Omicron: 2 doses of Sinopharm vaccine offers weak protection against new strain, finds study

Researchers from the University of Washington and Humabs BioMed investigated how Omicron might escape immunity from past infections or vaccination
Research confirms recent studies finding mutations on the receptor-binding domain of the spike protein led to immunity escape against available vaccines

Coronavirus pandemic

Zhuang Pinghuiin Beijing

Published: 7:00am, 17 Dec 2021

Why you can trust SCMP

The Omicron variant of the coronavirus evades immunity offered by an inactivated Covid-19 vaccine developed by Sinopharm, a lab study has found.

Researchers from the University of Washington and Swiss antibody therapeutics company Humabs BioMed investigated how the Omicron variant might escape immunity from past infections or vaccination by comparing the performance of plasma from recovered Covid-19 patients and people vaccinated with six major Covid-19 vaccines.

They tested how the plasma worked against a pseudovirus genetically modified to resemble the ancestral and Omicron variants of the virus that causes Covid-19. The results of the study, which were not peer-reviewed, were published on BioRxiv.org.

01:53

China records second Omicron case, further tightens measures to contain latest Covid-19 outbreaks

Results showed the antibody levels of people vaccinated with Sinopharm’s vaccine dropped significantly against Omicron compared with the ancestral, or older, strain and, of the total 13 participants, only three people could be found to produce detectable antibodies that could block the Omicron strain of the virus from entering cells, a process known as “neutralising”.

David Veesler, associate professor at the department of biochemistry at the University of Washington and one of the correspondence authors of the study, said the in vitro studies evaluated plasma neutralising antibodies “which is a correlate of protection against Sars-CoV-2”, the virus that causes Covid-19.

“However, other factors such as T cells [an immune system cell] can play important roles to protect us against pathogens, especially in the absence of neutralising antibodies,” Veesler said.

“It is accurate to say that we could not detect plasma neutralising activity against Omicron in most Sinopharm vaccines. Evaluating vaccine-efficacy in the human population will require epidemiology studies.”

Boosters work, no need for Omicron-specific jabs, says disease expert Fauci

A drop in effectiveness against Omicron was observed in all six vaccines tested, but participants vaccinated with Moderna, Pfizer and AstraZeneca vaccines displayed higher levels of neutralising antibodies against the ancestral strain and, after a 33-44-fold drop they still had detectable neutralising antibodies against the Omicron variant.

Only one out of 12 participants administered with the one-shot Johnson & Johnson was shown to have neutralising activity but none from the 11 subjects injected with the Sputnik vaccine.

It confirmed a flurry of studies that found the mutations on the receptor-binding domain of the Omicron’s spike protein – the part of the coronavirus that docks on to human cells, initiates infection and targets of most Covid-19 vaccines – led to immunity escape against available vaccines, including those produced by Moderna and Pfizer.

Governments around the world are scrambling to offer booster doses to prepare for the potential wave of infections caused by the Omicron variant, which the World Health Organization warns is likely to take over from Delta as the dominant strain in community spread.

The study follows a similar one conducted by the University of Hong Kong, which showed that two doses of Sinovac, the Covid-19 vaccine most used in the world, could not prevent infection from the Omicron variant. It also offered a rare glimpse into the effectiveness of vaccines widely used in low-income countries but less studied than mRNA vaccines.

06:14

Why is the Omicron variant so concerning? Virologist warns Covid strain could ‘wreak havoc’ in HK

Meanwhile, less than a quarter of participants who received two doses of Pfizer could produce antibodies to neutralise Omicron.

Sinovac said in a statement three doses would produce antibodies that could prevent infection from the new variant.

Dr Mike Ryan, head of the WHO’s Health Emergency Programme, said on Tuesday that a drop-off in the ability to prevent infection over time was always expected, especially with a mucosal infection such as Covid-19.

“The question is, to what extent do we see any loss in protection beyond neutralising antibodies and looking at other immunologic markers and then looking at the real-world,” he said.

Last week Zhang Yuntao, chief scientist with China National Biotec Group, a subsidiary of Sinopharm which developed the Covid-19 vaccines, said the company had started designing Omicron-specific vaccines in three different technology platforms, although Zhang did not elaborate.

Covax chief warns against replay of Covid-19 vaccine nationalism

The Gamaleya Centre, which developed Russia’s Sputnik V vaccine, said in a statement on Monday that the serum samples used in the study were “not representative” and the centre would publish its own “positive data” in a week.

Johnson & Johnson said last month it was testing blood serum from participants in completed and continuing booster studies to look for neutralising activity against the Omicron variant, and pursuing an Omicron-specific variant vaccine.