Do current COVID-19 vaccines and treatments neutralise Omicron?

Scientists around the world have rapidly worked to develop and identify a number of vaccines and treatments for COVID-19 in a relatively short time.
 
However, when a new variant emerges, data on efficacy is thrown into question.
 
When compared to the original strain of SARS-CoV-2, Omicron has 36 mutations in the spike protein, which facilitates entry into host cells, impacting the protection offered by currently available vaccines.
 
But new research led by the University of Cambridge is offering some reassurance.
 
Published in the journal Nature, the research team incubated both live and pseudoviral particles with clinically approved antibodies to analyse the interactions between the antibodies and the Omicron spike.
 
Promisingly, the antiviral agents remdesivir and molnupiravir were both shown to have similar activity against the Delta and Omicron variants.
 
Remdesivir, which was the first COVID-19 treatment to be approved by the Therapeutic Goods’ Administration (TGA) for use in Australia, is recommended for use by Australia’s National COVID-19 Clinical Evidence Taskforce (the Taskforce) in adults who are hospitalised with COVID-19 and require oxygen, but who do not require ventilation.
 
Molnupiravir on the other hand, was only approved by the TGA last month, but is among the treatments that will be available for GPs to prescribe, particularly for patients deemed to be at high risk of developing severe disease.
 
The researchers also tested casivirimab and imdevimab, a combined monoclonal treatment approved for use in Australia, which proved particularly effective at neutralising Delta. However, the treatments were found to lose all neutralising activity against Omicron when used either individually or in combination.
 
Dr Marguerite Tracy, a member of the RACGP Expert Committee – Quality Care (REC–QC), told newsGP that the findings are ‘reassuring’, but highlighted that there may be limitations due to it being a lab-based study.
 
‘With Omicron BA.2 now with us, data on the efficacy of treatments will be vital in ensuring the treatments we are using remain effective,’ she said.
 
‘GPs having access to antiviral medications which are effective in preventing serious disease in vulnerable members of the community will mean less illness and death from COVID-19 and reduce the pressure on tertiary healthcare.’
 
Sydney GP Dr Michael Tam, who is also a member of the REC–QC, agrees.
 
‘This is excellent news,’ he told newsGP.
 
‘Moving forward, improved and rapid access to effective antiviral treatment will be an important part of normalising “living with COVID-19”.’ 
 
What about vaccination?
While current vaccines have reduced efficacy against Omicron, the UK research provides reassurance on the importance of a booster dose.
 
To determine the effectiveness of existing vaccines against the variant, the team produced virus particles expressing the spike protein from both Delta and Omicron, and exposed them to serum from 40 individuals who had received two doses of either Pfizer or AstraZeneca.
 
Participants had a median age of 70 and it was either one month or six months since their second dose.
 
The findings show that after two doses of either vaccine, there is at least a 10-fold reduction in neutralisation of Omicron compared to Delta, with the waning efficacy increasing with the gap since the second dose. For those vaccinated with AstraZeneca, neutralisation of Omicron was not detectable at all for the majority.
 
However, when either cohort received a booster of Pfizer, neutralisation was found to increase more than 10-fold one month after the third dose.
 
Dr Tracy welcomed the findings but said emerging evidence about the importance of a third dose for protection against Omicron appears to render the term ‘booster’ inaccurate.
 
‘It is heartening that there is evidence that a third dose truly does provide protection,’ she said.
 
‘[But simultaneously] disheartening that the speed of uptake of “booster” doses in Australia has been much slower than the first two doses.
 
‘Omicron BA.1 has been less severe on average than Delta, although devastating in our aged care residents, [and] as a result the urgency that Australians felt to get vaccinated last year when Delta arrived does not seem to have translated action to a get a third dose to prevent Omicron infection.’
 
As part of ongoing efforts to determine the potential need for variant-based vaccines, Pfizer commenced a clinical trial with 1420 people last month to evaluate the safety, tolerability and immunogenicity of an Omicron-based vaccine candidate in adults. Moderna is making similar efforts, with a vaccine candidate for Omicron, with data expected to be sent to regulators in March.
 
Dr Kathrin Jansen, the Senior Vice President and Head of Vaccine Research and Development at Pfizer, said while there is evidence to show boosters provide a high level of protection against severe disease and hospitalisation with Omicron, there is still a need to be prepared for new variants.
 
‘Staying vigilant against the virus requires us to identify new approaches for people to maintain a high level of protection, and we believe developing and investigating variant-based vaccines, like this one, are essential in our efforts towards this goal,’ she said.
 
In the meantime, however, Dr Tracy said while it is not exactly known what will be needed to combat the next variant that the evidence on boosters – or third doses – is clear.
 
‘We do know that you need three doses to reduce transmission and severity of Omicron BA.1 infection,’ she said.
 
‘[But] general practice will need significant increased resourcing if practices are expected to implement recalls on top of implementing doses for 5–16[-year-olds] and adult “boosters”.’
 
Earlier this week, Federal Health Minister Greg Hunt flagged that the Australian Technical Advisory Group on Immunisations (ATAGI) is looking to change the definition of being fully vaccinated from two to three doses.
 
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AstraZeneca casivirimab COVID-19 Delta imdevimab molnupiravir Omicron Pfizer remdesivir vaccination