tetano
Editor, Senior Moderator
J Biomed Sci
. 2026 Jul 22;33(1):77.
doi: 10.1186/s12929-026-01276-5.
Hidden asymptomatic breakthrough infection in a proof-of-concept longitudinal study on SARS-CoV-2 vaccine recipients
Chiaho Shih[SUP] 1 2 [/SUP], You-Zhen Liao[SUP] #[/SUP][SUP] 3 [/SUP], Che-Yu Hsu[SUP] #[/SUP][SUP] 3 [/SUP], Ying-Chen Tsai[SUP] #[/SUP][SUP] 3 [/SUP], Ming-Yen Lin[SUP] #[/SUP][SUP] 4 5 [/SUP], Hsin-Ying Clair Chiou[SUP] 6 7 [/SUP], Wen-Hui Kuan[SUP] 3 [/SUP], Chih-Hsu Chang[SUP] 8 [/SUP], An-Ting Liou[SUP] 3 [/SUP], Yu-Chi Chou[SUP] 9 [/SUP], Jih-Jin Tsai[SUP] 10 11 12 [/SUP], Ping-Chang Lin[SUP] 10 [/SUP], Ming-Lung Yu[SUP] 13 [/SUP], Wan-Long Chuang[SUP] 13 [/SUP], Jia-Jung Lee[SUP] 4 12 [/SUP], Jer-Ming Chang[SUP] 4 12 [/SUP], Shang-Jyh Hwang[SUP] 4 12 14 [/SUP], Justin Shih[SUP] 15 [/SUP], Wen-Chun Hung[SUP] 16 [/SUP], Ming-Feng Hou[SUP] 17 [/SUP], Inn-Wen Chong[SUP] 18 19 [/SUP], Yuh-Jyh Jong[SUP] 20 [/SUP], Jung-San Chang[SUP] 21 22 [/SUP]
Affiliations
Background: Individuals with asymptomatic SARS-CoV-2 infection can unknowingly transmit the virus, yet identifying such subclinical infections in post-vaccinated populations remains challenging.
Methods: We conducted a longitudinal study of 129 infection-naïve vaccine recipients immunized with various combinations of SARS-CoV-2 spike (S) protein vaccine platforms. Sera were collected before the first dose (v1), at 2 weeks (v7) and 6 months (v8) after the third dose. Taiwan's first major COVID-19 outbreak occurred between v7 and v8. We measured anti-nucleocapsid (anti-N) and anti-S IgG antibody titers by ELISA and assessed virus-neutralizing activity using live virus and pseudovirus assays.
Results: By developing an iterative serial screening method, we identified asymptomatic breakthrough (post-vaccination) infections among unconfirmed cases. Our v7-v8 paired cohort resolved into three distinct groups: confirmed cases (21%), asymptomatic breakthrough infections (17%), and uninfected subjects (62%). In normalized v8 sera, confirmed cases exhibited an anti-S[SUP]+++[/SUP] (high) /anti-N[SUP]+++[/SUP] (high) phenotype, while uninfected subjects showed an anti-S[SUP]+[/SUP] (low)/anti-N[SUP]+[/SUP](baseline) phenotype. Statistical analysis validated a distinct asymptomatic group characterized by an antibody profile anti-S[SUP]++[/SUP] (intermediate) /anti-N[SUP]+[/SUP] (baseline).
Conclusions: This approach may enable more accurate estimates of vaccine efficacy and infection prevalence. In a spike-vaccinated population, anti-N antibody is more a potential specific marker for COVID-19 symptomatic disease than an ideal marker for SARS-CoV-2 infection. To our knowledge, this is the first preliminary report of identification of asymptomatic breakthrough infection from a well-vaccinated population using self-matched longitudinal pairs of serum samples.
Keywords: Anti-nucleocapsid (N) antibody; Anti-spike (S) neutralizing antibody (nAb); Asymptomatic breakthrough infection; COVID-19; SARS-CoV-2; Vaccine.
. 2026 Jul 22;33(1):77.
doi: 10.1186/s12929-026-01276-5.
Hidden asymptomatic breakthrough infection in a proof-of-concept longitudinal study on SARS-CoV-2 vaccine recipients
Chiaho Shih[SUP] 1 2 [/SUP], You-Zhen Liao[SUP] #[/SUP][SUP] 3 [/SUP], Che-Yu Hsu[SUP] #[/SUP][SUP] 3 [/SUP], Ying-Chen Tsai[SUP] #[/SUP][SUP] 3 [/SUP], Ming-Yen Lin[SUP] #[/SUP][SUP] 4 5 [/SUP], Hsin-Ying Clair Chiou[SUP] 6 7 [/SUP], Wen-Hui Kuan[SUP] 3 [/SUP], Chih-Hsu Chang[SUP] 8 [/SUP], An-Ting Liou[SUP] 3 [/SUP], Yu-Chi Chou[SUP] 9 [/SUP], Jih-Jin Tsai[SUP] 10 11 12 [/SUP], Ping-Chang Lin[SUP] 10 [/SUP], Ming-Lung Yu[SUP] 13 [/SUP], Wan-Long Chuang[SUP] 13 [/SUP], Jia-Jung Lee[SUP] 4 12 [/SUP], Jer-Ming Chang[SUP] 4 12 [/SUP], Shang-Jyh Hwang[SUP] 4 12 14 [/SUP], Justin Shih[SUP] 15 [/SUP], Wen-Chun Hung[SUP] 16 [/SUP], Ming-Feng Hou[SUP] 17 [/SUP], Inn-Wen Chong[SUP] 18 19 [/SUP], Yuh-Jyh Jong[SUP] 20 [/SUP], Jung-San Chang[SUP] 21 22 [/SUP]
Affiliations
- PMID: 42487117
- PMCID: PMC13393500
- DOI: 10.1186/s12929-026-01276-5
Background: Individuals with asymptomatic SARS-CoV-2 infection can unknowingly transmit the virus, yet identifying such subclinical infections in post-vaccinated populations remains challenging.
Methods: We conducted a longitudinal study of 129 infection-naïve vaccine recipients immunized with various combinations of SARS-CoV-2 spike (S) protein vaccine platforms. Sera were collected before the first dose (v1), at 2 weeks (v7) and 6 months (v8) after the third dose. Taiwan's first major COVID-19 outbreak occurred between v7 and v8. We measured anti-nucleocapsid (anti-N) and anti-S IgG antibody titers by ELISA and assessed virus-neutralizing activity using live virus and pseudovirus assays.
Results: By developing an iterative serial screening method, we identified asymptomatic breakthrough (post-vaccination) infections among unconfirmed cases. Our v7-v8 paired cohort resolved into three distinct groups: confirmed cases (21%), asymptomatic breakthrough infections (17%), and uninfected subjects (62%). In normalized v8 sera, confirmed cases exhibited an anti-S[SUP]+++[/SUP] (high) /anti-N[SUP]+++[/SUP] (high) phenotype, while uninfected subjects showed an anti-S[SUP]+[/SUP] (low)/anti-N[SUP]+[/SUP](baseline) phenotype. Statistical analysis validated a distinct asymptomatic group characterized by an antibody profile anti-S[SUP]++[/SUP] (intermediate) /anti-N[SUP]+[/SUP] (baseline).
Conclusions: This approach may enable more accurate estimates of vaccine efficacy and infection prevalence. In a spike-vaccinated population, anti-N antibody is more a potential specific marker for COVID-19 symptomatic disease than an ideal marker for SARS-CoV-2 infection. To our knowledge, this is the first preliminary report of identification of asymptomatic breakthrough infection from a well-vaccinated population using self-matched longitudinal pairs of serum samples.
Keywords: Anti-nucleocapsid (N) antibody; Anti-spike (S) neutralizing antibody (nAb); Asymptomatic breakthrough infection; COVID-19; SARS-CoV-2; Vaccine.