How well do the Pfizer and Sinovac vaccines work against the Omicron variant? Not very well, I’m afraid.
Take a look at what a small HKU study just revealed!
Pfizer / Sinovac vs. Omicron : How Was HKU Study Conducted?
The University of Hong Kong recently conducted a small lab study to investigate how well the Pfizer and Sinovac vaccines work against the new Omicron variant of COVID-19.
Before I go into the study results, it is important that you understand how they conducted their study. You can also read their preprint.
The HKU team took blood samples from two groups of people who received their first dose 56 days earlier :
- 25 people who received two doses of the Pfizer-BioNTech COMIRNATY vaccine
- 25 people who received two doses of the Sinovac CoronaVac vaccine
They removed all cells and clotting factors from the blood samples, to derive the serum which would contain neutralising antibodies.
The HKU team then used the 50 serum samples to assess their ability to neutralise :
- Omicron variant from South Africa (HKU691)
- Omicron variant from Nigeria with additional R346K mutation (HKU344-R346K)
- Alpha, Beta and Delta variants (as controls)
They basically mixed the serum with the virus sample for an hour, and then added the mixture to a Vero cell culture for 3 days, before examining them to see if the cells were infected and destroyed.
Pfizer / Sinovac vs. Omicron : What HKU Study Just Revealed!
The problem with most of the reporting I’ve read is that – the writers did not actually read the preprint, only the HKU press release.
Not only did they miss a ton of details, they also missed some important points. So let me start by first summarising what the HKU team found in this table :
| COVID-19 Variant |
Seropositive Rate | MN Titer (GMT) | ||
| Pfizer | Sinovac | Pfizer | Sinovac | |
| HKU691 Omicron | 20% | 0% | 5.43 | Min. |
| HKU344-R346K Omicron |
24% | 0% | 6.42 | Min. |
| Delta | 100% | 68% | 124.7 | 10.3 |
| Beta | 100% | 0% | 25.7 | Min. |
| Alpha | 100% | 100% | 229.4 | 21.7 |
Also, take a look at the geometric mean titre (GMT) of Microneutralisation (MN) antibodies provided by the HKU team :
So what does this HKU study tell us? Let me summarise the key takeaway points :
Pfizer-BioNTech COMIRNATY Vaccine
- Pfizer vaccine antibodies were able to bind to the Omicron variant in 20% to 24% of samples.
- Pfizer vaccine antibodies were able to bind to Alpha, Beta and Delta variants in 100% of samples.
- Pfizer neutralisation antibody titres were highest against Alpha and Delta variants.
The results suggest that mutations in its spike protein are allowing the Omicron variant to significantly block Pfizer vaccine antibodies.
There is some protection from the Pfizer vaccine antibodies, but a third dose is necessary to boost the neutralising antibody response against the Omicron variant.
The good news is that the study shows that the Pfizer vaccine is excellent at neutralising the Alpha and Delta variants.
Sinovac CoronaVac Vaccine
- Sinovac vaccine antibodies were completely unable to bind to both Omicron variants, as well as the Beta variant.
- Sinovac vaccine antibodies were able to bind to 100% of the Alpha variant samples, but only 68% of the Delta variant samples.
- Sinovac neutralisation antibody titres were highest against Alpha and Delta variants, but were 10.5X to 12X lower than the Pfizer titres respectively.
The results suggest that the Omicron variant can completely evade neutralising antibodies produced by the Sinovac vaccine.
That’s why the HKU study authors concluded that “whether a third dose of the present CoronaVac vaccine will enhance the neutralising antibody response against the Omicron variant remains to be determined.”
The results also confirm yet again that the Sinovac CoronaVac vaccine is far less efficacious than the Pfizer-BioNTech COMIRNATY vaccine across the board.
CAVEATS
As interesting as the HKU study results are, there are a few caveats we should be aware of :
- This is a very small study
- This is an in vitro (laboratory) study, and not a real world study
- It only assessed neutralising antibodies in the serum, and does not assess T cell immunity
Pfizer / Sinovac vs. Omicron Results : What Should You Do?
For scientists, these alarming results suggest a need for the COVID-19 vaccines to be tweaked or updated to cover the Omicron variant.
For the rest of us, it means we need to take a booster dose as soon as we are able to. The HKU team ended their study with the same advice :
[B]efore the availability of these next generation vaccines, booster doses of currently available vaccines will likely render most people having protective levels of neutralizing antibody titers.
But it is also not just getting a third dose, but a booster dose of a better vaccine. This is especially important if you earlier received a less efficacious COVID-19 vaccine like the Sinovac CoronaVac.
Those who had earlier received the Sinovac vaccine should heed these results, and opt for a Pfizer or Moderna booster dose, as recommended by many health authorities.
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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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