BackgroundThe duration of immune response to COVID-19 vaccination is of major interest. Our aim was to analyze the determinants of anti-SARS-CoV-2 IgG titer at 6 months after 2-dose vaccination in an international cohort of vaccinated healthcare workers (HCWs).MethodsWe analyzed data on levels of anti-SARS-CoV-2 Spike antibodies and sociodemographic and clinical characteristics of 6,327 vaccinated HCWs from 8 centers from Germany, Italy, Romania and Slovakia. Time between 1st dose and serology ranged 150-210 days. Serological levels were log-transformed to account for the skewness of the distribution and normalized by dividing them by center-specific standard errors, obtaining standardized values. We fitted center-specific multivariate regression models to estimate the cohort-specific relative risks (RR) of an increase of 1 standard deviation of log antibody level and corresponding 95% confidence interval (CI), and finally combined them in random-effects meta-analyses.ResultsA 6-month serological response was detected in 99.6% of HCWs. Female sex (RR 1.10, 95%CI 1.00-1.21), past infection (RR 2.26, 95%CI 1.73-2.95) and two vaccine doses (RR 1.50, 95%CI 1.22-1.84) predicted higher IgG titer, contrary to interval since last dose (RR for 10-day increase 0.94, 95%CI 0.91-0.97) and age (RR for 10-year increase 0.87, 95%CI 0.83-0.92). M-RNA-based vaccines (p<0.001) and heterologous vaccination (RR 2.46, 95%CI 1.87-3.24, one cohort) were associated with increased antibody levels.ConclusionsFemale gender, young age, past infection, two vaccine doses, and m-RNA and heterologous vaccination predicted higher antibody level at 6 months. These results corroborate previous findings and offer valuable data for comparison with trends observed with longer follow-ups.

Background: The research aimed to investigate the incidence of SARS-CoV-2 breakthrough infections and their determinants in a large European cohort of more than 60,000 health workers. Methods: A multicentric retrospective cohort study, involving 12 European centers, was carried out within the ORCHESTRA project, collecting data up to 18 November 2021 on fully vaccinated health workers. The cumulative incidence of SARS-CoV-2 breakthrough infections was investigated with its association with occupational and social–demographic characteristics (age, sex, job title, previous SARS-CoV-2 infection, antibody titer levels, and time from the vaccination course completion). Results: Among 64,172 health workers from 12 European health centers, 797 breakthrough infections were observed (cumulative incidence of 1.2%). The primary analysis using individual data on 8 out of 12 centers showed that age and previous infection significantly modified breakthrough infection rates. In the meta-analysis of aggregated data from all centers, previous SARS-CoV-2 infection and the standardized antibody titer were inversely related to the risk of breakthrough infection (p = 0.008 and p = 0.007, respectively). Conclusion: The inverse correlation of antibody titer with the risk of breakthrough infection supports the evidence that vaccination plays a primary role in infection prevention, especially in health workers. Cellular immunity, previous clinical conditions, and vaccination timing should be further investigated.

This paper examines external debt and economic growth relationship in a panel of 48 Sub-Saharan Africa countries (SSA) for the period 1990-2017 using a two-step system General Method of Moments (GMM) technique. Our study shows that contemporaneously, external debt has a negative and statistically significant impact on GDP growth. However, the first lag of external debt variables stimulates GDP growth. The implication is that external debt accumulated in the previous period makes funds available for growth enhancing expenditure in the next period. Furthermore, our study found no evidence of a non-linear relationship between debt and economic growth. Lastly, we found that the deleterious impact of external debt on GDP growth does not preclude poor or rich SSA countries. We recommend the adoption of state-of-the-art measures in collecting domestic revenue to complement external revenue sources. In addition, we advocate for strong macroeconomic environment in SSA so that yield negotiation on the debt will not dissipate the coffers of SSA countries via high debt servicing cost. Contribution/Originality: This study uses new estimation methodology to unravel the external debt and economic growth nexus in Sub-Saharan Africa countries. 1. INTRODUCTION Sustainable economic growth and development is the main concern for all economies worldwide , especially Sub-Saharan Africa (SSA) 1 countries that happen to find themselves at the lower end of the growth chart. The quest to achieve these goals of economic growth and sustainable development calls for huge outlays which invariably comes from external sources with high servicing cost which perhaps, has plunged SSA into an uncomfortable fiscal position. Researchers like (Eaton, 1993) argues that external debt complements domestic savings and investment, hence it enhances growth. Of different opinion is Krugman (1988) who posits that debt servicing causes disruptions in an economy, hence it discourages investment and economic growth. The impact of the global economic downturn in the mid-1980s on developing economies, including the debt crisis, was such that the 1980s is often referred to as the lost decade for Africa (Iyoha, 1999). The debt burden on SSA after the lost decade has stagnated many of its economies which led to the adoption of SAPS 2 aimed at reducing the SSA fiscal imbalances. However, the pace of 1 According to the United Nations, Sub-Saharan Africa countries are all African countries who are fully or partially located south of the Sahara.

Background: The persistence of antibody levels after COVID-19 vaccination has public health relevance. We analyzed the determinants of quantitative serology at 9 months after vaccination in a multicenter cohort. Methods: We analyzed data on anti-SARS-CoV-2 spike antibody levels at 9 months from the first dose of vaccinated HCW from eight centers in Italy, Germany, Spain, Romania and Slovakia. Serological levels were log-transformed to account for the skewness of the distribution and normalized by dividing them by center-specific standard errors. We fitted center-specific multivariate regression models to estimate the cohort-specific relative risks (RR) of an increase of one standard deviation of log antibody level and the corresponding 95% confidence interval (CI), and combined them in random-effects meta-analyses. Finally, we conducted a trend analysis of 1 to 7 months’ serology within one cohort. Results: We included 20,216 HCW with up to two vaccine doses and showed that high antibody levels were associated with female sex (p = 0.01), age (RR = 0.87, 95% CI = 0.86–0.88 per 10-year increase), 10-day increase in time since last vaccine (RR = 0.97, 95% CI 0.97–0.98), previous infection (3.03, 95% CI = 2.92–3.13), two vaccine doses (RR = 1.22, 95% CI = 1.09–1.36), use of Spikevax (OR = 1.51, 95% CI = 1.39–1.64), Vaxzevria (OR = 0.57, 95% CI = 0.44–0.73) or heterologous vaccination (OR = 1.33, 95% CI = 1.12–1.57), compared to Comirnaty. The trend in the Bologna cohort, based on 3979 measurements, showed a decrease in mean standardized antibody level from 8.17 to 7.06 (1–7 months, p for trend 0.005). Conclusions: Our findings corroborate current knowledge on the determinants of COVID-19 vaccine-induced immunity and declining trend with time.

This study employs threshold models to examine the export-led growth hypothesis (ELG) for Ghana from 1970-2018. The analysis commences as follows. Firstly, using real GDP as threshold variable, the study conducts a non-linearity test for the threshold vector autoregressive (TVAR) model as against the linear vector autoregressive (VAR) model. Secondly, the study evaluates whether the ELG hypothesis is best explained with linear co-integration models or threshold cointegration models. The empirical results indicate that, the ELG hypothesis is supported by the two-threshold vector autoregressive model (threshold values of 2.35 and 2.46) and a two-threshold vector error correction model (threshold values -0.50 and -0.20). The error correction term of the TVECM is negative and statistically different from zero, signifying speed of long run convergence. In terms of threshold cointegration, real GDP versus real exports and real GDP vs real imports are threshold co-integrated. In contrast, the null hypothesis of linear co-integration is not rejected for real export versus real import. Contribution/Originality:This study uses new estimation methodology to evaluate the export -output growth nexus for Ghana for the period spanning from 1970-2018. INTRODUCTIONAccording to Ulrich (2014); Krueger (1978); Ram (1985); Salvatore and Hatcher (1991) export-output hypothesis (ELG) is described as the positive effects of export growth on output through its multiplier effect. The unanimous argument gravitates towards the believe that exports stimulates output growth (see for instance Rivera-Batiz and Romer (1991)). Alternatively, Arnade and Vasavada (1995); Ghartey (1993); Lancaster (1980); Stavrinos (1987) argued in favour of the growth-led exports (GLE) hypothesis, that is output growth causes export growth.Hitherto, the literature on ELG has documented some findings and they are categorised as follows. The earlier studies such as Balassa (1978); Michaely (1977); Heller and Porter (1978);Tyler (1981);Feder (1983) focused on cross-country analysis. They found that exports positively affect output growth in developing countries. However, their study precluded the plausibility of causality running from exports to imports or vice versa. Another group of studies evaluated the export-output nexus for individual countries using (Granger, 1969) or Sims (1972) causality test. Findings showed exports growth has no causal impact on output growth (see for instance (Dodaro