SARS-CoV-2 elicits non-sterilizing immunity and evades vaccine-induced immunity: implications for future vaccination strategies

Investigating the impact of vaccine hesitancy on an emerging infectious disease: a mathematical and numerical analysis

Throughout the last two centuries, vaccines have been helpful in mitigating numerous epidemic diseases. However, vaccine hesitancy has been identified as a substantial obstacle in healthcare management. We examined the epidemiological dynamics of an emerging infection under vaccination using an SVEIR model with differential morbidity. We mathematically analyzed the model, derived R 0 , and provided a complete analysis of the bifurcation at R 0 = 1 . Sensitivity analysis and numerical simulations were used to quantify the tradeoffs between vaccine efficacy and vaccine hesitancy on reducing the disease burden. Our results indicated that if the percentage of the population hesitant about taking the vaccine is 10%, then a vaccine with 94% efficacy is required to reduce the peak of infections by 40%. If 60% of the population is reluctant about being vaccinated, then even a perfect vaccine will not be able to reduce the peak of infections by 40%.

Memory T Cells Subpopulations in a Cohort of COVID-19 Vaccinated or Recovered Subjects

Following viral infection, antigen-restricted T lymphocytes are activated and recognize infected cells to eliminate them. A subset of T cells differentiates into memory lymphocytes able to counteract viral rechallenge in a faster and enhanced way. SARS-CoV-2 can escape immune responses leading to a poor clinical outcome. Immune escape can be associated with the failure of the development of T cell memory compartments. The aim of this study is to characterize the T memory subsets and to test the immune response against class I- and II-restricted immunodominant epitopes shared by ancestral and SARS-CoV-2 variants strains. T memory subsets and recognition of SARS-CoV-2S Spike-specific epitopes were analyzed by flow cytometry on 14 fully vaccinated healthy donors (HDV) and 18 COVID-19 recovered patients (CD). The results obtained showed that CD8+ T naïve subset numbers decreased in association with a significant increase of the effector memory T cell subset whereas there was a small increase in the percentage of SARS-CoV-2 antigen-restricted T clones in both CD4+ and CD8+ subset in the CD compared to HDV sample. Collectively, these features may reflect a broader cytotoxic T cell repertoire stimulated by the virus during the natural infection compared to the spike-restricted response activated during vaccination.

Indirect effectiveness of a novel SARS-COV-2 vaccine (SCB-2019) in unvaccinated household contacts in the Philippines: A cluster randomised analysis

BACKGROUND

Though observational evidence supports indirect effects of SARS-CoV-2 vaccines, randomised experiments are lacking. To address this gap, the double-blinded, prospective follow-up of the household contacts (HHCs) of Philippine participants of the individually-randomised, placebo-controlled trial of the adjuvanted-subunit protein COVID-19 vaccine, SCB-2019, (EudraCT, 2020-004272-17; ClinicalTrials.gov, NCT04672395) was analyzed in a cluster-randomised fashion.

METHODS

Over an eight-week period, HHCs were followed by rRT-PCR and paired rapid antibody tests (RATs) to detect symptomatic (SCI, primary) and all (ACI, secondary) SARS-CoV-2 infection. A standard analysis estimated the indirect effectiveness of SCB-2019 for each endpoint, excluding HHC RAT-positive at enrollment. A secondary analysis employed enzyme-linked immunosorbent assay (ELISA) results to correct for suspected bias.

FINDINGS

SCB-2019 (N = 3470) and placebo (N = 3225) exposed HHCs contributed to at least one analysis. The standard analysis estimated that SCB-2019 reduced the risk of SCI by 83% (95% confidence/credible interval [CI: 32% to 96%), with no effect against ACI. The bias-corrected relative risk reduction was 97% (95% CI: 74% to 100%) for SCI and 79% (95% CI: 14% to 96%) for ACI, with an estimated one SARS-CoV-2 infection prevented per 4.8 households where one member received SCB-2019.

INTERPRETATION

SCB-2019 demonstrated bias-corrected indirect effectiveness against SARS-CoV-2 infection among HHC, even at a modest coverage level in the household (approximately 25%). Further research into the indirect effects of SARS-CoV-2 vaccines is needed to optimize the impact of limited doses in low and middle-income settings.

Age-Related Differences in Neutralizing Antibody Responses against SARS-CoV-2 Delta and Omicron Variants in 151 SARS-CoV-2-Naïve Metropolitan Residents Boosted with BNT162b2

BACKGROUND

Although age negatively correlates with vaccine-induced immune responses, whether the vaccine-induced neutralizing effect against variants of concern (VOCs) substantially differs across age remains relatively poorly explored. In addition, the utility of commercial binding assays developed with the wild-type SARS-CoV-2 for predicting the neutralizing effect against VOCs should be revalidated.

METHODS

We analyzed 151 triple-vaccinated SARS-CoV-2-naïve individuals boosted with BNT162b2 (Pfizer-BioNTech). The study population was divided into young adults (age < 30), middle-aged adults (30 ≤ age < 60), and older adults (age ≥ 60). The plaque reduction neutralization test (PRNT) titers against Delta (B.1.617.2) and Omicron (B.1.1.529) variants were compared across age. Antibody titers measured with commercial binding assays were compared with PRNT titers.

RESULTS

Age-related decline in neutralizing titers was observed for both Delta and Omicron variants. Neutralizing titers for Omicron were lower than those against Delta in all ages. The multiple linear regression model demonstrated that duration from third dose to sample collection and vaccine types were also significant factors affecting vaccine-induced immunity along with age. The correlation between commercial binding assays and PRNT was acceptable for all age groups with the Delta variant, but relatively poor for middle-aged and older adults with the Omicron variant due to low titers.

CONCLUSIONS

This study provides insights into the age-related dynamics of vaccine-induced immunity against SARS-CoV-2 VOCs, corroborating the need for age-specific vaccination strategies in the endemic era where new variants continue to evolve. Moreover, commercial binding assays should be used cautiously when estimating neutralizing titers against VOCs, particularly Omicron.

A pan-influenza monoclonal antibody neutralizes H5 strains and prophylactically protects through intranasal administration

Avian A(H5N1) influenza virus poses an elevated zoonotic threat to humans, and no pharmacological products are currently registered for fast-acting pre-exposure protection in case of spillover leading to a pandemic. Here, we show that an epitope on the stem domain of H5 hemagglutinin is highly conserved and that the human monoclonal antibody CR9114, targeting that epitope, potently neutralizes all pseudotyped H5 viruses tested, even in the rare case of substitutions in its epitope. Further, intranasal administration of CR9114 fully protects mice against A(H5N1) infection at low dosages, irrespective of pre-existing immunity conferred by the quadrivalent seasonal influenza vaccine. These data provide a proof-of-concept for broad, pre-exposure protection against a potential future pandemic using the intranasal administration route. Studies in humans should assess if autonomous administration of a broadly-neutralizing monoclonal antibody is safe and effective and can thus contribute to pandemic preparedness.

Responses to Common Misconceptions Relating to COVID-19 Variant-Adapted mRNA Vaccines

The evolution of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the waning of immunity over time has necessitated the use of booster doses of original coronavirus disease 2019 (COVID-19) vaccines. This has also led to the development and implementation of variant-adapted messenger RNA (mRNA) vaccines that include an Omicron sub-lineage component in addition to the antigen based on the wild-type virus spike protein. Subsequent emergence of the recombinant XBB sub-lineages triggered the development of monovalent XBB-based variant-adapted mRNA vaccines, which are available for vaccination campaigns in late 2023. Misconceptions about new variant-adapted vaccines may exacerbate vaccine fatigue and drive the lack of vaccine acceptance. This article aims to address common concerns about the development and use of COVID-19 variant-adapted mRNA vaccines that have emerged as SARS-CoV-2 has continued to evolve.

Long-term vaccination strategies to mitigate the impact of SARS-CoV-2 transmission: A modelling study

BACKGROUND

Vaccines have reduced severe disease and death from Coronavirus Disease 2019 (COVID-19). However, with evidence of waning efficacy coupled with continued evolution of the virus, health programmes need to evaluate the requirement for regular booster doses, considering their impact and cost-effectiveness in the face of ongoing transmission and substantial infection-induced immunity.

METHODS AND FINDINGS

We developed a combined immunological-transmission model parameterised with data on transmissibility, severity, and vaccine effectiveness. We simulated Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) transmission and vaccine rollout in characteristic global settings with different population age-structures, contact patterns, health system capacities, prior transmission, and vaccine uptake. We quantified the impact of future vaccine booster dose strategies with both ancestral and variant-adapted vaccine products, while considering the potential future emergence of new variants with modified transmission, immune escape, and severity properties. We found that regular boosting of the oldest age group (75+) is an efficient strategy, although large numbers of hospitalisations and deaths could be averted by extending vaccination to younger age groups. In countries with low vaccine coverage and high infection-derived immunity, boosting older at-risk groups was more effective than continuing primary vaccination into younger ages in our model. Our study is limited by uncertainty in key parameters, including the long-term durability of vaccine and infection-induced immunity as well as uncertainty in the future evolution of the virus.

CONCLUSIONS

Our modelling suggests that regular boosting of the high-risk population remains an important tool to reduce morbidity and mortality from current and future SARS-CoV-2 variants. Our results suggest that focusing vaccination in the highest-risk cohorts will be the most efficient (and hence cost-effective) strategy to reduce morbidity and mortality.

Retained avidity despite reduced cross-binding and cross-neutralizing antibody levels to Omicron after SARS-COV-2 wild-type infection or mRNA double vaccination

Introduction

The rapid evolution of SARS-CoV-2 has posed a challenge to long-lasting immunity against the novel virus. Apart from neutralizing function, binding antibodies induced by vaccination or infection play an important role in containing the infection.

Methods

To determine the proportion of wild-type (WT)-generated antibodies recognizant of more recent variants, plasma samples from either SARS-CoV-2 WT-infected (n = 336) or double-mRNA (Comirnaty)-vaccinated individuals (n = 354, age and sex matched to the convalescent group) were analyzed for binding antibody capacity against the S1 protein of the BA.1 omicron variant.

Results

Overall, 38.59% (95% CI, 37.01- 40.20) of WT-generated antibodies recognized Omicron BA.1 S1 protein [28.83% (95% CI, 26.73-30.91) after infection and 43.46% (95% CI, 41.61-45.31) after vaccination; p < 0.001]. Although the proportion of WT-generated binding and neutralizing antibodies also binding to BA.1 is substantially reduced, the avidity of the remaining antibodies against the Omicron variant was non-inferior to that of the ancestral virus: Omicron: 39.7% (95% CI: 38.1-41.3) as compared to the avidity to WT: 27.0% (95% CI, 25.5-28.4), respectively (p < 0.001). Furthermore, we noticed a modestly yet statistically significant higher avidity toward the Omicron epitopes among the vaccinated group (42.2%; 95% CI, 40.51-43.94) as compared to the convalescent counterparts (36.4%; 95% CI, 33.42-38.76) (p = 0.003), even after adjusting for antibody concentration.

Discussion

Our results suggest that an aspect of functional immunity against the novel strain was considerably retained after WT contact, speculatively counteracting the impact of immune evasion toward neutralization of the strain. Higher antibody levels and cross-binding capacity among vaccinated individuals suggest an advantage of repeated exposure in generating robust immunity.

Study of optimal vaccination strategies for early COVID-19 pandemic using an age-structured mathematical model: A case study of the USA

In this paper we study different vaccination strategies that could have been implemented for the early COVID-19 pandemic. We use a demographic epidemiological mathematical model based on differential equations in order to investigate the efficacy of a variety of vaccination strategies under limited vaccine supply. We use the number of deaths as the metric to measure the efficacy of each of these strategies. Finding the optimal strategy for the vaccination programs is a complex problem due to the large number of variables that affect the outcomes. The constructed mathematical model takes into account demographic risk factors such as age, comorbidity status and social contacts of the population. We perform simulations to assess the performance of more than three million vaccination strategies which vary depending on the vaccine priority of each group. This study focuses on the scenario corresponding to the early vaccination period in the USA, but can be extended to other countries. The results of this study show the importance of designing an optimal vaccination strategy in order to save human lives. The problem is extremely complex due to the large amount of factors, high dimensionality and nonlinearities. We found that for low/moderate transmission rates the optimal strategy prioritizes high transmission groups, but for high transmission rates, the optimal strategy focuses on groups with high CFRs. The results provide valuable information for the design of optimal vaccination programs. Moreover, the results help to design scientific vaccination guidelines for future pandemics.