Antibody correlates of protection from SARS-CoV-2 reinfection prior to vaccination: A nested case-control within the SIREN study.

OBJECTIVES: To investigate serological differences between SARS-CoV-2 reinfection cases and contemporary controls, to identify antibody correlates of protection against reinfection. METHODS: We performed a case-control study, comparing reinfection cases with singly infected individuals pre-vaccination, matched by gender, age, region and timing of first infection. Serum samples were tested for anti-SARS-CoV-2 spike (anti-S), anti-SARS-CoV-2 nucleocapsid (anti-N), live virus microneutralisation (LV-N) and pseudovirus microneutralisation (PV-N). Results were analysed using fixed effect linear regression and fitted into conditional logistic regression models. RESULTS: We identified 23 cases and 92 controls. First infections occurred before November 2020; reinfections occurred before February 2021, pre-vaccination. Anti-S levels, LV-N and PV-N titres were significantly lower among cases; no difference was found for anti-N levels. Increasing anti-S levels were associated with reduced risk of reinfection (OR 0·63, CI 0·47-0·85), but no association for anti-N levels (OR 0·88, CI 0·73-1·05). Titres >40 were correlated with protection against reinfection for LV-N Wuhan (OR 0·02, CI 0·001-0·31) and LV-N Alpha (OR 0·07, CI 0·009-0·62). For PV-N, titres >100 were associated with protection against Wuhan (OR 0·14, CI 0·03-0·64) and Alpha (0·06, CI 0·008-0·40). CONCLUSIONS: Before vaccination, protection against SARS-CoV-2 reinfection was directly correlated with anti-S levels, PV-N and LV-N titres, but not with anti-N levels. Detectable LV-N titres were sufficient for protection, whilst PV-N titres >100 were required for a protective effect. TRIAL REGISTRATION NUMBER: ISRCTN11041050.

A single drug-resistance mutation in HSV-1 UL52 primase points to a difference between two helicase-primase inhibitors in their mode of interaction with the antiviral target.

OBJECTIVES: To investigate the mechanism of action of the helicase-primase inhibitors (HPIs) BAY 57-1293 and BILS 22 BS by selection and characterization of drug-resistant herpes simplex virus (HSV)-1 mutants. METHODS: HSV-1 mutants were selected using BAY 57-1293 in Vero cells. Resistance mutations identified in the UL5 helicase or UL52 primase genes were validated by marker transfer. Cross-resistance to the structurally distinct BILS 22 BS was measured by ID(50) determinations. RESULTS: (i) A single mutation (UL52: A899T) confers 43-fold resistance to BAY 57-1293, but does not confer any resistance to BILS 22 BS. (ii) A double mutant (UL52: A899T and UL5: K356T) is 2500-fold resistant to BAY 57-1293, which is more than 17 times the sum of fold-resistance due to the individual mutations, UL52: A899T (43-fold) and UL5: K356T (100-fold). (iii) Virus containing the single helicase mutation and the double mutant with mutations in both helicase and primase showed equal resistance to BILS 22 BS (70-fold). CONCLUSIONS: By measuring the relative inhibitory concentrations required to overcome particular mutations in the helicase and primase proteins, evidence was obtained that BAY 57-1293 interacts with both components of the helicase-primase complex to achieve maximum potency, whereas for BILS 22BS, this may not be the case. Furthermore, our observations suggest that BAY 57-1293 interacts simultaneously with UL5 and UL52. Overall, the results suggest that these two potent HPIs interact differently with the helicase-primase complex.