Primary and booster vaccination in reducing severe clinical outcomes associated with Omicron Naïve infection

COVID-19 Vaccine Effectiveness of Booster Doses Against Delta and Omicron Variants Over Follow-up Times Using Longitudinal Meta-analysis

BACKGROUND

COVID-19 is a viral disease caused by the SARS-CoV-2, leading to several variants. This study aimed to examine the effectiveness of booster doses against the Delta and Omicron variants over different follow-up times. Study Design: This was a longitudinal meta-analysis.

METHODS

Searches were performed in PubMed, Cochrane Library, Scopus, and Web of Science databases, and eighty studies were selected for investigation. The analyses were separately performed on the unvaccinated control group (UNVCG) and the complete two doses of the vaccine control group (C2DCG) against Delta and Omicron variants. Three outcomes were examined, including symptomatic infection, hospitalization, and death.

RESULTS

Vaccine effectiveness (VE) in UNVCG studies for symptomatic infection revealed a non-linear trend against Omicron with a peak of 67.3%, declining to 27.1% after 25 weeks after a booster dose. The mean of VE for hospitalization over time started to decrease after four weeks against Omicron and after eight weeks against Delta. The VE reached a peak at week eight (96.0%) and started to decline with a VE of 93.3% after 20 weeks after the booster dose against Delta. It was 90.8% at week four and decreased to 73.4% after 25 weeks after the booster dose against Omicron. VE in the C2DCG studies demonstrated more decreases in outcomes over time.

CONCLUSION

Our findings showed a tendency to decrease effectiveness over time based on outcomes and variants. The early protection levels were lower in Omicron. Moreover, the VE decrease over time was stronger in Omicron compared to the Delta variant.

Kinetics of Viral Shedding for Outbreak Surveillance of Emerging Infectious Diseases: Modeling Approach to SARS-CoV-2 Alpha and Omicron Infection

BACKGROUND

Previous studies have highlighted the importance of viral shedding using cycle threshold (Ct) values obtained via reverse transcription polymerase chain reaction to understand the epidemic trajectories of SARS-CoV-2 infections. However, it is rare to elucidate the transition kinetics of Ct values from the asymptomatic or presymptomatic phase to the symptomatic phase before recovery using individual repeated Ct values.

OBJECTIVE

This study proposes a novel Ct-enshrined compartment model to provide a series of quantitative measures for delineating the full trajectories of the dynamics of viral load from infection until recovery.

METHODS

This Ct-enshrined compartment model was constructed by leveraging Ct-classified states within and between presymptomatic and symptomatic compartments before recovery or death among people with infections. A series of recovery indices were developed to assess the net kinetic movement of Ct-up toward and Ct-down off recovery. The model was applied to (1) a small-scale community-acquired Alpha variant outbreak under the "zero-COVID-19" policy without vaccines in May 2021 and (2) a large-scale community-acquired Omicron variant outbreak with high booster vaccination rates following the lifting of the "zero-COVID-19" policy in April 2022 in Taiwan. The model used Bayesian Markov chain Monte Carlo methods with the Metropolis-Hastings algorithm for parameter estimation. Sensitivity analyses were conducted by varying Ct cutoff values to assess the robustness of the model.

RESULTS

The kinetic indicators revealed a marked difference in viral shedding dynamics between the Alpha and Omicron variants. The Alpha variant exhibited slower viral shedding and lower recovery rates, but the Omicron variant demonstrated swifter viral shedding and higher recovery rates. Specifically, the Alpha variant showed gradual Ct-up transitions and moderate recovery rates, yielding a presymptomatic recovery index slightly higher than 1 (1.10), whereas the Omicron variant had remarkable Ct-up transitions and significantly higher asymptomatic recovery rates, resulting in a presymptomatic recovery index much higher than 1 (152.5). Sensitivity analysis confirmed the robustness of the chosen Ct values of 18 and 25 across different recovery phases. Regarding the impact of vaccination, individuals without booster vaccination had a 19% higher presymptomatic incidence rate compared to those with booster vaccination. Breakthrough infections in boosted individuals initially showed similar Ct-up transition rates but higher rates in later stages compared to nonboosted individuals. Overall, booster vaccination improved recovery rates, particularly during the symptomatic phase, although recovery rates for persistent asymptomatic infection were similar regardless of vaccination status once the Ct level exceeded 25.

CONCLUSIONS

The study provides new insights into dynamic Ct transitions, with the notable finding that Ct-up transitions toward recovery outpaced Ct-down and symptom-surfacing transitions during the presymptomatic phase. The Ct-up against Ct-down transition varies with variants and vaccination status. The proposed Ct-enshrined compartment model is useful for the surveillance of emerging infectious diseases in the future to prevent community-acquired outbreaks.

New insights into three trajectories of omicron-related all-cause death reduced by COVID-19 booster vaccination

BACKGROUND

The trajectories of all-cause deaths linked to omicron infections are rarely studied, especially in relation to the efficacy of booster shots. For assessing three epidemiological death trajectories, including dying from COVID-19, dying with COVID-19, and non-COVID-19 death, we offer a new COVID-19-and-death competing risk model that deals with the primary pathway (e.g., dying from COVID-19) competing with two other pathways.

METHODS

We applied this model to track three trajectories: deaths directly from COVID-19, deaths with COVID-19 as a contributing factor, and indirect non-COVID-19 deaths. The study used data from a Taiwanese cohort, covering periods of Omicron subvariants BA.2, BA.5, and BA.2.75. It focused on the effectiveness of monovalent and bivalent booster vaccines against these death trajectories.

RESULTS

The highest mortality was observed during the BA.2 phase, which decreased in the BA.5 period and increased again in the BA.2.75 period. Analyzing each trajectory, we noted similar trends in deaths directly from and with COVID-19, while non-COVID-19 deaths remained stable across subvariants. Booster vaccines reduced all-cause mortality by 58% (52%-62%) for BA.2, 70% (65%-75%) for BA.5%, and 75% (70%-80%) for BA.2.75, compared to incomplete vaccination. The reduction in deaths directly from COVID-19 was 66% (61%-72%) for BA.2, 78% (72%-84%) for BA.5%, and 85% (76%-93%) for BA.2.75. For deaths with COVID-19, the figures were 46% (36%-55%), 76% (68%-84%), and 90% (86%-95%). Additionally, the booster shots decreased non-COVID-19 deaths by 64% (63%-66%) for BA.2, 38% (36%-40%) for BA.5, and 19% (17%-21%) for BA.2.75.

CONCLUSION

Our competing risk analysis is effective for monitoring all-cause death trajectories amidst various Omicron infections. It provides insights into the impact of booster vaccines, especially bivalent ones, and highlights the consequences of inadequate healthcare for vulnerable groups.

Protection of COVID-19 Vaccination Against Hospitalization During the Era of Omicron BA.4 and BA.5 Predominance: A Nationwide Case-Control Study Based on the French National Health Data System

Background

Knowing the duration of effectiveness of coronavirus disease 2019 (COVID-19) booster doses is essential to providing decision-makers with scientific arguments about the frequency of subsequent injections. We estimated the level of protection against COVID-19-related hospitalizations (Omicron BA.4-BA.5) over time after vaccination, accounting for breakthrough infections.

Methods

In this nationwide case-control study, all cases of hospitalizations for COVID-19 identified in the comprehensive French National Health Data System between June 1, 2022, and October 15, 2022, were matched with up to 10 controls by year of birth, sex, department, and an individual COVID-19 hospitalization risk score. Conditional logistic regressions were used to estimate the level of protection against COVID-19-related hospitalizations conferred by primary and booster vaccination, accounting for history of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection.

Results

A total of 38 839 cases were matched to 377 653 controls; 19.2% and 9.9% were unvaccinated, respectively, while 68.2% and 77.7% had received ≥1 booster dose. Protection provided by primary vaccination reached 45% (95% CI, 42%-47%). The incremental effectiveness of booster doses ranged from 69% (95% CI, 67%-71%; ≤2 months) to 22% (95% CI, 19%-25%; ≥6 months). Specifically, the second booster provided an additional protection compared with the first ranging from 61% (95% CI, 59%-64%; ≤2 months) to 7% (95% CI, 2%-13%; ≥4 months). Previous SARS-CoV-2 infection conferred a strong, long-lasting protection (51% ≥20 months). There was no incremental effectiveness of a second booster among individuals infected since the first booster.

Conclusions

In the era of Omicron BA.4 and BA.5 predominance, primary vaccination still conferred protection against COVID-19 hospitalization, while booster doses provided an additional time-limited protection. The second booster had no additional protection in case of infection since the first booster.