Third Shot Of MRNA COVID-19 Vaccine Helps Immunocompromised
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Haemodialysis patients produce a larger neutralizing antibody response against the Pfizer-BioNTech COVID-19 vaccine versus the Oxford-AstraZeneca vaccine, show laboratory findings published as a Correspondence in The Lancet. Levels of antibodies alone do not predict vaccine effectiveness and researchers are confident that for most, a complete course of either vaccine will still protect against severe disease or death.

It is reported that immunocompromised patients will be prioritised to receive a third dose of vaccine in the autumn, so researchers have submitted their findings to the Joint Committee on Vaccination and Immunisation (JCVI) as evidence of how best to protect this vulnerable group. As part of the study, the research team examined blood samples from 178 patients receiving haemodialysis treatment.

The researchers used robust high throughput viral neutralisation assays (laboratory tests), developed at the Crick, to test the ability of antibodies to block entry of the virus into cells, so called 'neutralising antibodies', against different variants of SARS-CoV-2, including Delta. In patients who had not been previously infected with SARS-CoV-2, those who had received the Pfizer-BioNTech mRNA vaccine had six-times higher levels of neutralising antibodies against the Delta variant, compared to those vaccinated with the Oxford-AstraZeneca vaccine.

The levels induced by the mRNA vaccine were comparable to those seen in healthy controls after both vaccine doses. In patients who had evidence of infection prior to vaccination, both vaccines induced detectable levels of neutralising antibodies. These findings suggest that patients who have not been infected with SARS-CoV-2 previously and received the Oxford-AstraZeneca vaccine, would likely benefit from an early third dose of an alternative mRNA vaccine.

"These findings clearly indicate that dialysis patients are unlikely to be adequately protected from the delta variant if they received the AZ vaccine. Researchers believe that this study provides strong evidence to support a third dose of an mRNA vaccine as standard treatment as soon as possible for all immunocompromised patients who potentially remain at risk."