Postexposure Effects of Vaccines on Infectious Diseases

Post-exposure vaccine effectiveness and contact management in the mpox outbreak, Madrid, Spain, May to August 2022

BackgroundAppropriate vaccination strategies have been key to controlling the outbreak of mpox outside endemic areas in 2022, yet few studies have provided information on mpox vaccine effectiveness (VE).AimTo assess VE after one dose of a third-generation smallpox vaccine against mpox when given as post-exposure prophylaxis (PEP) within 14 days.MethodsA survival analysis in a prospective cohort of close contacts of laboratory-confirmed mpox cases was conducted from the beginning of the outbreak in the region of Madrid in May 2022. The study included contacts of cases in this region diagnosed between 17 May and 15 August 2022. Follow up was up to 49 days. A multivariate proportional hazard model was used to evaluate VE in the presence of confounding and interaction.ResultsInformation was obtained from 484 close contacts, of which 230 were vaccinated within 14 days of exposure. Of the close contacts, 57 became ill during follow-up, eight vaccinated and 49 unvaccinated. The adjusted effectiveness of the vaccine was 88.8% (95% CI: 76.0-94.7). Among sexual contacts, VE was 93.6% (95% CI: 72.1-98.5) for non-cohabitants and 88.6% (95% CI: 66.1-96.2) for cohabitants.ConclusionPost-exposure prophylaxis of close contacts of mpox cases is an effective measure that can contribute to reducing the number of cases and eventually the symptoms of breakthrough infections. The continued use of PEP together with pre-exposure prophylaxis by vaccination and other population-targeted prevention measures are key factors in controlling an mpox outbreak.

Implications for COVID-19 vaccine uptake: A systematic review

BACKGROUND

Globally, increasing coronavirus disease (COVID-19) vaccination coverage remains a major public health concern in the face of high rates of COVID-19 hesitancy among the general population. We must understand the impact of the determinants of COVID-19 vaccine uptake when designing national vaccination programmes. We aimed to synthesise nationwide evidence regarding COVID-19 infodemics and the demographic, psychological, and social predictors of COVID-19 vaccination uptake.

METHODS

We systematically searched seven databases between July 2021 and March 2022 to retrieve relevant articles published since COVID-19 was first reported on 31 December 2019 in Wuhan, China. Of the 12,502 peer-reviewed articles retrieved from the databases, 57 met the selection criteria and were included in this systematic review. We explored COVID-19 vaccine uptake determinants before and after the first COVID-19 vaccine roll-out by the Food and Drug Authority (FDA).

RESULTS

Increased COVID-19 vaccine uptake rates were associated with decreased hesitancy. Concerns about COVID-19 vaccine safety, negative side effects, rapid development of the COVID-19 vaccine, and uncertainty about vaccine effectiveness were associated with reluctance to be vaccinated. After the US FDA approval of COVID-19 vaccines, phobia of medical procedures such as vaccine injection and inadequate information about vaccines were the main determinants of COVID-19 vaccine hesitancy.

CONCLUSION

Addressing effectiveness and safety concerns regarding COVID-19 vaccines, as well as providing adequate information about vaccines and the impacts of pandemics, should be considered before implementation of any vaccination programme. Reassuring people about the safety of medical vaccination and using alternative procedures such as needle-free vaccination may help further increase vaccination uptake.

T cell immunity ameliorates COVID-19 disease severity and provides post-exposure prophylaxis after peptide-vaccination, in Syrian hamsters

Background

The emergence of novel SARS-CoV-2 variants that resist neutralizing antibodies drew the attention to cellular immunity and calls for the development of alternative vaccination strategies to combat the pandemic. Here, we have assessed the kinetics of T cell responses and protective efficacy against severe COVID-19 in pre- and post-exposure settings, elicited by PolyPEPI-SCoV-2, a peptide based T cell vaccine.

Methods

75 Syrian hamsters were immunized subcutaneously with PolyPEPI-SCoV-2 on D0 and D14. On D42, hamsters were intranasally challenged with 10² TCID₅₀ of the virus. To analyze immunogenicity by IFN-γ ELISPOT and antibody secretion, lymphoid tissues were collected both before (D0, D14, D28, D42) and after challenge (D44, D46, D49). To measure vaccine efficacy, lung tissue, throat swabs and nasal turbinate samples were assessed for viral load and histopathological changes. Further, body weight was monitored on D0, D28, D42 and every day after challenge.

Results

The vaccine induced robust activation of T cells against all SARS-CoV-2 structural proteins that were rapidly boosted after virus challenge compared to control animals (~4-fold, p<0.05). A single dose of PolyPEPI-SCoV-2 administered one day after challenge also resulted in elevated T cell response (p<0.01). The vaccination did not induce virus-specific antibodies and viral load reduction. Still, peptide vaccination significantly reduced body weight loss (p<0.001), relative lung weight (p<0.05) and lung lesions (p<0.05), in both settings.

Conclusion

Our study provides first proof of concept data on the contribution of T cell immunity on disease course and provide rationale for the use of T cell-based peptide vaccines against both novel SARS-CoV-2 variants and supports post-exposure prophylaxis as alternative vaccination strategy against COVID-19.

Perception of COVID-19 Booster Dose Vaccine among Healthcare Workers in India and Saudi Arabia

Background: COVID-19 vaccines were made available to the public by the end of 2020. However, little is known about COVID-19 booster dose (CBD) vaccine perception among healthcare workers (HCW) worldwide. The present study aims to assess the perception of CBD vaccines among healthcare workers in India and Saudi Arabia (SA). Methods: A cross-sectional study was conducted among HCWs in two countries, India and SA. Data were gathered through the use of a self-administered questionnaire. A convenience sampling technique was utilized to collect the data. Results: A total of 833 HCW responses were collected from the two countries, with 530 participants from India and 303 participants from SA responding to the questionnaire. Among them, 16% from India and 33% from SA were unwilling to take a CBD (p < 0.005). The primary reasons for not being willing were concerns about whether the vaccine would be effective (32%) and concerns about probable long-term side effects (31%). Concerns about not knowing enough about the vaccination (30%) and the possibility of long-term side effects (28%) were the primary concerns in SA. Regression analysis showed that males, urban residents, and post-graduates were more willing to take the CBD. Conclusion: There is a good perception of CBD and some hesitancy in receiving the booster dose among HCWs in both countries. The introduction of personalized education, risk communication, and deliberate policy could help to reduce the number of people who are unwilling to take a booster shot.

Use of Recently Vaccinated Individuals to Detect Bias in Test-Negative Case-Control Studies of COVID-19 Vaccine Effectiveness

Postauthorization observational studies play a key role in understanding COVID-19 vaccine effectiveness following the demonstration of efficacy in clinical trials. Although bias due to confounding, selection bias, and misclassification can be mitigated through careful study design, unmeasured confounding is likely to remain in these observational studies. Phase III trials of COVID-19 vaccines have shown that protection from vaccination does not occur immediately, meaning that COVID-19 risk should be similar in recently vaccinated and unvaccinated individuals, in the absence of confounding or other bias. Several studies have used the estimated effectiveness among recently vaccinated individuals as a negative control exposure to detect bias in vaccine effectiveness estimates. In this paper, we introduce a theoretical framework to describe the interpretation of such a bias indicator in test-negative studies, and outline strong assumptions that would allow vaccine effectiveness among recently vaccinated individuals to serve as a negative control exposure.

Agent-based modelling of reactive vaccination of workplaces and schools against COVID-19

With vaccination against COVID-19 stalled in some countries, increasing vaccine accessibility and distribution could help keep transmission under control. Here, we study the impact of reactive vaccination targeting schools and workplaces where cases are detected, with an agent-based model accounting for COVID-19 natural history, vaccine characteristics, demographics, behavioural changes and social distancing. In most scenarios, reactive vaccination leads to a higher reduction in cases compared with non-reactive strategies using the same number of doses. The reactive strategy could however be less effective than a moderate/high pace mass vaccination program if initial vaccination coverage is high or disease incidence is low, because few people would be vaccinated around each case. In case of flare-ups, reactive vaccination could better mitigate spread if it is implemented quickly, is supported by enhanced test-trace-isolate and triggers an increased vaccine uptake. These results provide key information to plan an adaptive vaccination rollout.

The authors use an agent-based model to investigate the potential of reactive vaccination strategies for COVID-19 outbreak mitigation. They find that distributing vaccines in schools and workplaces where cases are detected is more impactful than non-reactive strategies in a wide range of epidemic scenarios.

Effectiveness of a third dose of the BNT162b2 mRNA COVID-19 vaccine for preventing severe outcomes in Israel: an observational study

BACKGROUND

Many countries are experiencing a resurgence of COVID-19, driven predominantly by the delta (B.1.617.2) variant of SARS-CoV-2. In response, these countries are considering the administration of a third dose of mRNA COVID-19 vaccine as a booster dose to address potential waning immunity over time and reduced effectiveness against the delta variant. We aimed to use the data repositories of Israel's largest health-care organisation to evaluate the effectiveness of a third dose of the BNT162b2 mRNA vaccine for preventing severe COVID-19 outcomes.

METHODS

Using data from Clalit Health Services, which provides mandatory health-care coverage for over half of the Israeli population, individuals receiving a third vaccine dose between July 30, 2020, and Sept 23, 2021, were matched (1:1) to demographically and clinically similar controls who did not receive a third dose. Eligible participants had received the second vaccine dose at least 5 months before the recruitment date, had no previous documented SARS-CoV-2 infection, and had no contact with the health-care system in the 3 days before recruitment. Individuals who are health-care workers, live in long-term care facilities, or are medically confined to their homes were excluded. Primary outcomes were COVID-19-related admission to hospital, severe disease, and COVID-19-related death. The third dose effectiveness for each outcome was estimated as 1 - risk ratio using the Kaplan-Meier estimator.

FINDINGS

1 158 269 individuals were eligible to be included in the third dose group. Following matching, the third dose and control groups each included 728 321 individuals. Participants had a median age of 52 years (IQR 37-68) and 51% were female. The median follow-up time was 13 days (IQR 6-21) in both groups. Vaccine effectiveness evaluated at least 7 days after receipt of the third dose, compared with receiving only two doses at least 5 months ago, was estimated to be 93% (231 events for two doses vs 29 events for three doses; 95% CI 88-97) for admission to hospital, 92% (157 vs 17 events; 82-97) for severe disease, and 81% (44 vs seven events; 59-97) for COVID-19-related death.

INTERPRETATION

Our findings suggest that a third dose of the BNT162b2 mRNA vaccine is effective in protecting individuals against severe COVID-19-related outcomes, compared with receiving only two doses at least 5 months ago.

FUNDING

The Ivan and Francesca Berkowitz Family Living Laboratory Collaboration at Harvard Medical School and Clalit Research Institute.

Assessing the feasibility of Nipah vaccine efficacy trials based on previous outbreaks in Bangladesh

BACKGROUND

Nipah virus (NiV) is an emerging, bat-borne pathogen that can be transmitted from person-to-person. Vaccines are currently being developed for NiV, and studies have been funded to evaluate their safety and immunogenicity. An important unanswered question is whether it will be possible to evaluate the efficacy of vaccine candidates in phase III clinical trials in a context where spillovers from the zoonotic reservoir are infrequent and associated with small outbreaks. The objective of this study was to investigate the feasibility of conducting a phase III vaccine trial in Bangladesh, the only country regularly reporting NiV cases.

METHODS

We used simulations based on previously observed NiV cases from Bangladesh, an assumed vaccine efficacy of 90% and other NiV vaccine target characteristics, to compare three vaccination study designs: (i) cluster randomized ring vaccination, (ii) cluster randomized mass vaccination, and (iii) an observational case-control study design.

RESULTS

The simulations showed that, assuming a ramp-up period of 10 days and a mean hospitalization delay of 4 days,a cluster-randomized ring vaccination trial would require 516 years and over 163,000 vaccine doses to run a ring vaccination trial under current epidemic conditions. A cluster-randomized mass vaccination trial in the two most affected districts would take 43 years and 1.83 million vaccine doses. An observational case-control design in these two districts would require seven years and 2.5 million vaccine doses.

DISCUSSION

Without a change in the epidemiology of NiV, ring vaccination or mass vaccination trials are unlikely to be completed within a reasonable time window. In this light, the remaining options are: (i) not conducting a phase III trial until the epidemiology of NiV changes, (ii) identifying alternative ways to licensure such as observational studies or controlled studies in animals such as in the US Food and Drug Administration's (FDA) Animal Rule.

Absence of Vaccine-enhanced Disease With Unexpected Positive Protection Against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) by Inactivated Vaccine Given Within 3 Days of Virus Challenge in Syrian Hamster Model

BACKGROUND

Mass vaccination against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is ongoing amidst widespread transmission during the coronavirus disease-2019 (COVID-19) pandemic. Disease phenotypes of SARS-CoV-2 exposure occurring around the time of vaccine administration have not been described.

METHODS

Two-dose (14 days apart) vaccination regimen with formalin-inactivated whole virion SARS-CoV-2 in golden Syrian hamster model was established. To investigate the disease phenotypes of a 1-dose regimen given 3 days prior (D-3), 1 (D1) or 2 (D2) days after, or on the day (D0) of virus challenge, we monitored the serial clinical severity, tissue histopathology, virus burden, and antibody response of the vaccinated hamsters.

RESULTS

The 1-dose vaccinated hamsters had significantly lower clinical disease severity score, body weight loss, lung histology score, nucleocapsid protein expression in lung, infectious virus titers in the lung and nasal turbinate, inflammatory changes in intestines, and a higher serum neutralizing antibody or IgG titer against the spike receptor-binding domain or nucleocapsid protein when compared to unvaccinated controls. These improvements were particularly noticeable in D-3, but also in D0, D1, and even D2 vaccinated hamsters to varying degrees. No increased eosinophilic infiltration was found in the nasal turbinate, lung, and intestine after virus challenge. Significantly higher serum titer of fluorescent foci microneutralization inhibition antibody was detected in D1 and D2 vaccinated hamsters at day 4 post-challenge compared to controls despite undetectable neutralizing antibody titer.

CONCLUSIONS

Vaccination just before or soon after exposure to SARS-CoV-2 does not worsen disease phenotypes and may even ameliorate infection.

The Route of Administration of Rabies Vaccines: Comparing the Data

Cell culture rabies vaccines were initially licensed in the 1980s and are essential in the prevention of human rabies. The first post-exposure prophylaxis (PEP) vaccination regimen recommended by the World Health Organization (WHO) was administered intramuscularly over a lengthy three-month period. In efforts to reduce the cost of PEP without impinging on safety, additional research on two strategies was encouraged by the WHO including the development of less expensive production methods for CCVs and the administration of reduced volumes of CCVs via the intradermal (ID) route. Numerous clinical trials have provided sufficient data to support a reduction in the number of doses, a shorter timeline required for PEP, and the approval of the intradermal route of administration for PEP and pre-exposure prophylaxis (PreP). However, the plethora of data that have been published since the development of CCVs can be overwhelming for public health officials wishing to review and make a decision as to the most appropriate PEP and PreP regimen for their region. In this review, we examine three critical benchmarks that can serve as guidance for health officials when reviewing data to implement new PEP and PreP regimens for their region including: evidence of immunogenicity after vaccination; proof of efficacy against development of disease; and confirmation that the regimen being considered elicits a rapid anamnestic response after booster vaccination.

Modelling of COVID-19 vaccination strategies and herd immunity, in scenarios of limited and full vaccine supply in NSW, Australia

Several vaccines for SARS-CoV-2 are expected to be available in Australia in 2021. Initial supply is limited and will require a judicious vaccination strategy until supply is unrestricted. If vaccines have efficacy as post-exposure prophylaxis (PEP) in contacts, this provides more policy options. We used a deterministic mathematical model of epidemic response with limited supply (age-targeted or ring vaccination) and mass vaccination for the State of New South Wales (NSW) in Australia. For targeted vaccination, the effectiveness of vaccinating health workers, young people and older adults was compared. For mass vaccination, we tested varying vaccine efficacy (VE) and distribution capacities. With a limited vaccine stockpile enough for 1 million people in NSW, if there is efficacy as PEP, the most efficient way to control COVID-19 will be ring vaccination, however at least 90% of contacts per case needs to be traced and vaccinated. Health worker vaccination is required for health system resilience. Age based strategies with restricted doses make minimal impact on the epidemic, but vaccinating older people prevents more deaths. Herd immunity can only be achieved with mass vaccination. With 90% VE against all infection, herd immunity can be achieved by vaccinating 66% of the population. A vaccine with less than 70% VE cannot achieve herd immunity and will result in ongoing risk of outbreaks. For mass vaccination, distributing at least 60,000 doses per day is required to achieve control. Slower rates of vaccination will result in the population living with COVID-19 longer, and higher cases and deaths.

BNT162b2 mRNA Covid-19 Vaccine in a Nationwide Mass Vaccination Setting

BACKGROUND

As mass vaccination campaigns against coronavirus disease 2019 (Covid-19) commence worldwide, vaccine effectiveness needs to be assessed for a range of outcomes across diverse populations in a noncontrolled setting. In this study, data from Israel's largest health care organization were used to evaluate the effectiveness of the BNT162b2 mRNA vaccine.

METHODS

All persons who were newly vaccinated during the period from December 20, 2020, to February 1, 2021, were matched to unvaccinated controls in a 1:1 ratio according to demographic and clinical characteristics. Study outcomes included documented infection with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), symptomatic Covid-19, Covid-19-related hospitalization, severe illness, and death. We estimated vaccine effectiveness for each outcome as one minus the risk ratio, using the Kaplan-Meier estimator.

RESULTS

Each study group included 596,618 persons. Estimated vaccine effectiveness for the study outcomes at days 14 through 20 after the first dose and at 7 or more days after the second dose was as follows: for documented infection, 46% (95% confidence interval [CI], 40 to 51) and 92% (95% CI, 88 to 95); for symptomatic Covid-19, 57% (95% CI, 50 to 63) and 94% (95% CI, 87 to 98); for hospitalization, 74% (95% CI, 56 to 86) and 87% (95% CI, 55 to 100); and for severe disease, 62% (95% CI, 39 to 80) and 92% (95% CI, 75 to 100), respectively. Estimated effectiveness in preventing death from Covid-19 was 72% (95% CI, 19 to 100) for days 14 through 20 after the first dose. Estimated effectiveness in specific subpopulations assessed for documented infection and symptomatic Covid-19 was consistent across age groups, with potentially slightly lower effectiveness in persons with multiple coexisting conditions.

CONCLUSIONS

This study in a nationwide mass vaccination setting suggests that the BNT162b2 mRNA vaccine is effective for a wide range of Covid-19-related outcomes, a finding consistent with that of the randomized trial.

Vaccination for COVID-19 control and considerations for Australia

Vaccines remain the main prospect for an exit strategy from the COVID-19 pandemic, and may, depending on efficacy, duration of protection and uptake, make herd immunity feasible. If herd immunity is not achievable, SARS-COV-2 will circulate long-term. There are many vaccine candidates in development and choices between vaccines that will vary in efficacy and safety. The efficacy of available vaccines is compared and ranges from 62–95% against symptomatic infection with the G614 variant. Efficacy is reduced against new variants of concern and is uncertain against asymptomatic infection. Some vaccines show a better protective immune response than natural infection. The principles of herd immunity and prerequisites for achieving it, such as vaccine efficacy, duration of protection and coverage, are discussed. The alternative vaccine strategies including mass vaccination, targeted risk or age-based vaccination and ring vaccination, as well as speed of vaccination are reviewed. Finally, the impact of variants of concern on vaccine programs and the logistics of mass vaccination are discussed.

The Many Faces of Emerging and Reemerging Infectious Disease

The emergence of disease threats can take many forms, from the adaptation of a traditionally zoonotic pathogen for efficient spread in humans, to the development of antibiotic resistance in well-known pathogens, to the creation of new niches for established disease through social and societal changes. In this commentary, the authors explore these various facets of disease emergence through the lens of the papers included in this issue of Epidemiologic Reviews. The authors explore multiple aspects of emergence and the ways in which emergent pathogens can be controlled with the limited tools available. In doing so, they put the papers in this issue in the context of the broader research agenda around understanding and combatting emergent pathogens.

Targeted Amino Acid Substitution Overcomes Scale-Up Challenges with the Human C5a-Derived Decapeptide Immunostimulant EP67

EP67 is a second-generation, human C5a-derived decapeptide agonist of C5a receptor 1 (C5aR1/CD88) that selectively activates mononuclear phagocytes over neutrophils to potentiate protective innate and adaptive immune responses while potentially minimizing neutrophil-mediated toxicity. Pro7 and N-methyl-Leu8 (Me-Leu8) amino acid residues within EP67 likely induce backbone structural changes that increase potency and selective activation of mononuclear phagocytes over neutrophils versus first-generation EP54. The low coupling efficiency between Pro7 and Me-Leu8 and challenging purification by HPLC, however, greatly increase scale-up costs of EP67 for clinical use. Thus, the goal of this study was to determine whether replacing Pro7 and/or Me-Leu8 with large-scale amenable amino acid residues predicted to induce similar structural changes (cyclohexylalanine7 and/or leucine8) sufficiently preserves EP67 activity in primary human mononuclear phagocytes and neutrophils. We found that EP67 analogues had similar potency, efficacy, and selective activation of mononuclear phagocytes over neutrophils. Thus, replacing Pro7 and/or Me-Leu8 with large-scale amenable amino acid residues predicted to induce similar structural changes is a suitable strategy to overcome scale-up challenges with EP67.