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Moderna COVID-19 vaccine and antibody response to variants of concern (Alpha, Beta, Gamma, Epsilon, Iota and Delta)

This article was published on
August 13, 2021

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New data has been released on the ability of the Moderna COVID-19 vaccine to generate neutralising antibodies against variants of concern. The paper, published in Science found that most people vaccinated with the Moderna COVID-19 vaccine maintained both binding and functional antibodies against SARS-CoV-2 variants for six months after the second dose.

New data has been released on the ability of the Moderna COVID-19 vaccine to generate neutralising antibodies against variants of concern. The paper, published in Science found that most people vaccinated with the Moderna COVID-19 vaccine maintained both binding and functional antibodies against SARS-CoV-2 variants for six months after the second dose.

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Durability of mRNA-1273 vaccine–induced antibodies against SARS-CoV-2 variants

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Expert Comments: 

Dr Peter English

This paper reports on studies undertaken with a small number (24) of volunteers from the  vaccine trials.

As with previous such reports, the number of study subjects is very small compared to vaccine efficacy or effectiveness studies (which often use thousands or tens of thousands of subjects); but because detailed observations are acquired from each subject, and all the outcomes are of interest, this does not invalidate the findings.

The study looked primarily at “neutralising antibodies” – the level of antibodies which are able to bind to and neutralise viral spike proteins; and at how this varied with different viral variants and over time.  Because it was a laboratory based study, they will have been able to obtain data from each subject on these factors.

While such findings are very interesting, and will help inform decisions about whether and when booster vaccination might be worthwhile, we do not yet have clear “correlates of protection”: we don’t know if there is an antibody threshold, below which protection is lost.

Other factors are also important.  Cellular immunity (including e.g. T-cells, memory cells) is much harder to measure, but can mean that individuals have “immune memory” – so that, even if antibody levels have dropped, they will very rapidly be able to boost their antibody levels on exposure to the virus; and there may also be further maturation of the immune system which might lead to greater cross-protection against other variants.  It is possible to have excellent protection against infection (and certainly against serious illness), even with extremely low antibody levels.  This means that this sort of laboratory study has to be supported by observational studies of vaccine effectiveness.  Useful summaries of such work, to date, are published regularly by Public Health England1.

I am reassured by these findings that there is cross-protection against variant strains (and this is backed up by other real-world effectiveness studies); and that the while the protection afforded by antibodies alone may have reduced over the study period, it has not yet disappeared.

1. Public Health England. COVID-19 vaccine surveillance report: 12 August 2021 (week 32). COVID-19 vaccine surveillance reports 2021; Updated 12 Aug 2021; Accessed: 2021 (13 Aug): (https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1010472/Vaccine_surveillance_report_-_week_32.pdf or via https://www.gov.uk/government/publications/covid-19-vaccine-surveillance-report).

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