• Predictors of Nonseroconversion after SARS-CoV-2 Infection - Volume 27, Number 9—September 2021 - Emerging Infectious Diseases journal - CDC

    Nombre de personnes testées très faible, 72 au total.

    Not all persons recovering from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection develop SARS-CoV-2–specific antibodies. We show that nonseroconversion is associated with younger age and higher reverse transcription PCR cycle threshold values and identify SARS-CoV-2 viral loads in the nasopharynx as a major correlate of the systemic antibody response.



    In summary, we show that patients with low #SARS-CoV-2 viral loads in their respiratory tract are less likely to mount a systemic antibody response. Although we cannot formally exclude false-positive RT-PCR results in some participants, PCR contamination is highly unlikely as an explanation for our findings (Appendix). We also show that clinical illness does not guarantee seroconversion and that laboratories with highly sensitive RT-PCR assays are more likely to detect serologic nonresponders. These results provide an explanation for the puzzling variability of #seroconversion in different cohorts.

    The fact that a considerable fraction of RT-PCR positive persons fail to seroconvert has practical implications. Such persons remain undetected in seroprevalence studies, including in vaccine studies that assess protection from asymptomatic infection by measuring antibodies to antigens not included in the vaccine.

    Seroconverters and nonseroconverters will probably also respond differently to #vaccination. Recent studies revealed that seropositive persons have a heightened antibody response after the first, but not the second, dose of an mRNA vaccine, suggesting that a single dose is sufficient. Serologic nonresponders might not exhibit a similarly heightened anamnestic response, but resemble SARS-CoV-2 naive persons, as was observed for 1 previously infected vaccinee who never seroconverted (14). Finally, RT-PCR positive persons who experienced COVID-19 symptoms might be less inclined to seek vaccination, believing they are protected, but our results caution against this assumption.

    Comparing race/ethnicity, sex, and symptom severity, we failed to find a significant association with serostatus (Table), although we did observe a trend for increasing antibody positivity with increasing symptom severity (Appendix Figure 2). We also found no significant differences in seroconversion between patients reporting or not reporting various symptoms…

    #anticorps #immunité

    • Rappel :

      Covid-19 : pourquoi une infection par le SARS-CoV-2 n’est pas toujours synonyme d’un test sérologique positif

      ... théoriquement on peut imaginer que l’organisme parvienne à se débarrasser du coronavirus sans recourir aux anticorps ?

      SF-K : Oui, effectivement. Lorsque nous avons vérifié la réponse des lymphocytes T des partenaires qui avaient eu des symptômes mais étaient séronégatifs, on a constaté que chez plusieurs d’entre eux, elle était du même type que celle de leur partenaire « cas index ». Cela signifie qu’ils ont probablement été exposé au virus. Leur réponse T a peut-être été tellement efficace qu’elle a éliminé le virus, ou qu’ils n’ont eu besoin que de peu d’anticorps pour y parvenir, lesquels sont en quantité si faibles qu’ils n’ont pas pu être détectés ou ont disparu rapidement ensuite.

      Reste le cas des patients symptomatiques qui n’ont ni anticorps, ni réponse cellulaire T significative. Chez eux, on peut imaginer que la réponse immunitaire innée, immédiate, a suffi à éliminer le virus. Ils n’auraient donc pas eu besoin de déclencher le reste du processus.

  • Attack rates amongst household members of outpatients with confirmed #COVID-19 in Bergen, Norway : A case-ascertained study - ScienceDirect

    Attack rates = sujets asymptomatiques et symptomatiques

    Seuls les symptomatiques ont eu un PCR, mais tous ont eu une sérologie.

    La spécificité du test sérologique n’est pas discutée.

    #SARS-CoV-2 specific antibodies were measured in sera collected 6–8 weeks after index patient nasopharyngeal testing to define household attack rates.

    The overall attack rate was 45% (95% CI 38–53) assessed by serology, and 47% when also including seronegative RT-PCR positives. Serology identified a higher number of infected household members than RT-PCR [(44/70 vs. 32/70)],
    Attack rates were equally high in children (48%) and young adults (42%). The attack rates was 16% in asymptomatic household members [8/49] and 42% in RT-PCR negative contacts [16/38]. [...]

    Serological assays provide more sensitive and robust estimates of household attack rates than RT-PCR. Children are equally susceptible to infection as young adults . Negative RT-PCR or lack of symptoms are not sufficient to rule out infection in household members.

    #sérologie #séroconversion #asymptomatiques #enfants #transmission #anticorps

  • Kinetics of antibody responses dictate #COVID-19 outcome | medRxiv

    While high anti-S IgG levels correlated with worse disease severity, such correlation was time-dependent. Deceased patients did not have higher overall humoral response than live discharged patients. However, they mounted a robust, yet delayed response, measured by anti-S, anti-RBD IgG, and neutralizing antibody (NAb) levels, compared to survivors. Delayed #seroconversion kinetics correlated with impaired viral control in deceased patients. Finally, while sera from 89% of patients displayed some neutralization capacity during their disease course, NAb generation prior to 14 days of disease onset emerged as a key factor for recovery. These data indicate that COVID-19 mortality does not correlate with the cross-sectional antiviral antibody levels per se, but rather with the delayed kinetics of NAb production.

    #immunité #anticorps

  • Public health antibody screening indicates a six-fold higher #SARS-CoV-2 exposure rate than reported cases in children: Med

    • SARS-CoV-2 dual antibody strategy yielded 100% specificity and >95% sensitivity
    • Childhood surveillance finds 6-fold higher antibody prevalence than reported cases
    • Half of the antibody positive children were asymptomatic

    #anticorps #sérologie #séroconversion

  • Early Release - Antibody Responses to #SARS-CoV-2 at 8 Weeks Postinfection in Asymptomatic Patients - Volume 26, Number 10—October 2020 - Emerging Infectious Diseases journal - CDC

    We compared levels of severe acute respiratory syndrome coronavirus 2 neutralizing antibodies in recovery plasma from 7 completely asymptomatic coronavirus disease patients with those in symptomatic patients in South Korea. We found that serologic diagnostic testing was positive for 71% (5/7) of completely asymptomatic patients, but neutralizing antibody response occurred in all 7 patients.

    Neutralizing antibodies play an essential role in virus clearance and have been considered a critical immune player for protection against viral diseases. Knowledge of the neutralizing antibody response in asymptomatic patients is critical for diagnosing the disease, understanding pathogenesis, and interpreting seroepidemiologic data to define prevalence and risk factors for infection. Production of neutralizing antibodies in asymptomatic COVID-19 patients was reported recently. Wu et al. reported that ≈30% of recovered mild COVID-19 patients generated a deficient level of neutralizing antibody titers; in 10 of the 175 patients, the level was below the limit of detection (F. Wu et al., unpub. data, https://doi.org/10.1101/2020.03.30.20047365External Link). The difference in results from our study compared with the previous study might be caused by differences in the timing of the test. In the previous study, antibody tests were performed 2–3 weeks after symptom onset, whereas we tested 2 months after symptom onset or laboratory diagnosis. #Seroconversion in asymptomatic patients might take longer .

    #asymptomatique #asymptomatiques #anticorps #sérologie #immunité