Effect of booster vaccination against Delta and Omicron SARS-CoV-2 variants in Iceland

Insights on interferon-independent induction of interferon-stimulated genes shaping the lung's response in early SARS-CoV-2 infection

While mRNA vaccine efficacy against the 2019 coronavirus disease (COVID-19) outbreak remains high, research on antiviral innate immune responses in the early stages of infection is essential to develop strategies to prevent the dissemination of SARS-CoV-2. In this study, we investigated the induction of both interferon (IFN)-stimulated genes (ISGs) and IFN-independently upregulated ISGs following SARS-CoV-2 infection in Syrian golden hamsters. The viral titers were highest at 3 days post-infection (dpi). Over time, the viral titer gradually decreased while ISGs such as Mx1, Ifit2, Ifit3, Ifi44, and Rsad2 were markedly induced in the lung. The transcription of ISGs significantly increased from 2 dpi, and SARS-CoV-2-induced ISGs were maintained in the hamster lung until 7 dpi. The transcription of Ifnb and Ifng was minimally elevated, while Ifnl2/3 was significantly induced in the lung at 5 days after SARS-CoV-2 infection. RNA sequencing results also showed that at 3 dpi, SARS-CoV-2 initiated the activation of ISGs, with lesser increases of Ifnl2 and Ifnl3 transcription. In addition, Ddx58 and cGAS, which encode factors for virus sensing, Stat1, Stat2, and IFN regulatory factor 7 and 9 mRNA levels were also induced at the initial stage of infection. Our data demonstrate that ISGs might be upregulated in the lung in response to SARS-CoV-2 during the early stages of infection, and the rapid induction of ISGs was not associated with the activation of IFNs. Elucidation of IFN-independent induction of ISGs could further our understanding of alternative defense mechanisms employed by the lungs against SARS-CoV-2 and provide more effective antiviral strategies for patients with severe COVID-19.

Comparing COVID-19 pandemic health responses in two high-income island nations: Iceland and New Zealand

AIMS

We aimed to compare COVID-19 control measures, epidemiological characteristics and economic performance measures in two high-income island nations with small populations, favorable border control options, and relatively good outcomes: Iceland and New Zealand (NZ).

METHODS

We examined peer-reviewed journal articles, official websites, reports, media releases and press articles for data on pandemic preparedness and COVID-19 public health responses from 1 January 2020 to 1 June 2022 in Iceland and NZ. We calculated epidemiological characteristics of the COVID-19 pandemic, as well as measures of economic performance.

RESULTS

Both nations had the lowest excess mortality in the OECD from the start of the pandemic up to June 2022. Iceland pursued a mitigation strategy, never used lockdowns or officially closed its border to foreign nationals, and instead relied on extensive testing and contact tracing early in the pandemic. Meanwhile, NZ pursued an elimination strategy, used a strict national lockdown to stop transmission, and closed its international border to everyone except citizens and permanent residents going through quarantine and testing. Iceland experienced a larger decrease in gross domestic product in 2020 (relative to 2019) than NZ (-8·27% vs. -1·22%, respectively). In late 2021, NZ announced a shift to a suppression strategy and in 2022 began to reopen its border in stages, while Iceland ended all public restrictions on 25 February 2022.

CONCLUSIONS

Many of Iceland's and NZ's pandemic control measures appeared successful and features of the responses in both countries could potentially be adopted by other jurisdictions to address future disease outbreaks and pandemic threats.

Effectiveness of mRNA Booster Vaccination Against Mild, Moderate, and Severe COVID-19 Caused by the Omicron Variant in a Large, Population-Based, Norwegian Cohort

BACKGROUND

Understanding how booster vaccination can prevent moderate and severe illness without hospitalization is crucial to evaluate the full advantage of mRNA boosters.

METHODS

We followed 85 801 participants (aged 31-81 years) in 2 large population-based cohorts during the Omicron BA.1/2 wave. Information on home testing, PCR testing, and symptoms of coronavirus disease 2019 (COVID-19) was extracted from biweekly questionnaires covering the period 12 January 2022 to 7 April 2022. Vaccination status and data on previous SARS-CoV-2 infection were obtained from national registries. Cox regression was used to estimate the effectiveness of booster vaccination compared to receipt of 2-dose primary series >130 days previously.

RESULTS

The effectiveness of booster vaccination increased with increasing severity of COVID-19 and decreased with time since booster vaccination. The effectiveness against severe COVID-19 was reduced from 80.9% shortly after booster vaccination to 63.4% in the period >90 days after vaccination. There was hardly any effect against mild COVID-19. The effectiveness tended to be lower among subjects aged ≥60 years than those aged <50 years.

CONCLUSIONS

This is the first population-based study to evaluate booster effectiveness against self-reported mild, moderate, and severe COVID-19. Our findings contribute valuable information on duration of protection and thus timing of additional booster vaccinations.