Severe Covid-19 symptoms 5 times more likely in patients who got Sinovac rather than Pfizer jab: Study

Sinovac vaccine recipients are also more than twice as likely to be infected with Covid-19 than Pfizer recipients. PHOTO: ST FILE

SINGAPORE - Recipients of the Sinovac-CoronaVac vaccine are five times more likely to experience severe Covid-19 symptoms when they are infected than those who had the Pfizer-BioNTech/Comirnaty vaccine.

Sinovac recipients are also more than twice as likely to be infected with Covid-19 than Pfizer vaccine recipients and almost six times more likely than those who took the Moderna vaccine.

These are the findings of a Singapore study which were published on Tuesday (April 12).

The study by infectious diseases experts looked at the difference in vaccine efficacy between mRNA vaccines, such as the Pfizer-BioNTech/Comirnaty and Moderna ones, and those which use an inactivated form of the Covid-19 virus.

Examples of the latter include Sinovac-CoronaVac and Sinopharm.

Among the study's authors are National Centre for Infectious Diseases (NCID) executive director Leo Yee Sin, Associate Professor Benjamin Ong from the NUS Yong Loo Lin School of Medicine, Ministry of Health (MOH ) senior assistant director Wycliffe Wei, NCID associate consultant Calvin Chiew, MOH Communicable Diseases Division director Vernon Lee, National University Health System junior resident M. Premikha and NCID Infectious Disease Research and Training Office director David Lye.

The study covered a seven-week period, from Oct 1, 2021, to Nov 21, 2021, and involved close to three million adults aged 20 years old and above who had received their first two doses of the Covid-19 vaccines.

Compared against people who opted for the Pfizer vaccine, Sinovac recipients were 2.37 times more likely to be infected with Covid-19, while those who were vaccinated with Sinopharm were 1.62 times more likely to be infected, the study found.

Those who got the Moderna vaccine were found to be 0.42 times, or less than half, as likely to show severe Covid-19 symptoms than Pfizer recipients, while those who had Sinopharm shots were 1.58 times more likely to experience severe symptoms.

Associate Professor Lye, in a post on Twitter on Wednesday, said: "Singapore study showed five times the risk of severe Covid with Sinovac vs Pfizer. Thankfully only 2 per cent are vaccinated with Sinovac."

The authors concluded, however, that even with the lower level of protection offered by inactivated whole virus vaccines than the mRNA vaccines, both types of vaccine give sufficient protection against severe Covid-19 symptoms and that vaccination remains a key strategy against the pandemic.

MOH has said that as at Tuesday, over 96 per cent of the eligible population have completed their full regimen of vaccinations, while 72 per cent have received their booster shots.

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