Poor glycaemic control is associated with reduced response to COVID-19 vaccination

Poor glycaemic control has previously been shown to increase mortality risk in people with type 1 diabetes who contract COVID-19. The present study, conducted at a single centre in Rome between April and November 2021, sought to assess whether glycaemic control was associated with antibody response to SARS-CoV-2 vaccination.

Twenty-six adults with type 1 diabetes (mean age 40 years; mean diabetes duration 22 years) received two doses of the Pfizer/BioNTec mRNA vaccine 3 weeks apart and were followed up to 180 days after the initial dose. Immunoglobulin G (IgG) antibodies to the spike protein were assessed just before the first and second vaccine doses, 2 weeks after the second dose, and 90 and 180 days after baseline. Glycaemic control was assessed by HbA_1c at baseline and, in 13 participants, by CGM (at each time point) according to the international consensus on time in range (TIR) and time above range (TAR).

All participants tested negative to the anti-spike IgG at baseline. After vaccination, IgG levels peaked at 2 weeks after the second dose and gradually fell thereafter. Unlike in some previous studies, CGM-assessed glucose profiles did not change significantly in response to the vaccine.

Post-vaccine IgG was not significantly associated with HbA_1c at baseline. In contrast, however, baseline TIR (r=0.75; P=0.02) and TAR (r=­–0.82; P=0.008) were significantly associated with post-vaccine IgG response. Participants who met the recommended targets of ≥70% TIR and ≤25% TAR at baseline had significantly stronger titres of neutralizing antibodies, regardless of baseline HbA_1c. Weaker, but still significant, associations between CGM metrics at later time points and IgG levels were also observed.

The authors conclude that, although HbA_1c was not significantly associated with response to the SARS-CoV-2 vaccine, a better CGM profile prior to vaccination is associated with a greater IgG and neutralising antibody response, which highlights a role for good glycaemic control in vaccination efficacy.

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