How the Moderna vaccine works against Covid-19

Australia has just welcomed its new vaccine from Moderna. Experts reveal how it works, its side effects and who can get it.

Australia has just welcomed its new vaccine from Moderna. Experts reveal how it works, its side effects and who can get it.

How does the Moderna Covid-19 vaccine differ to the other two currently available in Australia (Pfizer and AstraZeneca)?

The Moderna (Spikevax) Covid-19 vaccine is a Messenger RNA (mRNA) vaccine. The Pfizer (BioNTech) vaccine is also a mRNA vaccine, while AstraZeneca (Vaxzevria) is known as a vital vector vaccine. Both vaccine types deliver genetic code instructions to make a Covid-19 spike protein, which leads to an immune response that is designed to prevent you becoming ill from Covid-19.

How does it work?

The Moderna vaccine uses a synthetic genetic code called RNA to give your body’s cells instructions on how to make the coronavirus’ unique spike protein. After getting the vaccine, your body makes copies of the spike protein. When your body has made the protein encoded by the mRNA vaccine, it then recognises the spike protein as being foreign and launches an immune response against it. Your immune system will then learn to recognise and fight the SARS-CoV-2 virus that causes Covid-19. Protection against Covid-19 takes effect about two weeks after the first dose of Moderna. One dose gives some protection, while two doses will give optimal protection. No vaccine is 100 per cent effective, so it is possible that you can still get infected and sick from Covid-19 after vaccination. This means it is still important to continue other preventative measures like social distancing, hand washing and sanitising, wearing a face mask, undergoing testing when symptoms occur and observing quarantine/isolation directions.

How long does it stay in the body?

The genetic code is broken down quickly by the body. The RNA from the vaccine does not change or interact with your DNA in any way. The Moderna vaccine does not contain any live virus, and it cannot give you Covid-19. The vaccine is administered in two doses, given four-six weeks apart. In some circumstances this interval may be longer, but will be decided in consultation with your immunisation provider and/or health professional or GP if necessary.

What are the common side effects?

Side effects reported in a clinical trial following administration of the Moderna vaccine include pain at the injection site, mild fever, fatigue, headache, joint pain, muscle pain, chills, nausea/vomiting, swelling/tenderness in the armpit, fever, swelling and/or rash at the injection site. These are typical responses that show the immune system is responding to the vaccine. Recent research suggests that some increase in body temperature (such as mild fever) may actually help the body’s response to vaccination. The National Prescribing Service (NPS) has an Adverse Medicine Events (AME) Line that you can call to report side effects. It operates from 8am-8pm Monday to Sunday and is contactable on 1300 134 237.

What are the rare side effects?

A severe allergic reaction to the vaccine is rare and would usually occur within a few minutes to one hour after receiving a dose of the Moderna vaccine. This is why a vaccination provider may ask you to wait for a period of time for monitoring after the vaccine is administered. Myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the lining outside the heart) have occurred in some people who have received the Moderna vaccine. In most cases, symptoms began within a few days after the second dose. Both conditions require diagnosis by a doctor, and are based on medical history, a physical examination and diagnostic tests.

Is there anyone who should NOT have the vaccine?

You should not have the Moderna vaccine if you have a known known history of severe allergic reaction, such as anaphylaxis, to a previous dose of a mRNA Covid-19 vaccine, or to any component of the Moderna vaccine, including polyethylene glycol (PEG). You should also not have the vaccine if you have had myocarditis and/or pericarditis attributed to a previous dose of a mRNA vaccine; or any other serious adverse event, that following review by an experienced immunisation provider or medical specialist was attributed to a previous dose of a mRNA vaccine that had no other identifiable cause. Anyone with chronic health conditions, including heart conditions or weakened immune systems (immunocompromised patients) should seek advice from their GP or specialist before having the Moderna vaccine. The Australian Government strongly recommends immunocompromised people receive vaccination against Covid. Moderna is not a live vaccine and is safe for use in people who are immunocompromised.

What is the efficacy rate after vaccination?

A major new study of vaccine effectiveness against Delta in 32,000 people by the US CDC came out over the weekend.

It shows Moderna is even more effective than Pfizer against the Delta variant.Moderna’s vaccine is 95 per cent effective at preventing hospitalizations with Delta, while Pfizer sits at 80 per cent. Moderna is 92 per cent effective at preventing the need for urgent care and emergency room visits from Delta while Pfizer is 77 per cent effective on this measure.

There could be two reasons for this. Moderna contains three times more mRNA than the Pfizer jab and the interval between jabs is four weeks for Moderna instead of three weeks for Pfizer.Research suggests longer gaps between shots improves immunity.

Is Moderna safe for pregnant and/or breastfeeding women?

According to the Australian Health Department, pregnant women should be routinely offered one of the mRNA-based Covid vaccines, Pfizer or Moderna, at any stage of pregnancy. Pregnant women who contract Covid-19 have an increased risk of severe illness and adverse pregnancy outcomes. Real-world evidence has shown that Moderna is safe for pregnant women and breastfeeding women. You do not need to stop breastfeeding after Moderna vaccination.

Originally published as How the Moderna vaccine works against Covid-19