COVID-19: Antibody Limits Under Discussion

How high do antibody titres have to be in order to be protected from COVID-19 infection after a corona vaccination? This question is still currently subject of much discussion. So far, there is no defined limit value on the basis of which the protective effect can be read. Accordingly, there is also no index that indicates when the immune response is no longer sufficient to become ill with COVID-19 after a SARS-CoV-2 infection.

However, this information would be of particular interest with regard to third-party or booster vaccinations. Researchers from the University of Oxford have recently presented limit values as immune correlation; the results of their study can be read in the journal Nature Medicine.

In addition, defined limit values form an evidence base for vaccination recommendations, for example for booster vaccinations. Against this background, a scientific team led by Dr. Shuo Feng from the University of Oxford determined in a continuation of the pivotal study of Vaxzevria how high the antibody levels must be after primary immunization in order to effectively prevent COVID-19 infection.

In this research, researchers looked at the antibody titres of people who were vaccinated twice with AstraZeneca’s COVID-19 vaccine. More precisely, they determined the binding and neutralizing antibodies 28 days after the second dose in infected and non-infected vaccine recipients. To demonstrate the efficacy of vaccination, the threshold values for four immune markers (anti-spike IgG, IgG antibodies against the receptor-binding domain [RBD], pseudovirus neutralization and live corona virus neutralization) associated with protection against symptomatic infection were determined.

Among the 4,372 participants in the correlate population, there were a total of 174 breakthrough cases of SARS-CoV-2 infection. As a result, higher levels of all immune markers were associated with a lower risk of symptomatic COVID-19 disease.

According to the results, an 80 percent protective effect against symptomatic infection with the alpha variant of SARS-CoV-2 is achieved with 264 binding antibody units (BAU)/ml of IgG antibodies directed against the spike protein of SARS-CoV-2 and 506 BAU/ml for anti-RBD antibodies, according to the study authors.

 

Reference

https://doi.org/10.1101/2021.06.21.21258528