Even vulnerable people, who are at risk of severe COVID-19, achieved good antibody levels after three doses of mRNA vaccine. This is shown by a study from the University of Gothenburg on patients having undergone a bone marrow transplant or with liver disease, including cirrhosis.

The aim of the study, which has been published in the journal Infectious Diseases, was to investigate the effects of repeated vaccinations and hybrid immunity against COVID-19 among particularly vulnerable individuals. Hybrid immunity refers to the protection provided by vaccination in combination with SARS-CoV-2 infection.

The results demonstrate how levels of COVID-19 antibodies build up following each successive vaccine dose in those with a fundamentally deficient immune defense. This is a field where there remains limited knowledge.

Equivalent after the third dose

The study included 38 patients with liver cirrhosis, 36 bone marrow transplant recipients, 14 patients with autoimmune liver disease, and 20 healthy controls. All patients were cared for at Sahlgrenska University Hospital in Gothenburg, Sweden.

The patients were monitored for COVID-19 antibodies after their first, second, third, and for some bone marrow transplant recipients, their fourth vaccine doses. None of the participants had had COVID-19 before the second dose, but 31 of them had a mild COVID-19 omicron variant infection between the second and third doses.

Those with deficient immune defense due to liver disease or having received a bone marrow transplant had less protection than the controls up until after the second dose of the vaccine. Following the third dose, however, the groups had equivalent levels of antibodies.

Regardless of their level of underlying immunity, all groups included in the study showed antibody levels that were ten times higher after COVID-19 infection compared to those who had acquired their immunity through vaccination alone.

Unexpectedly good protection among the vulnerable

Three doses of mRNA vaccine against COVID-19 thus resulted in high antibody concentrations even in immunocompromised individuals, and hybrid immunity resulted in even higher levels.

Martin Lagging is a Professor in Clinical Virology at the University of Gothenburg's Sahlgrenska Academy, a senior physician at Sahlgrenska University Hospital, and the study's last author.

"It was unexpected—but extremely pleasing—to note that vulnerable individuals achieved antibody levels on a par with the healthy ones after three doses of vaccine," he explains. "This underlines the importance of continuing to vaccinate, even if the immune response is poor after the first doses."