Is Sinovac + Pfizer Combo Less Effective Against Omicron?

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Was the combination of Sinovac and Pfizer proven to be less effective against the Omicron variant of COVID-19?

Let’s take a look at the claim, and find out what the facts really are!


Claim : Sinovac + Pfizer Combo Proven Less Effective Against Omicron

On 9 February 2022, The Edge posted an article with the title “Combination of Sinovac and Pfizer proven less effective to fight Omicron, says Pharmaniaga“.

The article covers Pharmaniaga’s statement which suggested that a third dose of Sinovac (of which they are the licensed distributor) is better than the Pfizer booster dose.

Let me share the relevant parts of the article, with key segments in bold. It’s a long read, so you can skip to the next section for the facts.

Pharmaniaga Bhd, citing a study conducted by Yale University, said that two doses of Sinovac Covid-19 vaccine with a Pfizer-BioNTech booster dose are less effective and produces a lower immune response against the Omicron variant compared with other strains.

On the other hand, Pharmaniaga, which is the licensed distributor of Sinovac vaccine in Malaysia, highlighted that a separate research by Sinovac Biotech Ltd shows that three doses of Sinovac Covid-19 vaccine produced higher neutralising antibodies in 95% of recipients compared with 3.3% by the second dose against a variant of concern (VOC), including Omicron.

Is Sinovac + Pfizer Combo Less Effective Against Omicron?


Truth : Pfizer Booster Is Superior To Sinovac Booster Against Omicron

I have not read the actual Pharmaniaga statement, because it is still not available on their website.

However, I had earlier written about the Yale University study, and the statement as shared by The Edge appears to misrepresent what the study actually said.

It also appears to ignore what other studies have said about the poor efficacy of the Sinovac vaccine, including their own Phase 3 trial results.

Let’s go through the claims, and see what the facts really are…

Fact #1 : All Vaccines Are Less Effective Against Omicron

Because it has so many mutations, the Omicron variant is more able to escape the antibody protection that vaccines offer. This is true for all COVID-19 vaccines, not just the Pfizer vaccine.

It seems rather disingenuous for Pharmaniaga to point out that the Pfizer booster dose is less effective against Omicron, compared to other variants… when that is the case for all other vaccines, including Sinovac.

Fact #2 : Booster Dose Will Always Raise Antibody Levels

A booster dose is like a refresher course for your immune system. It will always boost antibody levels against COVID-19.

So the “separate research by Sinovac” themselves (instead of a neutral third party) only tells us that their booster dose is doing what other booster doses are doing – increasing antibody levels.

Abuthen? Did you expect a different result?

Fact #3 : What They Didn’t Say Is Interesting…

You can pick up more information if you note what Pharmaniaga did not say, assuming The Edge did not leave out anything pertinent.

For example, Pharmaniaga did not mention how much was the increase in antibody levels. Why not?

Neither did they confirm that the higher level was sufficient to protect against the Omicron variant. Why not?

They also conspicuously did not claim that the Sinovac booster dose is more effective than the Pfizer booster dose against the Omicron variant. Why not?

Fact #4 : Pfizer Booster Greatly Improves Protection

The Yale University study showed that two doses of Sinovac with a Pfizer booster dose gives protection equivalent to two mRNA vaccine doses.

However, the Pharmaniaga statement left out the very pertinent fact of what that actually meant :

  • 10.1X higher NAb levels against ancestral (original) virus : 
  • 6.3X higher NAb levels against Delta variant : 

The study also showed that two doses of Sinovac with a Pfizer booster offered 40% better protection against Omicron than two doses of the mRNA vaccines.

In other words, the Pfizer booster dose greatly improves on the mediocre protection offered by the Sinovac vaccine, but it may not be at par with 3-doses of other vaccines.

Read more : Why Sinovac Recipients May Need Two Pfizer Booster Doses!

Pfizer / Sinovac vs. Omicron : What Did HKU Study Reveal?

Fact #5 : Cross Protection Not Seen With Sinovac Vaccine

According to Pharmaniaga, the Yale University study showed that no cross protection (hybrid immunity) was seen in Sinovac recipients who receive a Pfizer booster dose.

That is absolutely correct, but it does not mean what they think it means.

Professor Iwasaki specifically pointed out, “Prior infection only synergies with the mRNA vax to elevate broadly neutralizing Ab but not with inactivated vax. This may relate to the persistent GC (Germinal Centre) responses in mRNA vax”.

In other words, this synergistic boost in antibody levels from a COVID-19 infection is only seen with mRNA vaccines like the Pfizer COMIRNATY, but not seen with inactivated virus vaccines like the Sinovac vaccine.

Let me put it plainly – the Yale study showed that if you want cross protection (hybrid immunity), you will get it with the Pfizer vaccine, but not with the Sinovac vaccine.

Fact #6 : Pfizer Superior To Sinovac Against Beta, Delta + Omicron

A recent Hong Kong University (HKU) study showed that while the Pfizer vaccine is less effective against Omicron, the Sinovac vaccine is worse.

  • Sinovac vaccine antibodies were completely unable to bind to the Beta and Omicron variants.
  • Sinovac vaccine antibodies were only able to bind to the Delta variant in 68% of individuals.

Read more : Pfizer / Sinovac vs. Omicron : What HKU Study Just Revealed!

Seropositive Rate
Pfizer Sinovac
Alpha 100% 100%
Beta 100% 0%
Delta 100% 68%
Omicron 20% – 24% 0%

Incidentally, the Yale University study also pointed out that there was NO detectable neutralisation against the Omicron variant in people who received two doses of the Sinovac vaccine.

Even Pharmaniaga themselves inadvertently confirmed it, when their statement mentioned that only 3.3% of people vaccinated with 2 doses of Sinovac had neutralising antibodies against variants including Omicron.

Fact #7 : 3X Sinovac Doses Not Sufficient Against Omicron

A joint study by Hong Kong University (HKU) and the Chinese University of Hong Kong (CUHK) recently showed that 3 doses of the Sinovac vaccine does not provide sufficient protection against Omicron.

  • Three doses of the Pfizer vaccine offer the highest level of protection against Omicron.
  • A Pfizer booster dose given to those who received two Sinovac vaccine doses obtain good protective antibody levels against Omicron.
  • Three doses of the Sinovac vaccine do not provide sufficient protection against the Omicron variant.
  • Antibody levels of three doses of the Sinovac vaccine were roughly equal to two doses of the Pfizer vaccine.

Read more : Pfizer vs. Sinovac : Which Is Better Against Omicron Variant?

Pfizer vs Sinovac Booster Dose Omicron study results

Fact #8 : Sinovac Is Least Efficacious COVID-19 Vaccine

The Sinovac CoronaVac is the least efficacious COVID-19 vaccine, barely qualifying for its EUA/EUL with a 50.4% efficacy rate in its Phase 3 trial.

Back when vaccine supply was extremely limited, some protection was better than nothing at all, which is why health authorities deployed the Sinovac vaccine.

Now that we have supplies of better vaccines – Pfizer, AstraZeneca, Sinopharm, etc., there is no longer any reason to settle for the Sinovac CoronaVac.

It is impossible for the Sinovac vaccine to improve its efficacy against the ancestral (original) COVID-19 virus, and it is certainly ludicrous to suggest that a third dose will boost its efficacy from 50.4% to 94%.

Please listen to advice from health authorities, instead of a vaccine manufacturer and/or its distributor.

CITF-B strongly recommends the Pfizer or AstraZeneca booster dose for Sinovac recipients, because they offer better protection.

Sinovac recipients are at the highest risk of a breakthrough infection, because they have the least protection. So make sure you get the best booster dose you can!


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Dr. Adrian Wong has been writing about tech and science since 1997, even publishing a book with Prentice Hall called Breaking Through The BIOS Barrier (ISBN 978-0131455368) while in medical school.

He continues to devote countless hours every day writing about tech, medicine and science, in his pursuit of facts in a post-truth world.


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