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Introduction: Repeated COVID-19 booster vaccination was recommended in healthcare workers (HCWs) to maintain protection. We measured the relative vaccine effectiveness (rVE) of the second booster dose of COVID-19 vaccine compared to the first booster, against laboratory-confirmed SARS-CoV-2 infection in HCWs. Methods: In a prospective cohort study among HCWs from 12 European hospitals, we collected nasopharyngeal or saliva samples at enrolment and during weekly/fortnightly follow-up between October 2022 and May 2023. We estimated rVE of the second versus first COVID-19 vaccine booster dose against SARS-CoV-2 infection, overall, by time since second booster and restricted to the bivalent vaccines only. Using Cox regression, we calculated the rVE as (1-hazard ratio)*100, adjusting for hospital, age, sex, prior SARS-CoV-2 infection and at least one underlying condition. Results: Among the 979 included HCWs eligible for a second booster vaccination, 392 (40 %) received it and 192 (20 %) presented an infection during the study period. The rVE of the second versus first booster dose was −5 % (95 %CI: −46; 25) overall, 3 % (−46; 36) in the 7–89 days after receiving the second booster dose. The rVE was 11 % (−43; 45) when restricted to the use of bivalent vaccines only. Conclusion: The bivalent COVID-19 could have reduced the risk of SARS-CoV-2 infection among HCWs by 11 %. However, we note the limitation of imprecise rVE estimates due to the proportion of monovalent vaccine used in the study, the small sample size and the study being conducted during the predominant circulation of XBB.1.5 sub-lineage. COVID-19 vaccine effectiveness studies in HCWs can provide important evidence to inform the optimal timing and the use of updated COVID-19 vaccines.

Primary Breast Lymphoma: Clinical and Morphological Characteristics Introduction. Primary breast lymphoma constitutes only 0.004 - 0.5% of malignant breast tumours. The correct diagnostics of this rare neoplasm necessitates routine application of evidence-based diagnostic methods including immunohistochemistry (IHC). The aim of the study was to detect the frequency of primary breast lymphoma among consecutive well-characterised breast tumours in Latvian patients and to provide the essential clinical, radiological and morphological characteristics. Materials and Methods included review of the morphological data and routine IHC as well as clinical, laboratory and radiological findings in 474 consecutive patients diagnosed with malignant breast tumours. Results: The frequency of primary breast lymphoma was 0.63% [95% confidence interval = 0.22 - 1.84%]. All cases were represented by diffuse large B-cell lymphoma. Rapid progression, unilateral localisation and no evidence of extra-mammary spread was characteristic. Occurrence in a male patient was also observed. Conclusions: Breast lymphoma occurs in the local population with the incidence 0.63% of malignant breast tumours. The lesion retains significance for practising surgeon due to diagnostic pathway and occasional application of surgical treatment. Diffuse large B-cell lymphoma is the most frequent type of breast lymphoma. Immunohistochemical investigation is mandatory to identify breast lymphoma and perform reliable differential diagnosis with other high-grade malignant tumours. [PUBLICATION ABSTRACT]