AstraZeneca vs. Sinovac : Efficacy Against Gamma Variant

A large Brazil study just compared the efficacy of the AstraZeneca and Sinovac vaccines against the Gamma variant of COVID-19!

Here is what you need to know!

 

SARS-CoV-2 Gamma Variant : What Is It?

The Gamma variant of the SARS-CoV-2 virus (P.1) is one of the four Variants of Concern (VOCs). It was first detected in Brazil in November 2020, but has since spread to more than 10 other countries.

As this BBC comparison shows – it is more similar to the Beta (UK) variant than the Delta (India) variant. It shares two of the mutations of concern with the Beta variant, but none with the Delta variant.

The Gamma variant is less transmissible than the Delta variant, but has greater resistance to vaccines.

Therefore, the results of this study is of great interest to scientists and doctors who are worried about the effectiveness of current vaccines, if the Gamma variant becomes more prevalent.

 

AstraZeneca vs. Sinovac : TLDR Summary

The Brazilian study looked at 60.5 million Brazilians who were vaccinated with either the AstraZeneca Vaxzevria vaccine, or the Sinovac CoronaVac vaccine.

Here is our quick TLDR summary of their key findings :

AstraZeneca Vaxzevria

• breakthrough infections were high for people who were partially-vaccinated
• partially-vaccinated individuals had significant protection against hospitalisation, ICU admission and death
• fully-vaccinated individuals had very good protection against hospitalisation, ICU admission and death
• there was a big drop in vaccine effectiveness in people 90 years or older

Sinovac CoronaVac

• breakthrough infections were high, whether people were partially- or fully-vaccinated
• partially-vaccinated individuals had poor protection against hospitalisation, ICU admission and death
• fully-vaccinated individuals had good protection against hospitalisation, ICU admission and death
• there was a huge drop in vaccine effectiveness in people 90 years or older

Despite what Internet rumours may claim, the AstraZeneca vaccine is definitely superior to the Sinovac vaccine.

But the good news is – both vaccines offer good protection against the Gamma variant of COVID-19, with one caveat – only after individuals are fully-vaccinated.

 

AstraZeneca vs. Sinovac : Study Results Summarised

The Brazilian study was a retrospective study involving 60.5 million Brazilians from 18 January until 30 June 2021.

It compared the effectiveness of the AstraZeneca Vaxzevria and Sinovac CoronaVac vaccines in preventing :

• COVID-19 infection,
• hospitalisation,
• ICU admission, and
• death.

The study also noted that the Gamma variant was the most frequent variant in Brazil at the time it was conducted.

Partial Vaccination

The Brazilian team defined partial vaccination as 14 days or longer after receiving the first dose of a vaccine, but before receiving the second dose.

They found that partial vaccination with the AstraZeneca Vaxzevria vaccine offered significant protection against hospitalisation, ICU admission and death – about 50% better than unvaccinated people.

Partial vaccination with the Sinovac CoronaVac vaccine offered far less protection than the AstraZeneca vaccine.

Partial Vaccination	AstraZeneca	Sinovac
Infection	34.0%	16.4%
Hospitalisation	52.2%	26.6%
ICU Admission	54.0%	28.1%
Death	49.3%	29.4%

Full Vaccination

The Brazilian team defined full vaccination as 14 days or longer after receiving the second dose of a vaccine.

They found that people fully-vaccinated with the AstraZeneca Vaxzevria vaccine had good protection against getting infected with COVID-19, and very good protection against hospitalisation, ICU admission and death.

Full vaccination with the Sinovac CoronaVac vaccine offered significant protection against getting infected with COVID-19, and good protection against hospitalisation, ICU admission and death.

This shows the importance of being fully-vaccinated with either vaccine.

Full Vaccination	AstraZeneca	Sinovac
Infection	70.0%	54.2%
Hospitalisation	86.8%	72.6%
ICU Admission	88.1%	74.2%
Death	90.2%	74.0%

People 90 Years Or Older

The Brazilian team also identified a big drop in vaccine effectiveness in people who are 90 years or older.

This is a bigger problem for the Sinovac CoronaVac, which offers only 35% protection against death for this age group; and less so for the AstraZeneca Vaxzevria, which offers twice that (70%).

Because of this big drop in vaccine effectiveness, the study authors are recommending a booster dose for this age group.

 

AstraZeneca vs. Sinovac : Authors’ Conclusions

You can read the entire preprint paper, Effectiveness of Vaxzevria and CoronaVac vaccines in Brazil, by Cerqueira-Silva et. al.

Here are the conclusions by the study authors :

 

 

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