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A new Singapore study comparing the effectiveness of Covid-19 vaccines against infection and severe disease was published on Apr. 12, 2022.

The study set out to compare the four available vaccines in Singapore, looking into other studies' findings that mRNA vaccines have higher efficacy than non-mRNA vaccines.

The four vaccines are the Pfizer-BioNTech/Comirnaty vaccine and the Moderna vaccine, which are mRNA vaccines, as well as the Sinovac-CoronaVac vaccine and the Sinopharm vaccine, which are non-mRNA vaccines that use an inactivated virus to trigger an immune response.

The Pfizer vaccine was used as a reference as it was most commonly used in Singapore.

Findings

Here are the results of the study on how well the vaccines protected against Covid-19 infection:

• Those who received Sinovac-CoronaVac: 2.37 times more likely to be infected than those who received Pfizer
• Those who received Sinopharm: 1.62 times more likely to be infected than those who received Pfizer
• Those who received Moderna: 0.84 times as likely to be infected than those who received Pfizer

And here are the results of the study on how well the vaccines protected against severe disease arising from Covid-19 infection:

• Those who received Sinovac-CoronaVac: 4.59 times more likely to have severe disease than those who received Pfizer
• Those who received Sinopharm: 1.62 times more likely to have severe disease than those who received Pfizer
• Those who received Moderna: 0.42 times as likely to have severe disease than those who received Pfizer

"Severe disease" was defined as requiring oxygen supplementation in a hospital, admission to an intensive care unit, or death.

Comparing vaccines in the same population

"We aim to compare the mRNA and inactivated whole virus vaccines in the same population as the findings will be useful for guiding policy recommendations to prevent infection and reduce strain on the healthcare system," said the study's authors in the introduction.

The study looked at the incidence of Covid-19 infection and severe disease from Oct. 1 to Nov. 21, 2021, and made use of official databases maintained by Singapore's Ministry of Health (MOH).

Which individuals were subjects of the study?

Those who were partially vaccinated, boosted with a third dose, or previously infected were excluded from the study.

It excluded those who got their second dose within 14 days of the study period, to allow for sufficient immune response, as well as those who received their second dose more than 120 days before, to control for waning of immunity.

The study was also restricted to individuals aged 20 and above, as those under 18 were not allowed to receive the Moderna and Sinovac-CoronaVac vaccines.

Conclusion: Inactivated virus vaccines offer lower protection

The study's authors concluded that those who received two doses of inactivated whole virus vaccines had lower protection against Covid-19.

Nevertheless, they said that "both mRNA vaccines and inactivated whole virus vaccines provide sufficient protection against Covid-19 severe disease", and affirmed the importance of vaccination as "a key strategy" in the Covid-19 pandemic.

You can access the study's manuscript here.

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Top images via Nafis Fuad Ayon on Wikipedia and via Unsplash

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