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COVID-19 is an ongoing pandemic and the information will be updated as we know more

(last update 20 Apr 2023)

Vaccine hesitancy and nationalism are barriers to a national vaccination program. COVID-19 is no different. This page will summarise the efficacy and safety data of the various vaccines that are available locally. This is not meant to be a comprehensive  review and will be limited to vaccines which are available in Singapore and this region. 

This article from Nature summarises the 8 major ways a vaccine can be made.


mRNA Vaccines (Pfizer/BioNTech BNT162b2 and Moderna mRNA-1273)

Pfizer / BioNTech BNT162b2 Phase 1 and 2 - BNT162b2 is more efficacious than BNT162b1 in generating neutralizing GMT antibodies. 

Pfizer / BioNTech BNT162b2 Phase 3 - safety and efficacy in a large (n = 43,548) study with half given placebo. Efficacy was defined as symptomatic infection AND positive COVID-19 PCR test. This shows 95% efficacy for confirmed COVID-19 cases (8 vs 162 cases). None of the subjects who had the vaccine had moderate or severe COVID-19. (Published 10 Dec 2020). Note that there was a single case of severe COVID-19 in the vaccine group but that was seen in a patient who only had 1 dose and 9 cases of severe COVID-19 in the placebo group.

Moderna mRNA-1273 Phase 3 - safety and efficacy in a large (n = 30,420) study. Efficacy was defined as symptomatic infection AND positive COVID-19 PCR test. This shows 94% efficacy for confirmed COVID-19 cases (11 vs 185 cases). Severe COVID was seen in 30 patients on placebo and none of the subjects who had the vaccine had moderate or severe COVID-19. (Published 30 Dec 2020)

Risk of Myocarditis with mRNA vaccines (10 June 2021)

US FDA and CDC published their data from the Vaccine Adverse Event Reporting System (VAERS) on the 10 June 2021 (11 June 2021 SGT) on the increased risk of myocarditis in young (< 24 yrs old) and male subjects who had received both mRNA doses. (link to presentation).

Position Statement from Singapore Cardiac Society and Academy of Medicine (14 June 2021)

Various reports suggest that COVID19 infection is associated with both myocarditis and pericarditis. Published rates vary widely. In the largest and most complete of these studies, all patients (all young competitive athletes) who had prior COVID19 infection underwent cardiac MRI scans. The study showed that the incidence of myocarditis was 2.3% (ranging from 0 to 7.6% at different institutions) i.e. the equivalent of 2,300 per 100,000 patients infected with COVID19.

Preliminary estimates from the USA suggest that the overall risk from the second dose of the mRNA vaccines is about 1.6 cases per 100,000 doses, with risk primarily in males under the age of 30. The risk of myocarditis in those age 12 - 24 yrs old is ~ 2.3 per 100, 000. 


The risk of complications from COVID19 infection continues to far outweigh the
risk from COVID19 vaccines (2300 vs 2.3 per 100,000) 

Israeli Real World Data 

Israel was the first country to get a large percentage of their population vaccinated with the Pfizer/BionTech mRNA vaccine and they have good data to show safety and efficacy. 

They confirm that there is increased risk of Myocarditis with vaccines, but they also showed that risk of Myocarditis in unvaccinated folks are many times higher. 



Inactivated Vaccines (CoronaVac by Sinovac 北京科兴生物制品

Sinovac Coronavac Phase 1 and 2 - Neutralising antibodies was seen for 109 (92%) of 118 participants in the 3 μg group. 

Sinovac Coronavac Phase 3 

Studies were conducted in Brazil, Turkey, Indonesia, and Chile by respective national institutes. Efficacy rates differ as they were conducted in groups with different risk profile and risk of infection. Brazil has the largest cohort and enough positive cases to perform statistical analysis with 12, 396 subjects recruited. 

Brazilian Data 

PROFISCOV Study (NCT04456595)

(Clinical Trial of Efficacy and Safety of Sinovac's Adsorbed COVID-19 (Inactivated) Vaccine in Healthcare Professionals)


Press Release (December 16, 2020) (link to Butantan Insitute press release in Portugese)

Phase 3 data published by Butantan Institute as a press release

n = 12,396 mainly health care workers over 18 years old (limited number of > 60 year olds were recruited)

253 positive cases were collected during the observation period (2% infected) which allowed statistical analysis.

Efficacy measured 14 days after following vaccination with both doses of vaccine using symptoms AND positive PCR test.

Grade 2 - mild infection which does not require medical attention

Grade 3 - mild infection which requires some form of medical attention 

Grade 4 (and above) - moderate to severe cases that needs hospitalisation 

Efficacy rate against diseases caused by COVID-19 was

1. 50.39% for Grade 2 and above (167 vs 85 cases in placebo vs vaccine) 

2. 83.7% for Grade 3 and above 

3. 100% for Grade 4 and above i.e. hospitalized, severe, and fatal cases (7 vs 0 cases in placebo vs vaccine) 

None of the subjects who had the Sinovac vaccine had moderate or severe COVID-19. There were no serious adverse reactions to the vaccine in their cohort. 

Pre-approval PROFISCOV Study (14 April 2021)


Chinese Center for Disease Control and Prevention (China CDC) release safety data from National Vaccination Programme (31 May 2021)

Based on data after 265 million doses of (presumably mainly inactivated) vaccines that was given; an adverse event rate of 11.86 out of 100,000 and a serious adverse event rate of 0.07 in 100,000 was presented. The nature of these adverse events was not available from this publication.

Safety Monitoring of COVID-19 Vaccines in Hong Kong (30 May 2021)

Adverse events reported based on 1.0 million doses of CoronaVac (Sinovac) and 1.4 million doses of Comirnaty (Fosun-BioNTech). Cases of hospitalisation post vaccine was 126 for Coronavac and 273 for Fosun-BioNTech (Comirnaty). With 1,014, 800 doses of Coronavac and 1,349,200 doses of Comirnaty given, this translates to 0.012% and 0.020% risk of hospitalisation for Coronavac and Comirnaty respectively. The severity, nature and outcome of these hospitalisation are not known and the causal relationship of the vacccine and hospitalisation have not been established (and won't be in view of the nature of this kind of data). But these numbers are useful to estimate "worse case scenarios"

Safety Monitoring of COVID-19 Vaccines in Hong Kong



WHO approves Coronavac by Sinovac (1 June 2021)

Singapore MOH approves Coronavac by Sinovac under Special Access Route (4 June 2021) 

Post surveillance data from Chile (published 7 July 2021)


65.9% for the prevention of Covid-19

87.5% for the prevention of hospitalization

90.3% for the prevention of ICU admission

86.3% for the prevention of Covid-19–related death


data for > 60 yr olds reduced but broadly similar 


(click on pdf icon for full paper)

(right mouse click on table to open in new tab / window to enlarge)  



mRNA vs Inactivated Vaccine (WHO link

All the vaccines shortlisted have shown 100% efficacy in protection against the clinically important moderate to severe COVID-19 infection requiring hospitalisation in the study population.


The difference in efficacy between the mRNA and inactivated virus appears to be limited to the mild to very mild cases. Note that the way Pfizer / Moderna defines mild cases differs from the way Butantan Institute defines it and the Butantan study had higher rates of severe cases on placebo demonstrating that the latter was truly conducted in a high risk setting. 

This Youtube video from Vox explains why it is hard to compare different vaccines tested in different populations 

mRNA vaccines's big advantage is that they are incredibly fast to make (proving that they work still depends on slow, careful and laborious phase 1 - 3 clinical studies). BioNTech and Moderna only needed the genetic code published online by Prof Zhang Yong Zhen (张永振) on 12th Jan 2020 to start making the vaccine. Scientists had already previously identified the spike protein as a vaccine target based on research on the 2003 SARS virus. This is why the clinical trials using mRNA based vaccine were the first off the block. They have also shown to be highly effective in generating antibodies which are assumed to be linked to efficacy. 


The biggest disadvantage of the mRNA vaccines are that they require super cold storage (minus 20 or 70 Celsius) conditions and this may be a problem in poorer countries or countries with large rural populations and may limit their utility in some countries. The risk of serious allergic reactions also limits their use in some patients with a history of severe allergies and we think this is due to the lipid shell that protects the mRNA vaccine. In Singapore there were 4 cases of severe reactions (out of 155, 000 persons vaccinated). All were identified, treated quickly and recovered fully. There is also now early data from US CDC to show an increased risk of myocarditis in young males (< 24 yr old) with the mRNA vaccines (10 June 2021).

Inactivated vaccines are the traditional way to make vaccines and the successful Influenza and Polio vaccines are made this way. The virus is killed or inactivated using chemicals or heat. It requires special facilities to grow the virus safely and production time is relatively long. Most inactivated vaccines elicit a milder response and will likely require two or even three doses to be administered - this can be both an advantage as well as disadvantage. The response may be muted in the elderly and immunocompromised, but they are also less likely to elicit an overreaction. Storage requirements are relatively simple and vaccines can be stored in a normal household refrigerator and this will be advantageous in poorer countries or countries with large rural populations. At present efficacy data on the very young and very old is limited. 

(Updated April 2023)

Singapore and Hong Kong has since published observational data comparing efficacy between the main vaccines approved for use. They show similar efficacy after 3 doses (HK data) and after 4 doses (SG data)

Hong Kong Efficacy Data 

Sinovac vs Pfizer with 2 or 3 doses

Singapore Efficacy Data 

Sinovac vs Pfizer vs Mixed 2 vs 3 vs 4 doses 

Bivalent Vaccine Boosters (updated 20 Apr 2023)

Currently there are 2 bivalent boosters available in Singapore, both are based on the Omicron (B.1.1.529) variants which have evolved into BA,1 to BA.5 variants (amongst others). All bivalent boosters will include the spike protein from the original wild type COVID19 first identified and isolated in Wuhan, China.

Current prevaling variants are rapidly evolving and it is useful to view updates from WHO

1. Moderna bivalent (Spikevax) which is based on the original wild type and the BA.1 spike protein

2. Pfizer bivalent (Cominarty) which is based n the original wild type and BA.4-5 spike protein

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