6.OCT.2021 7 MIN READ | 7 MIN READ

With bivalent COVID-19 mRNA vaccines added to the vaccine booster programme in Singapore, we revisit how they can help bolster our protection against COVID-19.

Last updated on 11 November 2022

What is a booster shot?

Booster shots are not a new phenomenon. They are commonly used for viral infections such as the flu, as well as other diseases such as Hepatitis A. Most vaccine boosters are identical to the previous doses, but some are modified to enhance their efficacy. For example, the new bivalent COVID-19 mRNA vaccines.

Why do we need COVID-19 booster shots?

Why do I need a COVID-19 booster shot?
Some may be wondering if the introduction of booster shots means that the current COVID-19 vaccines are not effective enough. This is not the case. While the COVID-19 vaccines effectively protect against COVID-19 and its variants, the level of protection can decrease over time. Receiving a booster shot can increase an individual’s level of immunity and protection from COVID-19 and its variants.

Israeli health officials have said that the effectiveness of the second dose of the Pfizer-BioNTech/Comirnaty vaccine decreased 6 months after it was given, necessitating the administration of a booster dose to provide increased protection. Similarly, there is evidence that antibody levels after 2 doses of Sinovac’s CoronaVac COVID-19 vaccine are low, and decline rapidly in all age groups within 3 to 6 months, returning to pre-vaccination levels by 6 months.  A third dose of CoronaVac is necessary to increase in antibodies and strengthen the immune protection against COVID-19. 

Besides the general population, individuals who are severely immunocompromised, such as cancer patients, transplant patients and patients on immunosuppressive therapy are particularly in need of a COVID-19 booster shot. This is because such individuals do not have as strong an immune response to the vaccinations as the typical population does. A booster shot would help to increase their immune response to an adequate level.

What COVID-19 booster shots are available?

COVID-19 booster vaccines are available in Singapore, and receiving an mRNA vaccine is encouraged, unless you are medically ineligible to. Non-mRNA booster vaccines such as Novavax/Nuvaxovid, Sinovac-CoronaVac, or Sinopharm vaccines are some alternative options.

The mRNA vaccines available in Singapore include the Moderna/Spikevax COVID-19 vaccine, the Pfizer-BioNTech/Comirnaty COVID-19 vaccine, and their bivalent options.

Are COVID-19 booster shots effective against COVID-19 and its variants?

Are the booster shots effective?
COVID-19 booster shots are effective against COVID-19 and its variants. A booster dose will ensure that your immune system is able to mount a stronger and longer lasting immune response against severe COVID-19 disease.

The bivalent COVID-19 mRNA booster vaccines approved for use in Singapore offer protection against 2 different variants of the COVID-19 virus – the original SARS-CoV-2 virus, and the Omicron variant(s). They also offer better protection against newer variants like XBB.

Are COVID-19 booster shots safe?

Data recently published by Pfizer and BioNTech suggests that the side-effects of their third vaccine dose were typically mild to moderate, with the frequency of such side-effects being similar to or better than the second dose. The most common side-effects experienced by recipients included injection site pain, fatigue, headache, muscle and joint pain, and chills. Individuals who have experienced an allergic reaction or anaphylaxis to the vaccines, or myocarditis or pericarditis after getting the vaccines, should not be vaccinated with a COVID-19 booster shot.

When should I take my COVID-19 booster shot?

In Singapore, those who took two mRNA vaccines as their primary vaccine series are recommended to receive a booster dose of an mRNA vaccine at least 5 months after the second dose of mRNA vaccine. On the other hand, immunocompromised individuals are recommended to receive their third dose of the same mRNA vaccine 2 months after their second dose. For those who took two doses of Sinovac-CoronaVac or Sinopharm, the third dose should be taken 90 days after the second dose.

Can I use a different vaccine for my booster shot?

Which COVID-19 booster shot should I choose?

In Singapore, persons who received two doses of mRNA vaccines can receive either Pfizer-BioNTech/Comirnaty or Moderna/Spikevax bivalent mRNA vaccines as booster shots. As such, the booster mRNA shot does not need to be same brand as the first two mRNA vaccines. Persons who have received two doses of Sinovac-CoronaVac or Sinopharm but are able to receive the mRNA vaccines are recommended to receive a PSAR mRNA vaccine as the third dose of the primary vaccination series.

MOH does not recommend the use of Sinovac-CoronaVac or Sinopharm as a booster vaccination. The exception is for persons who are unable to receive an mRNA vaccine due to medical reasons, such as an allergy to the mRNA vaccine.

Will booster shots have to be taken each time a new COVID-19 variant emerges?

There are now bivalent mRNA vaccines from Moderna/Spikevax and Pfizer-BioNTech/Comirnaty that are developed to offer better protection against the original SARS-CoV-2 virus, and the Omicron variant(s). As more variants emerge, vaccines may also evolve to protect against them.


Article reviewed by Dr Edwin Chng, medical director at Parkway Shenton, The Arcade (level 19)


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