COVID-19 Vaccines: What You Should Know

Last updated on 11 November 2022

As of 8 November 2022, 80% of the eligible population in Singapore have achieved minimum protection, and 69% of the same group are up-to-date with their vaccinations.

The vaccines all protect against severe and symptomatic forms of COVID-19, and they are helping to blunt the spread of the SARS-CoV-2 virus, the cause of COVID-19. Bivalent COVID-19 mRNA vaccines targeting both the original SARS-CoV-2 virus and more recent variants such as Omicron are also now available.

Technology and the Different COVID-19 Vaccine Types

There are over 10 COVID-19 vaccines in use in various parts of the world, using different types of vaccine technologies. There are 4 main vaccine types available. These include 2 genetic vaccines using either mRNA or DNA to deliver the instructions for making the COVID-19 antigen; in this case, that's the SARS-CoV-2 spike protein which in turn elicits an immune response and provides protection against the coronavirus. Other more conventional vaccines involve using either whole inactivated viruses or fragments of the virus to provoke immune protection.

mRNA Vaccines

Both the Moderna and Pfizer-BioNTech/Comirnaty* vaccines use mRNA (messenger RNA) technology. The current COVID-19 mRNA vaccines are the first to be approved for human use, however technology and research behind this vaccine platform has been over 30 years in the making. mRNA vaccines work by injecting pieces of the virus’ genetic code into the body to provoke an immune system reaction which then enables the body to defend itself against the coronavirus. The mRNA in the body breaks down fully within 48 hours. As it doesn’t enter the human nucleus, it does not affect human DNA. Both mRNA vaccines require 2 doses for adequate protection, and the doses are administered at least 3 – 4 weeks apart.

*Comirnaty vaccines carry the same research name as the Pfizer-BioNTech COVID-19 vaccines, BNT162b2. HealthHub records will be updated accordingly and the vaccine will now be labelled Pfizer-BioNTech / Comirnaty.

Modified Viral Vector Vaccines

Oxford AstraZeneca, Johnson & Johnson, CanSino and Sputnik V vaccines employ a modified harmless “delivery” or shuttle virus to introduce instructions to the person’s cells to make viral proteins; the body’s immune system then mounts a defence against it. The delivery virus is attenuated or modified so that it cannot cause you to fall sick, though you may experience short term symptoms that feel like the common cold.

Inactivated Whole Virus Vaccines

Sinovac and Sinopharm are inactivated whole virus vaccines, in which the virus is weakened or deactivated. This type of vaccine is effective in triggering an immune response but may require booster shots to maintain sufficient protection. Inactivated whole virus vaccines are well-established, and they are suitable for use even in those who have compromised immune systems.

Protein Subunit Vaccines

Protein subunit vaccines such as Novavax use only specific parts of the virus which are sufficient to trigger an immune response. This type of vaccine helps to minimise the risk of side effects, is suitable for those with compromised immune systems but may require booster shots. Novavax is presently undergoing phase 3 clinical trials, and may be available in Singapore by end-2021.

What are the differences in efficacy?

All currently approved vaccines protect well against severe COVID-19 disease, death and the need for hospitalisation. The various vaccines differ in their protection against clinical infection, duration of immunity and protection against new viral variants.

Here is a look at the vaccines on the WHO Emergency Use Listing and their efficacy:

Pfizer-BioNTech/Comirnaty’s vaccine has a reported 95% effectiveness while Moderna/Spikevax’s has charted a 94% efficacy. Conversely, Oxford AstraZeneca’s vaccine measured 70% efficacy overall, although there was a small group of volunteers that received a lower dose and recorded a higher 90% efficacy. Also, Sinovac-CoronaVac has been found to be 50.4% effective – barely over the 50% needed for regulatory approval.

Additionally, the vaccines require storage at very low temperatures. The Pfizer-BioNTech/Comirnaty vaccine needs to be stored at around –70 Celsius while the Moderna/Spikevax vaccine can be stored at –20 Celsius. This means that transportation and distribution will pose challenges.

Vaccines available under Singapore’s National Vaccination Programme

Under Singapore’s National Vaccine Programme, COVID-19 vaccination is free for all Singaporeans and long-term residents in Singapore.

There are currently 4 vaccines available under the programme:

• Pfizer-BioNTech/Comirnaty
• Moderna/Spikevax
• Novavax/Nuvaxovid
• Sinovac-CoronaVac

You are considered to have achieved minimum protection if you have gotten 3 doses of Pfizer-BioNTech/Comirnaty, Moderna/Spikevax, or Novavax/Nuvaxovid, or 4 doses of Sinovac-CoronaVac. The updated bivalent vaccines are recommended for keeping up-to-date with your COVID-19 vaccination. They can be taken once 5 months have passed since your last vaccine dose.

Let’s take a look at these 4 vaccines more closely.

Moderna/Spikevax and Pfizer-BioNTech/Comirnaty vaccines

In Singapore, the Expert Committee on COVID-19 Vaccination have confirmed both Moderna/Spikevax and Pfizer-BioNTech/Comirnaty vaccines have a consistent vaccine efficacy of around 90%. This is based on pivotal Phase 3 clinical trials as well as roll-outs around the world, with assessments from international regulatory bodies such as the US Food and Drug Administration (US FDA) and British Medicines and Healthcare Products Regulatory Agency (MHRA) confirming that mRNA vaccines continue to be effective against COVID-19.

Moderna/Spikevax and Pfizer-BioNTech/Comirnaty have also developed bivalent vaccines that have been approved for administration in Singapore. Bivalent vaccines target both the original COVID-19 virus strain, and the Omicron variants.

Both the Pfizer-BioNTech/Comirnaty vaccine and the Pfizer-BioNTech/Comirnaty bivalent COVID-19 booster vaccine are available to those aged 12 and above. The Moderna/Spikevax COVID-19 vaccine is available to those aged 6 months to 4 years old, and those 18 years old and up, while the bivalent Moderna/Spikevax vaccine is only available to those aged 18 and above.

For more information on bivalent vaccines, you may read our article Bivalent COVID-19 mRNA vaccines: All You Need to Know.

Novavax/Nuvaxovid vaccine

As of 13 May 2022, those aged 18 years and above have been able to receive the Novavax/Nuvaxovid vaccine for their primary vaccination series or as a booster. This vaccine is the recommended vaccine for those who are medically ineligible to receive the mRNA vaccines.

The Expert Committee on COVID-19 Vaccination has asserted that mRNA vaccines are preferred, however, due to their higher efficacy and ability to generate a stronger immune response.

Sinovac-CoronaVac vaccine

The Multi-Ministry Taskforce has included the Sinovac-CoronaVac COVID-19 vaccine in the National Vaccination Programme. The Expert Committee on COVID-19 Vaccination has asserted that the Sinovac-CoronaVac vaccine is less effective than mRNA vaccines, and is therefore best reserved for those who are medically ineligible to take any mRNA vaccine, or who have had allergies or severe adverse reactions to their first or second dose of a mRNA vaccine.

It won’t be offered as a booster to those who have no allergies or severe adverse reactions to mRNA vaccines. You must be 18 years or older to get this vaccine.

Myths & misconceptions

As with any medical innovation, there are a few misconceptions about the COVID-19 vaccines that have made its way through social media and messaging platforms.

Many people are under the impression that the production of these COVID-19 vaccines was rushed to be put on the market, and have not completed enough clinical trials.

In the past, traditional vaccines take an average of about 10 years to develop and don’t usually get approved in less than 5 years. A multitude of fortuitous events allowed for the rapid development of an effective COVID-19 vaccine. This included the massive amounts of public funding that were committed to support the development and manufacturing of the vaccines. The technology used in the mRNA vaccine had also been in development already for a few decades; it was novel and amenable to rapid design and deployment. Further, given the urgency of the pandemic and degree of volunteerism, large vaccine clinical trials could be undertaken; this was done without any compromise in quality or standards. The global scientific community also displayed tremendous unity to combat the new virus with an extraordinary amount of data sharing and transparency.

Advances in technology have also streamlined data-recording while social media made it easier to recruit people for human trials. As for approval, a ‘rolling review’ process – where information is released to healthcare regulators as soon as new data was acquired – helped speed up a process that would have traditionally taken between 6 – 9 months to achieve when data was submitted in batches.

Another commonly held misconception is the effect of mRNA on the body. There is fear the mRNA vaccine may permanently and irreversibly alter our body’s genetic structure. That couldn’t be further from the truth. This is because mRNA, (messenger RNA) in the vaccines does not enter the nucleus of human cells where our DNA lies. Further, mRNA degrades quickly and does not persist or integrate into the human genome.

How long have the COVID-19 vaccines been in use in Singapore?

Singapore received its first shipment of the Pfizer-BioNTech (now Pfizer-BioNTech/Comirnaty) COVID-19 vaccine on 21 December 2020 and the Moderna (now Moderna/Spikevax) vaccine was endorsed by the Expert Committee on COVID-19 Vaccination in February 2021.

The bivalent Moderna/Spikevax vaccine was made available on October 14 2022, with the Pfizer-BioNTech/Comirnaty bivalent COVID-19 booster vaccine available in late 2022.

The first shipment of the Novavax/Nuvaxovid vaccine arrived in Singapore on May 4 2022, and the Sinovac-CoronaVac vaccine was granted an interim authorisation by the Health Sciences Authority (HSA) under the Pandemic Special Access Route (PSAR) on October 23 2021.

As of 22 July 2021, IHH Healthcare Singapore has obtained approval from the Health Sciences Authority of Singapore to import the COVID-19 Sinopharm vaccine under the Special Access Route (SAR) scheme. Do discuss your suitability for the COVID-19 Sinopharm vaccine with your doctor if you intend to take the vaccine. You may book an appointment to receive the COVID-19 Sinopharm vaccine here.

Note that even after receiving the vaccine, we still have to do our part by continuing to keep our hands clean with regular hand washing and sanitisation, and abiding by mask-wearing rules.

Who can take the COVID-19 vaccines?

Individuals aged 18 and above can receive the vaccines offered in the National Vaccination Programme. This includes the bivalent mRNA vaccines as well as the Sinopharm vaccine offered under the Special Access Route (SAR) scheme.

Children aged 6 months to 4 years will be able to take the Moderna/Spikevax COVID-19 vaccine, and those aged 12 and up will be able to take both the Pfizer-BioNTech/Comirnaty vaccine and Pfizer-BioNTech/Comirnaty bivalent booster vaccine.

Pregnant or breastfeeding women are able to take the mRNA-based Pfizer-BioNTech/Comirnaty vaccine, Pfizer-BioNTech/Comirnaty bivalent booster vaccine, Moderna/Spikevax COVID-19 vaccine, and bivalent Moderna/Spikevax vaccine. As mRNA-based vaccines are not live vaccines, they are unlikely to affect breastfed babies and there have been no vaccine-related side effects reported in babies who were breastfed by mothers who were vaccinated while breastfeeding.

Who should not receive the COVID-19 vaccines?

• Those with a history of allergic reactions of anaphylaxis to the mRNA COVID-19 vaccines or its components. Anaphylaxis is a severe, life-threatening reaction which includes two or more of these three criteria: hives or swelling of the face, eyelid, lip or throat; difficulty breathing; or dizziness. If you have experienced these symptoms with other vaccines, you may be able to receive the COVID-19 mRNA-based vaccines if you have been evaluated by a specialist and deemed suitable. A referral to a specialist may be provided at vaccination sites, and the evaluation will be fully subsidised. Those with a history of anaphylaxis to other medications, food, insect stings or unknown triggers may still be vaccinated.


• Individuals who are severely immunocompromised, which includes those who have received an organ or stem cell transplant within the past 3 months, undergoing aggressive immunotherapy for non-cancer conditions, receiving HIV infection with CD4 < 200 cells/mm³

If you have yet to achieve minimum protection against COVID-19 or are due for a booster shot, please do so to protect yourself against COVID-19.

Article reviewed by Dr Adrian Ong, infectious disease specialist at Mount Elizabeth Hospital.

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