Human Influenza Virus Infections
Sunit K. Singh in Human Respiratory Viral Infections, 2014
LAIV is extremely effective in vaccine-naive children, in whom vaccine efficacy ranges from 73% to 96% after the first immunization, and from 82% to 100% after revaccination.273 Vaccine efficacy may decrease in people who have been repeatedly infected with influenza during their lifetime because they may have some preexisting immunity toward the vaccine. LAIV is less effective in eliciting serum anti-HA antibody responses, but does induce the production of mucosal antibodies, which could contribute to both long-term maintenance of immunity and cross-protection among different strains of influenza virus.274 Randomized studies that directly compared the efficacy of TIV and LAIV showed that LAIV consistently confers approximately 50% greater protection than TIV in young children 12–59 months in age.275,276 In studies performed in adults, TIV efficacy was either comparable or slightly superior to LAIV.265
Sample Size for HIV-1 Vaccine Clinical Trials with Extremely Low Incidence Rate
Cliburn Chan, Michael G. Hudgens, Shein-Chung Chow in Quantitative Methods for HIV/AIDS Research, 2017
The goal of a preventive HIV vaccine is to induce cell-mediated immune (CMI) responses and subsequently to reduce the plasma viral load at set point and preserve memory CD4+ lymphocytes. As a result, clinical efforts have mainly focused on CMI-inducing vaccines such as DNA and vectors alone or in prime-boost regimens (Belyakov et al. 2008; Esteban 2009). In a recent Thai efficacy trial (RV144), the data revealed the first evidence that HIV-1 vaccine protection against HIV-1 acquisition could be achieved. The results of RV144 indicated that patients with the lowest risk (yearly incidence of 0.23/100 person-years) had an apparent efficacy of 40%, whereas those with the highest risk (incidence of 0.36/100 person-years) had an efficacy of 3.7%. This finding suggested that clinical meaningful difference in vaccine efficacy can be detected by means of the difference in the incidence of risk rate. In addition, the vaccine efficacy appeared to decrease with time (e.g., at 12 months, the vaccine efficacy was about 60% and fell to 29% by 42 months). As a result, at a specific time point, the sample size required for achieving a desired vaccine efficacy can be obtained by detecting a clinically meaningful difference in the incidence of the risk rate at baseline.
Neurological events following immunizations
Avindra Nath, Joseph R. Berger in Clinical Neurovirology, 2020
There are several important determinants of vaccine efficacy, which modulate the intensity of peak antibody responses. The nature of the vaccine antigen and its intrinsic immunogenicity are important, with some antigens being inherently more immunogenic than others. Live vaccines generally elicit stronger innate immune responses and thus stronger antibody responses. Non-live vaccines frequently require the use of adjuvants, or agents which increase the stimulation of the immune system by enhancing antigen presentation; aluminum salts are frequently used as adjuvants [18]. Many vaccines, particularly inactivated vaccines, require multiple doses to induce high and sustained antibody responses, or may require repeated administration at particular intervals. Antibody persistence is critically important; for the vaccine immune response to last, memory B cells, which are capable of recognizing and responding to an antigen challenge and subsequently proliferating and differentiating into antibody producing plasma cells, must be produced. Antibody persistence may be dependent on several different determinants, including the nature of the vaccine (live vs. inactivated), interval between doses, and age at immunization.
Severe mental disorders and vaccinations – a systematic review
Published in The World Journal of Biological Psychiatry, 2022
Nina Bonkat, Frederike T. Fellendorf, Nina Dalkner, Eva Z. Reininghaus
The purpose of vaccinations is to prevent severe, life-threatening infections such as pneumococcal disease, hepatitis B and tuberculosis. In December 2020, the first vaccines against the SARS-CoV-2 virus were approved. Vaccines influence the immune system mostly by stimulating the formation of antibodies, but can also evoke a T-cell response. Vaccine immunogenicity is the ability of a vaccine to elicit an immune response and can be determined by measuring antibody titres. In contrast, vaccine efficacy is the ability to protect the vaccinated individual from infection and can be measured by the risk reduction of infection in vaccinated individuals in a controlled clinical trial (Banaszkiewicz and Radzikowski 2013). However, it has been suggested that individuals with SMI have an impaired response to vaccinations influenced by their chronic pro-inflammatory profiles, as well as impaired adaptive immune systems. Additionally, efficacy and side effects of vaccinations might be different in individuals with SMI compared with the general population. Psychopharmacological treatment might also affect the response of vaccinations.
COVID-19 vaccine effectiveness among immunocompromised populations: a targeted literature review of real-world studies
Published in Expert Review of Vaccines, 2022
Manuela Di Fusco, Jay Lin, Shailja Vaghela, Melissa Lingohr-Smith, Jennifer L. Nguyen, Thomas Scassellati Sforzolini, Jennifer Judy, Alejandro Cane, Mary M. Moran
As of 30 September 2021 approximately 45% of the worldwide population had received at least one dose of a coronavirus disease 2019 (COVID-19) vaccine [1]. Scientific evidence gained from real-world studies conducted in multiple countries is increasingly showing that widely available COVID-19 vaccines, including BNT162b2 (Pfizer/BioNTech), mRNA-1273 (Moderna), Ad26.COV2.S (Janssen), and ChAdOx1 nCoV-19 (Oxford/AstraZeneca), are effective against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, symptomatic COVID-19 illness, and COVID-19-related hospitalization and death [2,3]. Such findings from real-world studies are generally consistent with the efficacy results of the randomized clinical trials (RCTs) of these vaccines [4–7]. Vaccine efficacy in clinical trials and vaccine effectiveness (VE) measured in real-world studies both calculate the risk of disease among vaccinated and unvaccinated individuals and the percentage reduction in risk of disease among vaccinated individuals relative to unvaccinated individuals; VE equates to the reduction in disease occurrence for those who are vaccinated (i.e. a VE of 85% = an 85% reduction in disease occurrence among the vaccinated) [8].
COVID-19 vaccines: concerns beyond protective efficacy and safety
Published in Expert Review of Vaccines, 2021
Chih-Cheng Lai, I-Tzu Chen, Chien-Ming Chao, Ping-Ing Lee, Wen-Chien Ko, Po-Ren Hsueh
Gam-COVID-Vac is a combined vector vaccine based on rAd type 26 (rAd26) and rAd type 5 (rAd5), both of which carry the gene for SARS-CoV-2 full-length glycoprotein S (rAd26-S and rAd5-S). Phase 1–2 clinical trials involving 76 participants showed that this vaccine was well tolerated and highly immunogenic in healthy participants [37]. An interim analysis of a phase 3 RCT in Russia reported that 16 (0.1%) of the 14,964 participants in the vaccine group and 62 (1.3%) of the 4,902 participants in the placebo group had confirmed COVID-19 21 days after the first dose. Thus, the vaccine’s overall vaccine efficacy was 91.6% (95% CI, 85.6% – 95.2%) [18]. The observed vaccine efficacy was over 87% for all age and sex subgroups. Because zero (vaccine group) and 20 individuals (placebo group) had moderate or severe COVID-19 at least 21 days after the first dose, the vaccine efficacy against moderate or severe COVID-19 was 100% (95% CI, 94.4% – 100.0%). In this study, of the 16,427 participants in the vaccine group, 45 (0.3%) experienced serious adverse events, and 3 (< 0.1%) died, but these deaths were unrelated to the vaccine [18].
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