At least 5–10% of subjects surviving COVID-19 develop the post-COVID-19 condition (PCC) or “Long COVID”. The clinical presentation of PCC is heterogeneous, its pathogenesis is being deciphered, and objective, validated biomarkers are lacking. It is unknown if PCC is a single entity or a heterogeneous syndrome with overlapping pathophysiological basis. The large US RECOVER study identified four clusters of subjects with PCC according to their presenting symptoms. However, the long-term clinical implications of PCC remain unknown. We conducted a 2-year prospective cohort study of subjects surviving COVID-19, including individuals fulfilling the WHO PCC definition and subjects with full clinical recovery. We systematically collected post-COVID-19 symptoms using prespecified questionnaires and performed additional diagnostic imaging tests when needed. Factors associated with PCC were identified and modelled using logistic regression. Unsupervised clustering analysis was used to group subjects with PCC according to their presenting symptoms. Factors associated with PCC recovery were modelled using a direct acyclic graph approach. The study included 548 individuals, 341 with PCC, followed for a median of 23 months (IQR 16.5–23.5), and 207 subjects fully recovered. In the model with the best fit, subjects who were male and had tertiary studies were less likely to develop PCC, whereas a history of headache, or presence of tachycardia, fatigue, neurocognitive and neurosensitive complaints and dyspnea at COVID-19 diagnosis predicted the development of PCC. The cluster analysis revealed the presence of three symptom clusters with an additive number of symptoms. Only 26 subjects (7.6%) recovered from PCC during follow-up; almost all of them (n = 24) belonged to the less symptomatic cluster A, dominated mainly by fatigue. Recovery from PCC was more likely in subjects who were male, required ICU admission, or had cardiovascular comorbidities, hyporexia and/or smell/taste alterations during acute COVID-19. Subjects presenting with muscle pain, impaired attention, dyspnea, or tachycardia, conversely, were less likely to recover from PCC. Preexisting medical and socioeconomic factors, as well as acute COVID-19 symptoms, are associated with the development of and recovery from the PCC. Recovery is extremely rare during the first 2 years, posing a major challenge to healthcare systems. Fundació Lluita contra les Infeccions.

Background: SARS-CoV-2 vaccination is the most effective strategy to protect older residents of long-term care facilities (LTCF) against severe COVID-19, but primary vaccine responses are less effective in older adults. Here, we characterised the humoral responses of institutionalised seniors 3 months after they had received the mRNA/BNT162b2 vaccine. Methods: plasma levels of SARS-CoV-2-specific total IgG, IgM and IgA antibodies were measured before and 3 months after vaccination in older residents of LTCF. Neutralisation capacity was assessed in a pseudovirus neutralisation assay against the original WH1 and later B.1.617.2/Delta variants. A group of younger adults was used as a reference group. Results: three months after vaccination, uninfected older adults presented reduced SARS-CoV-2-specific IgG levels and a significantly lower neutralisation capacity against the WH1 and Delta variants compared with vaccinated uninfected younger individuals. In contrast, COVID-19-recovered older adults showed significantly higher SARS-CoV-2-specific IgG levels after vaccination than their younger counterparts, whereas showing similar neutralisation activity against the WH1 virus and an increased neutralisation capacity against the Delta variant. Although, similarly to younger individuals, previously infected older adults elicit potent cross-reactive immune responses, higher quantities of SARS-CoV-2-specific IgG antibodies are required to reach the same neutralisation levels. Conclusions: although hybrid immunity seems to be active in previously infected older adults 3 months after mRNA/BNT162b2 vaccination, humoral immune responses are diminished in COVID-19 uninfected but vaccinated older residents of LTCF. These results suggest that a vaccine booster dose should be prioritised for this particularly vulnerable population.

This is an observational, cross-sectional, comparative case–control, pilot study aimed at assessing the impact of HIV infection and age on immunological markers in people with HIV (PWH) on antiretroviral therapy (ART). The study included 40 PWH on ART, divided into two age groups (40–45 years vs. ≥60 years), and 30 HIV-uninfected controls matched by sex and age. The results show that older PWH on ART had more comorbidities and a higher frequency of CD8 T cells compared to older controls, with a significant decrease in CD8 naïve T cells with age. Additionally, younger PWH on ART exhibited higher frequencies of activated CD8 T cells and elevated levels of inflammatory markers (sCD14, IL-6) compared to age-matched controls, with values similar to those of older PWH on ART. These findings suggest that younger PWH on ART may experience accelerated immunoaging, highlighting the need for early interventions in this population.

The biological mechanisms underlying long COVID in the pediatric population are poorly understood. Our study aimed to characterize the immune pathophysiology of long COVID in this population. We analyzed major immune cell compartments in PBMCs and the specific SARS-CoV-2 antibody response in 99 patients with long COVID and in 18 patients without long COVID at 3 months after acute infection. Our findings indicate that pediatric long COVID is associated with a dysregulated immune response characterized by altered innate immunity and overactivated T, B, and NK cell responses. Furthermore, young people with long COVID had an impaired humoral response to SARS-CoV-2 marked by a dysregulated B cell compartment and lower levels of anti-RBD IgG and IgA. This correlated with reduced neutralizing capacity against SARS-CoV-2. Random forest analysis identified CCR6 expression on myeloid cells as the most relevant biomarker that distinguishes individuals with long COVID from control individuals with 79% accuracy.

Although SARS-CoV-2 reinfections remain a concern for healthcare systems worldwide, the factors driving them are still not fully understood. In this study, we examined data for 3303 individuals who experienced two SARS-CoV-2 infections between March 2020 and May 2022 from both clinical and viral genomics perspectives. Our findings indicate that viral evolution was the primary driver of reinfection. However, chronic conditions were common among reinfected individuals, including those under 26 years old, suggesting that the presence of underlying and/or chronic conditions increases susceptibility to reinfection. The median time elapsed between infections was one year, often coinciding with the emergence of new variants. While vaccination showed only a limited protective effect against reinfection, it drastically decreased the hospitalization rate, underscoring its role in mitigating disease severity. Our findings point to the need for more flexible vaccination strategies, especially for individuals with chronic conditions. Understanding the interactions between host factors and viral evolution is critical to strengthening prevention strategies and reducing the burden of reinfections and their possible long-term complications.

Background: Long COVID (LC) is characterized by persistent and, often, disabling symptoms, yet its biological basis remains unclear. Multiple mechanisms, including immune dysregulation, endothelial dysfunction, and viral persistence, have been proposed, although it is unknown whether these define distinct biological subtypes or overlapping processes.Methods: We conducted a cross-sectional analysis of 314 unvaccinated individuals, including 141 people with long COVID (PWLC), 99 COVID-19-recovered controls (both groups sampled a median of 8 months after primary SARS-CoV-2 infection), and 74 uninfected participants. Circulating immune and endothelial biomarkers were quantified, and viral persistence was assessed by plasma SARS-CoV-2 RNA detection. Herpesviruses reactivation and SARS-CoV-2 humoral responses were also evaluated. Associations with symptom persistence were analyzed using multivariable models and machine learning approaches.Findings: Most soluble biomarker differences primarily distinguished previously infected individuals from uninfected controls rather than PWLC from recovered participants. Increased IL-1 receptor antagonist (IL-1RA) levels, together with reduced IL-1β/IL-1RA ratios, were the immune alterations most strongly associated with LC, while P-selectin was the endothelial marker most consistently linked to symptom persistence. Global biomarker profiles overlapped across groups and showed limited classification performance. Plasma SARS-CoV-2 RNA was detected in a minority of participants in both PWLC and recovered individuals, although PWLC showed lower Ct values and viral RNA was repeatedly associated with persistent symptoms. Epstein-Barr virus reactivation signatures were increased in PWLC, whereas SARS-CoV-2-specific antibody levels were comparable between groups.Interpretation: LC may arise from overlapping immune, endothelial, and viral perturbations rather than discrete biomarker-defined subtypes.