The third dose of a COVID-19 mRNA vaccine boosts serologic and cellular memory response in patients on hemodialysis who were never infected with SARS-CoV-2, but not in those previously infected with the virus, a new study finds.

Among 59 patients on hemodialysis who received the Pfizer mRNA vaccine at 3 dialysis centers in France, 33 were never infected and 26 had recovered from SARS-CoV-2. Among a control group of 49 adults without kidney disease, 23 were never infected and 26 had recovered. All patients received standard 2-dose vaccination followed by a third dose within 6 months. The investigators assessed anti-receptor binding domain immunoglobulin G (IgG) titers and memory B cells after the second and third dose. Response in healthy individuals after 2 doses was used as the reference.

Antibody Response

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Among virus-naive patients, IgG response was numerically lower after 2 doses but significantly increased 3-fold after the third dose in those on hemodialysis compared with healthy individuals who had standard vaccination, corresponding author Khalil El Karoui, MD, PhD, of Assistance Publique-Hôpitaux de Paris in France and colleagues reported in the Clinical Journal of the American Society of Nephrology. Among SARS-CoV-2-recovered patients, IgG titers after 2 doses rose significantly higher in those on hemodialysis compared with healthy individuals but did not increase further after a third dose.

Memory B cell response

Among virus-naive patients, memory B cell response after 2 doses was comparable between those on hemodialysis and healthy individuals. After the third dose, memory response significantly increased 5.5-fold in patients on hemodialysis compared with the reference group.

SARS-CoV-2-recovered patients on hemodialysis, however, had no greater memory response after the second or third dose, compared with the reference group.

According to Dr El Karoui’s team, the findings suggest that virus-naive patients on hemodialysis “do not have a maximal immune response (antibodies as well as memory B cells) after two doses, and therefore, a third dose can have a booster effect.” In SARS-CoV-2-recovered patients, “the immune response is already maximally activated after infection and two doses, and therefore, a third dose given within 6 months may have no additional booster effect.”

Whether a third dose given later than 6 months results in similar or different responses still needs to be studied. The neutralizing capacity of memory B cells in the dialysis population also requires further investigation.

“These results suggest that the timing of the third dose and a previous SARS-CoV-2 infection have a critical effect in vaccine response of patients on dialysis and should be considered in future vaccine policies of this population.”

Disclosure: Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.


Attias P, Azzaoui I, El Karoui K, et al. Immune responses after a third dose of mRNA vaccine differ in virus-naive versus SARS-CoV-2-recovered dialysis patients. Clin J Am Soc Nephrol. Published online June 28, 2022. doi:10.2215/CJN.00830122