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Long-term effects of vaccines

A multi-generational family walks on the beach

A common concern about the COVID-19 vaccines is that since they have only been around a short time, we don’t yet know if there will be any long-term effects.

While the vaccines themselves are new, we have huge amounts of research on vaccines and how they affect us. The ingredients in COVID-19 vaccines have been extensively researched and tested and how they work in your body. Australia has very robust safety monitoring for all vaccines and medicines from the Therapeutic Goods Administration (TGA) which is an independent authority.

It is very rare that a vaccine has needed to be removed after approval by the TGA, and in cases where this has happened, the adverse events were known about soon after the vaccine was being used. We have never seen side effects appear more than a few weeks after a vaccine, despite extensive research looking for long-term effects.

Vaccines don’t last long in your body

Much like food and medicines, vaccines don’t last long in the body. Once they’ve entered your body, you immediately begin processing them—which stimulates an immune response and leaves a lasting 'memory' for later—then your body disposes of them as waste.

The active ingredients in vaccines, mRNA used in Pfizer and Moderna vaccines or modified Adenovirus used in AstraZeneca, is completely disposed of by your body within a few days. The other ingredients like lipids, emulsifiers and preservatives that help deliver the vaccine safely to your cells are processed within a day or so.

Read more about COVID-19 vaccine ingredients

Immune systems are built for speed

Following a vaccination, your immune system will be activated and start building its memory of how to fight off this intruder. Your immune system acts quickly: that’s how it manages to fight off infections.

Most side effects appear in the first few days after the vaccination and are usually mild. These are signs that the immune system is active and responding to the vaccine as intended. Based on past experience with vaccines, problems will appear quickly, generally within the 6 weeks following vaccination. These side effects are generally mild and low risk.

After those first few weeks, you keep the immune memory – but your immune system is no longer being activated. This is why we generally don’t see any reactions after this time.

So after vaccination, there’s a known period of risk (up to about 6 weeks) in return for long-term benefit of immunity which usually lasts 12 months or longer … it’s a pretty good deal.

Immunity from vaccination is safer than exposure

As opposed to the more commonly known side effects of vaccination, occasionally rare adverse events can happen in response to the immune system activation that occurs from a vaccine. However, the immunity we achieve from vaccination is much less risky than immunity we would get through exposure to a pathogen like the virus that causes COVID.

We do not have long-term research on the health impacts of COVID-19, however we do know the virus can damage the lungs, heart and brain, which increases the risk of long-term health problems.

We now do know there is a very rare and serious risk of clotting disorder thrombosis with thrombocytopenia syndrome (TTS) from the AstraZeneca COVID-19 vaccine or potentially heart conditions myocarditis or pericarditis from Pfizer and Moderna vaccines, and most importantly, we know how to identify and treat these conditions.

These events will usually occur within weeks to at most a few months after vaccination, not years. It took us a little longer to find out about these particular side effects because they’re so rare, and we need to be careful not to confuse “long-term” effects of a vaccine with “so rare it takes a long time to find.”

This is true of all medicines as they move from clinical trial populations in the thousands to real-world application in the millions. The urgency of getting the global population vaccinated against COVID-19 means we have been able to very quickly identify these rare side effects, within a matter of months. The frequency of these side effects is still very low, approximately 1 in every 200,000, we are just seeing them in a concentrated timeline.

If you still have questions, speak with your doctor

It’s perfectly reasonable to be wary of new treatments, especially if you don’t feel like you’ve got all the information you need, or you’ve seen information that has you worried. Your GP can help break down the science, and discuss risks and benefits based on your personal medical history, including the risks of choosing not to take the vaccine.

More information on the COVID-19 vaccines (including Moderna):

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Last updated: 20 October 2021