Highlights d Antibodies to four COVID-19 vaccines differed in an observational study in Mongolia d Responses from high to low: Pfizer/BioNTech > AstraZeneca > Sputnik V > Sinopharm d Breakthrough infections in June to early July of 2021 were due mostly to the Alpha variant d After breakthrough infection, high antibody levels are seen in all vaccine groups

Hepatitis delta virus (HDV) is a satellite RNA virus that requires the presence of hepatitis B virus (HBV) for its replication. HDV/HBV co‐infection is often associated with a faster disease progression of chronic hepatitis in comparison to HBV mono‐infection. Therefore, the development of novel antiviral therapies targeting HDV represents a high priority and an urgent medical need. In this review, we summarize the ongoing efforts to evaluate promising HDV‐specific drugs, such as lonafarnib (LNF), pegylated interferon lambda (PEG‐IFN‐λ) and their use as a combination therapy. Furthermore, we review the most recent developments in the area of anti‐HBV drugs with potential effects against HDV, including therapeutic agents targeting hepatitis B surface antigen (HBsAg) expression, secretion and function. Finally, we consider the important insights that have emerged from the development of these potential antiviral strategies, as well as the intriguing questions that remain to be elucidated in this rapidly changing field.

Different vaccines for SARS-CoV-2 are approved in various countries, but few direct comparisons of the antibody responses they stimulate have been reported. We collected plasma specimens in July 2021 from 196 Mongolian participants fully vaccinated with one of four Covid vaccines: Pfizer/BioNTech, AstraZeneca, Sputnik V and Sinopharm. Functional antibody testing with a panel of nine SARS-CoV-2 viral variant RBD proteins reveal marked differences in the vaccine responses, with low antibody levels and RBD-ACE2 blocking activity stimulated by the Sinopharm and Sputnik V vaccines in comparison to the AstraZeneca or Pfizer/BioNTech vaccines. The Alpha variant caused 97% of infections in Mongolia in June and early July 2021. Individuals who recover from SARS-CoV-2 infection after vaccination achieve high antibody titers in most cases. These data suggest that public health interventions such as vaccine boosting, potentially with more potent vaccine types, may be needed to control the COVID-19 pandemic in Mongolia and worldwide.

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