptive immunity, where the body makes disease-fighting cells, T-cells or B-cells for example, and antibodies, which protect against infection when exposed to the virus later on. That process can also churn up some side effects.

Side effects are one of the signs that the body is learning to fight the virus, which is a good thing!

So, if I don’t have side effects does that mean the vaccine isn’t working?

No. You can’t always tell what your body is up to, explains Dr Priddy. “Your body has immune responses all the time and you’re not having side effects all the time,” she says. “If you don’t feel anything, don’t worry, it’s still working.”

What about blood clots?

These are extremely rare worldwide. More on that here.

New research done by New Zealand and Scottish scientists shows that there’s no link between the Pfizer–BioNTech vaccine (the one given here) and blood clots and other bleeding events. They found that out by looking at more than 2.5 million Scottish adults who got their first jab.

They did find some link however between the Oxford–AstraZeneca and those side effects. This vaccine isn’t currently approved for use in New Zealand.

Why do different people experience different side effects?

Short answer: We don’t really know.

There’s no real trend across the board for different vaccines and different people, says Dr Priddy.

Based on clinical trials of the vaccine, those under 65 often report having side effects. Based on data collected during the first vaccine rollout in the US, women also reported side effects more often. Whether this comes down to self-reporting or something biological is unclear.

But, I’m worried.

That’s natural and OK, says Dr Priddy. “It’s an unusual situation we’re in. Everyone’s got their antennae up because it’s a pandemic, this is a disease that could kill you, there are all these new vaccines … everyone’s on high alert.”

What is critical to remember, she says, is that vaccines have done way, way more good than harm.

“We’ve been using vaccines for a long, long time. If you look at good scientific studies, there are no clear long-term side effects of vaccines.”

What should I do if I’m worried about how I’m feeling?

The Ministry of Health says that if you’re unsure about your symptoms or if they get worse, call Healthline on 0800 358 5453.

If you’re concerned about your safety, call 111. Tell them you’ve had a Covid-19 vaccination so they can assess you properly.