[Okayama University] Utility of Viral Antibody Titer Measurement in Long COVID Care during the Omicron Period ~Brain Fog Symptoms and Decreased QOL Associated with Antibody Titers~

May 6, 2026 National University Corporation Okayama University

https://www.okayama-u.ac.jp/

<Key Points of the Announcement>

In the treatment of post-COVID-19 conditions (long COVID), objective biomarkers are needed to evaluate disease activity and prognosis.

Analysis of blood coronavirus antibody titers in long COVID patients infected during the Omicron variant period revealed that brain fog symptoms and decreased QOL were associated with low anti-spike (S) antibody levels. On the other hand, anti-nucleocapsid (N) antibodies were found to be high in females and in cases that were severe at the time of infection, and to decay at a certain rate over time after infection.

Knowing the fluctuations in viral antibody titers in long COVID care was considered useful for predicting the prognosis of long COVID and the history of Omicron-period COVID infection, which is difficult to objectively ascertain.

◆Overview

Long COVID symptoms such as fatigue, headache, insomnia, and memory impairment persist for a long time, making it an ongoing medical and social challenge. Since long COVID symptoms are primarily subjective, indicators (biomarkers) that can objectively evaluate the disease state and severity are required. Furthermore, it is thought that the symptoms and disease activity of long COVID may fluctuate with changes in viral variants.

A group led by Assistant Professor Marina Kawaguchi (Specially Appointed) of the Department of General Internal Medicine and Community Healthcare, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences (Medicine), Okayama University, Dr. Yasue Sakurada of the Department of General Internal Medicine and General Practice, Okayama University Hospital, and Professor Fumio Otsuka of the Department of General Internal Medicine, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences (Medicine), National University Corporation Okayama University (Headquarters: Kita-ku, Okayama City; President: Yasutomo Nasu), targeted 275 long COVID patients (146 females, 129 males; median age 41) who visited the COVID Aftercare Clinic (long COVID clinic) at Okayama University Hospital between July 2023 and November 2024. They measured the antibody titers (concentrations) of anti-spike (S) antibodies and anti-nucleocapsid (N) antibodies against the SARS-CoV-2 virus present in serum and analyzed their association with clinical symptoms and background factors. The presence of blood S antibodies reflects both vaccination history and COVID infection history, while the presence of N antibodies reflects only natural COVID infection history.

As a result, blood S antibody titers in long COVID patients were high in association with the number of vaccine doses and decreased over time. On the other hand, blood N antibody titers were high in long COVID patients with severe infection at the time of infection and in female patients, and were shown to decrease at a certain rate over time after coronavirus infection.

Furthermore, long COVID patients with low blood S antibody titers showed symptoms of brain fog and decreased quality of life (QOL). From these results, it is considered possible to objectively evaluate the background of the acute phase of COVID infection and the characteristics of long COVID symptoms by evaluating both S and N antibody titers, and their application to future diagnosis and pathological understanding is expected.

These research results were published on April 22, 2026, in the international academic journal "British Journal of Biomedical Science."

Figure 1. Association between long COVID symptoms and SARS-CoV-2 antibody titers Box plot showing the comparison of S antibody titers based on the presence or absence of each symptom. Mann–Whitney U test was used for comparison. Significance level was P < 0.01(**).

◆A word from the researchers

<Assistant Professor Marina Kawaguchi>

I believe it is an interesting result that the relationship between the immune response after infection and memory impairment (brain fog) and decreased quality of life has been suggested. I hope this will contribute to elucidating the pathology of brain fog in long COVID.

<Dr. Yasue Sakurada>

We have obtained results that bring us closer to elucidating the pathology of long COVID and establishing biomarkers. We will continue to create evidence that can contribute to the recovery of patients.

<Professor Fumio Otsuka>

Although the number of COVID-19 patients themselves has decreased, many patients are still undergoing treatment for long COVID. We feel the need to continue clinical practice and research related to long COVID.

◆Paper Information

Title: Clinical utility of SARS-CoV-2 antibody titers in the management of patients with long COVID infected with the Omicron variant Journal: British Journal of Biomedical Science 83:16255, 2026. Authors: Marina Kawaguchi, Yasue Sakurada, Kazuki Tokumasu, Yuki Otsuka, Yasuhiro Nakano, Yui Matsuda, Hir