Scientists behind Oxford’s Com-COV2 study have endorsed the importance of COVID-19 booster vaccines after finding that antibodies dip significantly following primary doses of the AstraZeneca and Pfizer jabs

Vaccine being administered to older man tirachard

New UK data suggest that two doses of a COVID-19 vaccine induce lower levels of neutralising antibodies against the Omicron variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) than against previous strains.

The preliminary findings of a study conducted at the University of Oxford support the current strategy to offer third ‘booster’ jabs to as many adults as possible, experts from the University of Oxford have said.

Publication of the research came as Boris Johnson confirmed that a patient had died with Omicron in the UK—the first death recorded with the variant. It followed the Prime Minister’s television appeal for people to take advantage of an accelerated booster vaccine strategy.

Breakthrough infections

The preprint study found a substantial fall in neutralising antibody titres in people who had previously received two doses of either the AstraZeneca/Oxford University or Pfizer/BioNTech vaccine, with evidence of some recipients failing to neutralise at all.

The results indicate that the Omicron variant could drive an increase in breakthrough infections in previously infected or double-vaccinated individuals, which could result in a further wave of COVID-19 infections, scientists behind the Com-COV2 study said.

Using blood samples from people who had previously received two doses of the AstraZeneca or Pfizer vaccines, the researchers performed neutralisation assays using a live isolate of Omicron obtained from an infected person in the UK.

Antibody neutralisation titres against the Omicron variant were then compared with neutralisation against the Victoria strain of the first ‘wild-type’ SARS-CoV-2 virus, as well as against the Beta and Delta variants.

Neutralising titres in sera from participants who had received their second dose of the AstraZeneca vaccine 8–11 weeks previously had dropped to below the detectable threshold in all but one participant, the scientists reported.

Neutralising titres in sera from those who had received two doses of the Pfizer vaccine dropped 29.8-fold from 1609 against the Victoria strain to 54 against Omicron, with one participant dropping below the detection threshold, they said.

Matthew Snape, Professor of Paediatrics and Vaccinology at the University of Oxford and one of the study’s co-authors, said: ‘These data are important, but are only one part of the picture. They only look at neutralising antibodies after the second dose, but do not tell us about cellular immunity, and this will also be tested using stored samples once the assays are available.’

Although Omicron has the potential to produce a further wave of infection, there is currently no evidence of its effect on causing severe disease, driving up hospitalisation rates, or increasing mortality rates, authors of the study said.

Third-dose booster vaccinations

The authors concluded: ‘The impact of a third-dose vaccine is currently unknown, but may be expected to raise neutralisation titres against the new variant.’

However, Professor Snape told a briefing at the Science Media Centre that a rapid increase in infection rates from Omicron could put pressure on the health service.

He said: ‘If we have more people getting disease, even if individually they’re less likely to get severe disease, overall we’ll have many more people getting severe disease, and then you run into the issues with NHS capacity and so on.

‘So, I think that’s why it’s important, both at an individual level, but also at a kind of community level, to step forward for third doses to help avoid health systems being overwhelmed.’

Professor Teresa Lambe, of Oxford’s Jenner Institute, said: ‘I’m still very hopeful that our vaccines will protect us against severe disease and hospitalisation.’

However, it was prudent ‘to prepare for the worst and hope for the best’, she added.

Commenting on the paper, which has yet to be peer-reviewed, Penny Ward, Visiting Professor of Pharmaceutical Medicine at King’s College London, said that it would be helpful to have data from the COV-BOOST trial on neutralising antibody titres provided by the BNT162b (Pfizer) booster jab given to people who had received two doses of the ChAdOx01 (AstraZeneca) vaccine.

‘This information would be the more important, given that the majority of the more vulnerable older population in the UK were given a ChAdOx01 primary course and are now receiving their BNT162b booster shots,’ she said.

The Com-COV2 study also said that displacement of Delta by Omicron could make it necessary to produce vaccines tailored to the new variant. However, the authors cautioned that, because of the antigenic distance of Omicron, these might be unlikely to give protection against previous strains.

A viable alternative might be to switch from current monovalent vaccines to multivalent formulations, as is the practice in seasonal influenza jabs, they said.

This article was originally published on Medscape, part of the Medscape Professional Network.

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