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Everything you need to know about the Moderna COVID-19 vaccine

As more vaccines are approved in the UK, this article aims to focus on supporting pharmacy professionals with key learning points around the Moderna vaccine

Unplanned learning

This article was correct at time of publishing (March 11). For further news and updates please visit C+D’s COVID-19 hub

The Moderna vaccine was authorised for temporary supply by the Medicines and Healthcare Products Regulatory Agency (MHRA) on January 8.(1) The UK has ordered 17 million doses, with these expected to arrive by Spring 2021 due to scaling up of the European supply chain.(2)

How does it compare to other COVID vaccines?

The Moderna vaccine is very similar in action to the Pfizer/BioNTech vaccine. As with all the other vaccine candidates, it is not a live vaccine. It is a messenger RNA (mRNA) vaccine. It contains 100 micrograms of RNA per 0.5mL dose (versus Pfizer’s 30 micrograms of RNA per 0.3mL dose) encapsulated in a lipid particle. This mRNA denatures easily, hence the critical storage requirements. It lasts just long enough, once injected, to instruct the cells to generate a small piece of harmless spike protein, which the immune system then builds an immune response to. This mechanism protects individuals against COVID-19 should they be exposed.(3)

Trial data shows a 94.1% efficacy against contracting COVID-19, with a 95% efficacy against hospital admission in 30,000 participants. The lower dose Pfizer produces the same response.(4)

The Moderna vaccine is authorised for use in those 18 years and over, while the similar Pfizer vaccine is authorised for ages 16 and over.(3)



The Moderna vaccine contains polyethylene glycol/macrogol (PEG) as an excipient. As per the Pfizer vaccine, this can trigger allergic reactions in those who are sensitive to this ingredient. A 15-minute post vaccination observation is required in those receiving the Moderna vaccination, which mirrors the Pfizer/BioNTech requirements. The same requirements apply to this mRNA vaccine that those with allergies to any of the vaccine ingredients and a history of severe allergies should not receive a dose of this vaccine, but those with food allergies may.(3)

In two cases in the USA, people with a previous history of cosmetic skin filler injections experienced a serious adverse event of facial swelling following their Moderna vaccination. They recovered fully following the incident.(5)


Although it is recognised that the vaccine may not work as effectively in individuals who are immunocompromised, the vaccine is still recommended in this patient group.(3)

Pregnancy and breastfeeding

The updated guidance from the Joint Committee on Vaccination and Immunisation (JCVI) remains in place for Moderna because it is a similar vaccine to Pfizer/BioNTech.(6) This guidance is to consider vaccination on case-by-case basis for those who are clinically vulnerable or at risk in the workplace. The Green Book has been updated to reflect that there is no risk in breastfeeding women with Moderna.(3)


Similar risks exist with the Moderna vaccine administration and bleeding. One of the pre-screening questions will ask about bleeding risks and current anticoagulant medication control to support the vaccinator with needle choice and additional pressure to administration site.(3)

Side effects

There are similar side effects to the Pfizer/BioNTech vaccine with very common reactions (>1 in 10 people) including:(7)

  • tenderness and swelling of the underarm glands on the same side as the injection site
  • headache
  • nausea
  • vomiting
  • muscle ache, joint aches and stiffness
  • pain or swelling at the injection site
  • feeling very tired
  • chills
  • fever

The incidence of these very common adverse events was most frequently noted in younger age groups, below 65 years, with a greater occurrence of events after the second dose. Paracetamol may be recommended to relieve post-vaccination symptoms pharmacologically. They normally subside after a couple of days.(8)

In the USA, there have been at least 12 reported cases where patients developed a large red rash at the injection site up to 11 days after their vaccination. These are easily treated but can be worrying for people.(9)

How is it reconstituted and stored?

The Moderna vaccine does not require dilution. It can be stored at -25ºC to -15º C for seven months. Once the vial has been defrosted, it can be stored at fridge temperature and protected from light for 30 days. The unopened vial lasts for 12 hours at room temperature.

Once the vial has been punctured, it must be used within six hours and stored at a temperature of 2–25ºC.(8)


Each vial contains 10 doses and the vial should not be shaken but swirled gently after thawing and between each dose withdrawal.(8) The Moderna vaccine has been approved for administration as two doses at a 28-day interval, however the Green Book recommends an operational 4-12-week minimum interval for all the current vaccines.(3) Each dose is 0.5mL and is to be administered intramuscularly, ideally into the deltoid muscle.(8)

Upcoming vaccines

Novavax (an engineered protein vaccine), made in the USA, is estimated to be the next vaccine in line to be authorised in the UK, with 60 million doses on order. It has been shown to be 95.6% effective against the original COVID-19 strain,(10) 86% effective against the UK variant and is still currently 60% effective against the South African variant.(11) It is stored at fridge temperature. It is a two-dose vaccine, which does not require reconstitution, with a 21-day recommended interval between doses.(11)

Janssen, based in Belgium, has applied to the MHRA for temporary supply authorisation of its Johnson & Johnson (J&J) COVID-19 vaccine, with 30 million doses purchased in the UK. Their clinical trial data showed this vaccine to be 66% effective against moderate to severe disease and 85% effective against severe disease, with its main benefit being a single dose regimen. As with all the other vaccines, J&J showed a 100% efficacy against hospitalisation and death. It also has easy storage requirements of fridge temperature. If this is approved, the vaccine should be available in the latter part of 2021. This is an adenovirus vector type vaccine – similar to Astrazeneca.(12)

Valneva, from France, is the only inactivated whole virus vaccine candidate. The manufacturer is well underway with its trials and should be fifth in line to apply for authorisation in the UK, with 100 million doses on order.(13)

At the time of publishing (March 11), the UK had already vaccinated around 21 million people with their first dose of either the Pfizer/BioNTech or Oxford/AstraZeneca vaccine. With more vaccine options being approved, the supply will enable more of the population to be vaccinated more quickly. This will help to deliver phase 2 of the Joint Committee on Vaccination and Immunisation rollout, which includes the rest of the population aged 18-40, with the rollout continuing to work backwards through each decade of age groups.(14)

The availability of Moderna supports this rollout process well and pharmacists can feel comfortable continuing to encourage individuals to accept any of the vaccine options that they are offered.

  1. Gov.UK (2021) MHRA website approval of Moderna
  2. Gov.UK (2020) UK government’s response to Moderna’s publication of efficacy data for its COVID-19 vaccine
  3. Public Health England (2021) Green Book Chapter 14a: COVID-19 - SARS-CoV-2
  4. European Medicines Agency (2021) EMA recommends COVID-19 vaccine Moderna for authorisation in the EU
  5. Centre for Disease Control and Prevention (2020) Local reactions, systemic reactions, adverse events, and serious adverse events: Moderna COVID-19 vaccine
  6. Royal College of Obstetricians and Gynaecologists (2020) Updated advice on COVID-19 vaccination in pregnancy and women who are breastfeeding
  7. Gov.UK (2021) Information for UK recipients on COVID-19 vaccine Moderna
  8. Blumenthal, K et al. (2021) Delayed large local reactions to mRNA-1273 vaccine against SARS-CoV-2New England Journal of Medicine, [online]
  9. BBC News (2021) Covid-19: Novavax vaccine shows 89% efficacy in UK trials
  10. Mahase E. (2021) Novavax vaccine efficacy is 86% against UK variant and 60% against South African BMJ 2021; 372:n296 doi:10.1136/bmj.n296
  11. BBC News (2021) Johnson & Johnson Covid vaccine: FDA approves single-shot jab
  12. Valneva (2021) Valneva announces UK government exercise of option for 40 million doses of its inactivated, adjuvanted COVID-19 vaccine
  13. Gov.UK (2021) JCVI issues interim advice on Phase 2 of COVID-19 vaccination programme rollout
  14. Gov.UK (2021) People who have received vaccinations, by report date (daily)

Gavin Dobson, Academic pharmacist

Excellent and informative - thanks very much. There is much interest about the Moderna vaccine on social media. The VAC4COVID study is monitoring all UK-approved COVID vaccines, including AstraZeneca, Pfizer and Moderna.

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