Clinical microbiology and infection : the official publication of the European Society of Clinical Microbiology and Infectious DiseasesJun 20, 2026

Two-Year Study Tracking COVID-19 Virus Protein Levels in People with Long COVID

Long Covid Weekly Brief ↗PubMed ↗DOI ↗

Updated Jun 22, 2026

Abstract

SARS-CoV-2 antigens were detected in plasma of 31% of individuals with Long COVID at 6-12 months post-infection.

At 6-12 months, 20% of fully recovered individuals and 5.4% of uninfected controls also had detectable SARS-CoV-2 antigenemia.
By 18-24 months, antigenemia positivity declined to 3% in Long COVID patients and dropped to 0% in both recovered and uninfected individuals.
The full spike protein was the most commonly detected antigen, while the S1 subunit was rarely observed and nucleocapsid was absent in recovered participants.
Antigenemia was not linked to the number or type of persistent symptoms, antibody levels, or vaccination status.
Current findings do not support the use of plasma SARS-CoV-2 antigens for clinical monitoring or treatment decisions in Long COVID.

Simplified

OBJECTIVES: SARS-CoV-2 antigens have been detected in plasma months after acute infection, but their long-term dynamics and clinical relevance remain unclear. We aimed to assess the persistence and clinical specificity of plasma SARS-CoV-2 antigenemia over two years following acute infection.

METHODS: We conducted a 2-year longitudinal study involving 425 adults who developed Long COVID (n=167) or fully recovered from acute Covid-19 (n=148), and uninfected controls (n=110). Plasma samples were collected at 6-12 months and 18-24 months post-infection. SARS-CoV-2 spike, S1 subunit, and nucleocapsid antigens were quantified using the ultra-sensitive Simoa® platform blinded for clinical features. SARS-CoV-2 specific humoral responses, including neutralizing antibodies, were also assessed.

RESULTS: At 6-12 months, SARS-CoV-2 antigenemia (any antigen) was detected in 31% of individuals with Long COVID, in 20% of those fully recovered and in 5.4% of uninfected controls. By 18-24 months, positivity declined to 3%, 0% and 0%, respectively. Full spike was the most frequent antigen detected, whereas S1 was rarely observed and nucleocapsid was absent in recovered participants. Antigenemia was not associated with number or type of persistent symptoms, antibody titers, including neutralizing capacity, or vaccination status.

CONCLUSION: SARS-CoV-2 antigens circulate in plasma up to one year after infection in a minority of individuals, regardless of whether they develop Long COVID or not, and become rarely detectable later on. Therefore, current evidence does not support its use to guide clinical monitoring or treatment decisions in Long COVID.