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PubMed2026

Ethiopia missed opportunities for vaccination study: Cluster-randomized evaluation of 5-dose measles vaccine vials and a flexible open-vial policy, 2021-2022.

INTRODUCTION: In 2024, an estimated 95,000 people died from measles globally, largely from suboptimal coverage with the measles-containing vaccine (MCV). Health workers may defer vaccinating eligible children to avoid wasting doses from 10-dose MCV vials, which must be discarded six hours after opening. These missed opportunities for vaccination (MOV) reduce coverage and timeliness. Ethiopia, which provides MCV at 9 and 15 months, considered switching to 5-dose vials. METHODS: We conducted a 15-month, randomized controlled trial with a nested cross-sectional design in Ethiopia. Sixty woredas were randomized to: (1) policy-only, instructing health workers to open 10-dose vials for any number of eligible children, with additional stock for increased wastage; (2) 5-dose switch, combining this policy with replacement of 10-dose by 5-dose vials; or (3) control (routine 10-dose practice). Household and health-facility surveys at baseline and endline assessed effects on first-dose (MCV1) and second-dose (MCV2) coverage, MCV1 timeliness, and wastage. Generalized estimating equation models estimated net intervention effects versus control. We also estimated the government cost of a nationwide 5-dose switch. RESULTS: MCV1 coverage was similar between policy-only and control (adjusted risk difference [ARD] = -1%, 95%CI: -17%, 15%), with no significant differences in MCV1 timeliness or MCV2 coverage. In the 5-dose switch group, MCV1 coverage changed little (ARD = 1%, 95%CI: -17%, 18%), but timely MCV1 at 9 months (ARD = 18%, 95%CI: 7%, 28%) and MCV2 coverage (ARD = 17%, 95%CI: 1%, 34%) rose significantly, and wastage fell (ARD = -7%, 95%CI: -14%, -1%). By endline, 29% of 5-dose health workers opened vials ≥10 times monthly (none in control); caregivers in both intervention groups reported 11% fewer measles-related MOVs. A nationwide 5-dose switch was estimated to save 17% in procurement cost per fully vaccinated (two-dose) child. CONCLUSIONS: The combined 5-dose intervention improved MCV1 timeliness and MCV2 coverage and reduced wastage, addressing a key operational barrier and potentially supporting measles elimination in Ethiopia.

Humans↗

PubMed2026

Stroke risk following BNT162b2 vaccination: a systematic review and meta-analysis of self-controlled case series studies.

INTRODUCTION: Whether BNT162b2 (Pfizer-BioNTech) vaccination increases stroke risk remains a public health concern. This is the first meta-analysis to synthesize self-controlled case series (SCCS)-derived stroke risk estimates specifically for BNT162b2 vaccination. METHODS: PubMed and Embase were searched from inception through 9 May 2026, following PRISMA 2020 guidelines. Eight eligible SCCS studies were pooled using a random-effects model with restricted maximum likelihood (REML) estimation and the Knapp-Hartung adjustment. RESULTS: Eight studies across six countries encompassing several million vaccinated individuals were included. The pooled incidence rate ratio (IRR) was 0.967 (95% CI 0.892-1.049; I2 = 69.2%), indicating no statistically significant increase in stroke risk. Subgroup analyses showed no evidence of effect modification across continent, risk-window length, dose category, SCCS variant, or age group. CONCLUSIONS: These findings provide no evidence of increased short-term stroke risk following BNT162b2 vaccination at the population level. The observed heterogeneity appeared to be partly driven by methodological differences rather than true biological variation in vaccine effect.

Humans↗

PubMed2026

2024-2025 BNT162b2 KP.2 COVID-19 full season vaccine effectiveness from vaccine registries linked to administrative claims in two states: A cohort study in non-immunocompromised adults.

BACKGROUND: Data on effectiveness of COVID-19 vaccinations during the 2024-2025 respiratory season are limited, particularly among those with underlying medical conditions (UMC). We estimated BNT162b2 KP.2 vaccine effectiveness (VE) against COVID-19-associated hospital admission, emergency department (ED), and urgent care (UC) visits in two U.S. states. METHODS: Retrospective cohort study of non-immunocompromised adults living in Louisiana or California, with ≥1 year prior continuous enrollment in insurance plans contributing to the HealthVerity claims database beginning August 22, 2024. The effectiveness of BNT162b2 KP.2 vaccine (2024-2025 formulation, hereafter referred to as BNT162b2), measured as a time-varying exposure against hospital admission, ED, or UC encounters with International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM) code U07.1 was calculated as 1 - adjusted hazard ratio using Cox proportional hazard models adjusted for age group, sex, state, insurance payor, presence or absence of UMCs, and pre-index healthcare utilization. Stratifications included those aged 65 years and older, those aged 18-64 years with UMCs, and those aged 18-64 years without UMCs. RESULTS: The cohort included 6,256,421 individuals (93% California, 7% Louisiana); 330,565 (5%) received the BNT162b2 vaccine. Vaccinated individuals were older and had more comorbidities, wellness visits, and prior influenza vaccination. Overall, 66% of the study population had ≥1 UMC; the most prevalent conditions were obesity (25%), history of immunocompromised conditions (23%), and mental health conditions (19%). COVID-19-related encounter rates for ED, UC or hospitalization were lower among vaccinated compared to unvaccinated persons (25.1 vs 36.3 per 100,000 person-months). Among all adults, VE was 37% against hospitalization, 12% against ED/UC encounters, and 16% against ED/UC/hospitalization encounters. Results were similar across age groups and UMCs. CONCLUSIONS: BNT162b2 provided protection against COVID-19-associated outcomes of ED, UC or hospitalization among non-immunocompromised U.S. adults, including those with UMCs, over the course of the 2024-2025 respiratory virus season, supporting continued vaccine recommendations. REGISTRATION: This study was posted on clinicaltrials.gov prior to analyses (NCT06923137).

Adolescent↗

PubMed2025

Exploring determinants of vaccine hesitancy among healthcare professionals: a systematic literature review.

INTRODUCTION: This systematic review aims to assess determinants of vaccine hesitancy (VH) among healthcare professionals, to identify knowledge gaps and inform targeted training programs. RESEARCH DESIGN AND METHODS: A systematic search of PubMed and Scopus was conducted in February 2024. PRISMA criteria were applied, and methodological quality was assessed using a cross-sectional study evaluation tool. Studies addressing HCWs' VH determinants, including knowledge, attitudes, communication, and organizational factors, were included. RESULTS: Out of 1394 records, 221 articles were included. Reported prevalence of VH among HCWs varied across studies, reflecting differences in professional roles, settings, and vaccines studied. Key determinants included gaps in knowledge, personal beliefs, organizational barriers, and communication skills. The review highlights the importance of evidence-based information, continuing education, and effective communication in addressing VH among HCWs. CONCLUSIONS: Educational and organizational interventions are essential to improve HCWs' knowledge, attitudes, and practices regarding vaccination. Strengthening vaccine education, fostering effective communication, and addressing organizational challenges can reduce hesitancy and support HCWs in promoting vaccination among patients. Future initiatives should consider the diversity of educational settings, professional roles, and training requirements across healthcare systems.

Humans↗

PubMed2026

Approaches to observational study designs and analytical options to evaluate the safety of multi-dose vaccines: a systematic review.

INTRODUCTION: Observational studies require careful considerations when evaluating the safety of multidose vaccines. We reviewed design and analytical approaches in observational studies evaluating the safety of multidose vaccines in the post-licensure phase. METHODS: EMBASE, MEDLINE, Web of Science, and Scopus (2018-2022) were searched for hypothesis-testing studies evaluating the safety of multidose vaccines. Key features from frequently used designs were extracted. RESULTS: Among 123 eligible studies, cohort (46%) and self-controlled case series (SCCS)/self-controlled risk interval (SCRI) (40%) followed by case-control (12%) were the most common designs, and 15% of studies used multiple designs. Among cohort studies evaluating multiple doses, vaccination date (36%) and cohort entry with time-updated exposure status (32%) were frequent approaches used to define time zero. Twenty-eight percent of cohort studies did not report time zero; all but one evaluated COVID-19 vaccine effect on post-delivery and fertility-related outcomes. For SCCS/SCRI, 64% of studies accounted for event-dependent exposures, mainly by including pre-exposure periods (53%) and modified SCCS model (48%), while 20% employed multiple correction strategies. Among studies using multiple designs, 68% reached consistent conclusions. CONCLUSIONS: SCCS/SCRI and cohort designs dominate multidose vaccine safety studies. Clear reporting on time zero in pregnancy and fertility-related cohort studies, and on addressing event-dependent exposures in SCCS/SCRI studies is needed, along with guidance on interpreting results from multiple designs.

Humans↗

PubMed2026

Safety of a quadrivalent meningococcal conjugate vaccine (MenACYW-TT) administered concomitantly with routine pediatric vaccines in healthy infants and toddlers in USA and Puerto Rico: Results from a Phase III, randomized, active-controlled study.

MenACYW-TT, a quadrivalent meningococcal tetanus toxoid-conjugate vaccine, is approved for prevention of invasive meningococcal disease in infants ≥ 6 weeks of age in the USA. This Phase III study (NCT03673462; September 17, 2018 - March 16, 2023) evaluated the safety of MenACYW-TT compared with a licensed quadrivalent meningococcal oligosaccharide diphtheria CRM197-conjugate vaccine (MenACWY-CRM) when administered concomitantly with routine pediatric vaccines in healthy infants and toddlers in a four-dose series (3+1 schedule). Participants were randomized 3:1 to receive MenACYW-TT (Group 1; n = 2080) or MenACWY-CRM (Group 2; n = 697) at 2, 4, 6, and 12 months of age, with concomitant administration of routine pediatric vaccines (DTaP5-IPV/Hib, PCV13, rotavirus, hepatitis B, MMR, and varicella vaccines). Safety assessments included immediate unsolicited adverse events within 30 minutes post-vaccination, solicited injection site and systemic reactions within 7d, unsolicited AEs within 30d, serious adverse events (SAEs) including adverse events of special interest (AESIs), and medically attended adverse events (MAAEs) throughout the study. MenACYW-TT and MenACWY-CRM were overall well tolerated, and safety profiles were comparable. Solicited injection site reactions occurred in 84.9% and 84.6% of participants in Groups 1 and 2, respectively; solicited systemic reactions in 87.1% and 88.2%, respectively. During the entire study, 5.2% in Group 1 and 3.0% in Group 2 experienced at least one SAE; 0.9% and 0.1%, respectively, reported at least one AESI. Three deaths occurred in Group 1. All SAEs, AESIs, and deaths were unrelated to study vaccines. This study supports the safety profile of MenACYW-TT in infants and toddlers aged ≥ 6 weeks.Study registration: Clinicaltrials.gov: NCT03673462; EudraCT: 2019-004459-35.

Child, Preschool↗

PubMed2026

Dengue and chikungunya vaccines past, present and future: implications for travelers.

PURPOSE OF REVIEW: Novel vaccines for dengue and chikungunya viruses offer new prevention options against two globally important arboviral diseases. This review summarizes recent developments in vaccine licensure, implementation, real-world experience and research priorities, with emphasis on implications for both endemic populations and travelers. RECENT FINDINGS: Of the three live-attenuated dengue vaccines licensed to date, TAK-003 is authorized in >40 countries and Butantan-DV in Brazil, while manufacturing of CYD-TDV is discontinued. Long-term and postmarketing data continue to refine understanding of serotype-specific protection, waning immunity, and rare adverse events.For chikungunya, two single-dose vaccines are licensed-a live-attenuated vaccine (VLA1553) and virus-like particle vaccine (PXVX0317). Uptake is guided by emerging safety and effectiveness data, with each platform offering potential advantages in different settings.Further data on long-term protection, safety, effectiveness, use in vulnerable populations and integration into outbreak management and immunization systems is anticipated. SUMMARY: Dengue and chikungunya vaccines are increasingly being used in immunization programs and pretravel consultations. Further real-world data are needed-particularly for seronegative dengue vaccine recipients and older, immunocompromised or medically at-risk adults. Research priorities include developing single-dose, nonlive dengue vaccines suitable for high-risk groups, understanding long-term chikungunya vaccine performance, and exploring broader flaviviral or pan-arboviral platforms.

Humans↗

PubMed2026

Comparison of immunogenicity, safety, and efficacy of EVA71 vaccine in children: a systematic review and meta-analysis.

INTRODUCTION: Enterovirus 71 (EV-A71) is a principal cause of hand, foot, and mouth disease (HFMD), potentially leading to severe neurological complications in children. Inactivated EV-A71 vaccines have been introduced. This study compares the immunogenicity, safety, and efficacy of EV-A71 vaccines versus placebo in pediatric populations. RESEARCH DESIGN AND METHODS: Following a PROSPERO-registered protocol, RCTs involving EV-A71 in children were identified via PubMed, Scopus, Cochrane, and ClinicalTrials.gov. Two independent reviewers performed screening, extraction, and RoB assessments (RoB 2.0). RESULTS: Five phase III RCTs involving 36,659 children were included. EV-A71 vaccination significantly increased seropositivity across follow-up periods, including early (RR 5.8), medium-term (RR 3.09), and long-term (RR 2.95) response. Seroconversion was significantly higher in the vaccinated group (pooled RR 13.04, 95% CI 2.80-60.61; p < 0.001). Geometric mean titers, analyzed using the ratio of means approach, were significantly higher in the vaccinated group during early and medium-term follow-up. Vaccine efficacy against EV-A71-associated HFMD exceeded 98% (pooled RR 0.02, 95% CI 0.01-0.09; p = 0.0028; I2 = 50%). Solicited local and systemic adverse events were mild and comparable between groups. CONCLUSION: Inactivated EV-A71 vaccines robust immunogenicity, high clinical efficacy, and an acceptable safety profile in children. Future studies should explore long-term protection, booster schedules, and multivalent formulations against non-EV-A71 serotypes.

Humans↗

PubMed2026

Molecular characterization of 16 MAPK genes in silver carp (Hypophthalmichthys molitrix) and the differences of their mRNA expression between Qiandao Lake and Taihu Lake.

Mitogen-activated protein kinase (MAPK), a serine-threonine protein kinase, is involved in a variety of stress-induced responses and also plays an important regulatory role in cell metabolism. In the study the open reading frames (ORFs) of 16 MAPK genes in silver carp (Hypophthalmichthys molitrix) were obtained and verified, with the evaluations of their taxonomy, structures, conserved motifs, and evolutionary linkages. And the expression patterns of these genes in the silver carp from Qiandao Lake and Taihu Lake were explored for better understanding the response of MAPK genes to different water environment. MAPK genes of silver carp were divided into three subfamilies, including extracellular signal-regulated kinase (ERK) subfamily, p38 subfamily and C-Jun N-terminal kinase (JNK) subfamily. All these genes possessed similar structures and conserved motifs of MAPK family. Realtime qPCR revealed that the expression patterns of 10 MAPK genes (ScMAPK1, ScMAPK3, ScMAPK4, ScMAPK7, ScMAPK15, ScMAPK8a, ScMAPK8b, ScMAPK9, ScMAPK10 and ScMAPK11) in head kidney, spleen and gill of silver carp in Taihu Lake and Qiandao Lake were different. These findings provide a basis for further research on the function of MAPK in silver carp.

Animals↗

PubMed2026

A multi-center, open-labelled, randomized controlled extended phase III non-inferiority clinical trial to evaluate the immunogenicity and tolerability of poliomyelitis vaccine (Vero cells), inactivated, Sabin strains administered with or without routine infant vaccines.

BACKGROUND: Oral poliovirus vaccine (OPV) has been reported to cause vaccine-derived poliovirus and vaccine-associated paralytic poliomyelitis, and the limited global supply of conventional IPV has led many countries to rely on fractional-dose IPV regimens alongside OPV. The current study aims to assess the sIPV safety and immunogenicity when given concurrently with or in a staggered manner with routine immunization. METHODS: A multi-country, multi-center, open-label, randomized controlled, extended phase III non-inferiority clinical trial was conducted with 1442 healthy infants aged 6-8 weeks from Bangladesh and Pakistan enrolled and randomized into four groups, i.e., co-administration group 1 (group C1), co-administration group 2 (group C2), staggered administration group 1 (group S1) and staggered administration group 2 (group S2). Antibody levels were determined using the collected sera for immunogenicity evaluation. The difference in seroconversion rates between the coadministration group and the staggered administration group is compared using the Cochran-Mantel-Haenszel χ2 (CMH-χ2) test, stratified by study site. Non-inferiority is concluded if the lower bound of the 95% confidence interval (CI) for the rate difference (coadministration group minus staggered administration group) is greater than -10%. The trial was registered prior to patient enrollment at clinicaltrials.gov (NCT05850364), and the protocol and statistical analysis plan are available at https://clinicaltrials.gov/study/NCT05850364. The trial is closed to new participants. FINDINGS: The post-vaccination seroconversion rates for PV I were 90.3% (306/339) in group C1 and 87.0% (261/300) in group S1, for PV II, 91.7% (311/339) in group C1 and 91.3% (274/300) in group S1 and for PV III, 86.4% (293/339) in group C1 and 92.3% (277/300) in group S1. Among adverse reactions (ARs) reported within 7 days of vaccination, the incidence was similarly high in both the co-administration and staggered vaccination groups (92.8% vs. 95.5%). INTERPRETATION: Our results demonstrated favorable safety and immunogenicity of co-administration of sIPV with other routine infant vaccines according to a 3-dose primary immunization schedule.

Humans↗

PubMed2026

Associations Between Routine Vaccinations and the Risk of New-Onset Idiopathic Uveitis.

OBJECTIVE: To evaluate the association between vaccination and the risk of new-onset idiopathic uveitis (NIU). DESIGN: Retrospective cohort study of aggregated electronic health records from multiple health systems across the United States. SUBJECTS: Subjects who received the coronavirus disease 2019 (COVID-19), human papillomavirus (HPV), varicella, recombinant herpes zoster, or live herpes zoster vaccinations from 2006 to 2025 and propensity-score matched controls. INTERVENTION: Vaccines against COVID-19, HPV, varicella, recombinant herpes zoster, or live herpes zoster. MAIN OUTCOMES AND MEASURES: The main outcome was the incidence of NIU at 3, 6, and 12 months following vaccination. Vaccinated patients were compared with matched controls who did not receive the respective vaccines. Analyses were repeated, excluding patients with previous diagnosis of the respective viral infection. Risk ratios (RR) with 95% confidence intervals (CIs) were calculated for overall NIU and constituent subtypes (anterior, intermediate, posterior, and panuveitis). RESULTS: All tested vaccinations were associated with reduced risk of NIU through 12 months compared with matched controls. Relative risk reductions were 65% for COVID-19 (RR, 0.35; CI, 0.33-0.37), 56% for HPV (RR, 0.44; CI, 0.35-0.54), 71% for varicella (RR, 0.29; CI, 0.25-0.33), 68% for live zoster (RR, 0.32; CI, 0.23-0.43), and 69% for recombinant zoster vaccination (RR, 0.31; CI, 0.26-0.37). Similar reductions were observed after excluding patients with prior diagnoses of the respective viral infections. CONCLUSIONS: Vaccination was associated with a lower risk of idiopathic uveitis, representing the complex interplay between immune modulation and the development of NIU.

Humans↗

PubMed2026

Do vaccinated cases transmit measles? A systematic review and meta-analysis.

INTRODUCTION: We reviewed evidence on whether vaccinated individuals can transmit measles and conducted a meta-analysis to understand transmission characteristics. METHODS: We searched and extracted data from peer-reviewed and gray literature and included studies reporting measles transmission events from vaccinated individuals. We meta-analyzed the data to calculate the median number of transmissions from vaccinated cases by measles burden, number of doses, and time since first and last dose. RESULTS: We identified 11,911 peer-reviewed and 22 gray literature records and included 33 articles in our review. Seventy individuals who had received 1 or more doses of measles-containing vaccine transmitted measles virus, resulting in 237 secondary cases. Vaccinated transmitters in eliminated areas were older (median age of 19 years (IQR: 3, 21)) than those in non-eliminated areas (median age 16 years; IQR 13, 18) (p = 0.12). Additionally, 91% (30/33) of studies provided data on subsequent transmission generations, leading to 812 measles cases traced back to vaccinated individuals, with a median of 4 (IQR: 1, 10) cases per vaccinated transmitter. CONCLUSION: Measles transmissions from vaccinated cases, although relatively uncommon, must be considered in public health investigations, as such transmissions can contribute to outbreaks.

Adolescent↗

PubMed2026

Immunogenicity of Two Versus Three Doses of Hepatitis B Vaccine When Administered to Children Aged 2-18 Months: A Randomized Clinical Trial.

BACKGROUND: A 2-dose hepatitis B vaccination schedule is highly immunogenic in children aged ≥1 year, but data for infants are scarce. Our goal was to compare the immunogenicity of 2- and 3-dose hepatitis B vaccination schedules in this population. METHODS: Children in the experimental group were recruited at 2 months of age and randomized to receive a homologous (Infanrix-hexa/Infanrix-hexa) or heterologous (Infanrix-hexa/Twinrix) 2-dose schedule at 2 and 12 months. Children in the control group were recruited at 18 months and had received a homologous 3-dose schedule (Infanrix-hexa/Infanrix-hexa/Infanrix-hexa) at 2, 4, and 18 months. All groups received a challenge dose (Twinrix) 3 years later. RESULTS: One month after the primary series, seroprotection rates (anti-HBs ≥10 mIU/mL) were high and similar among the 3 groups (heterologous 2-dose, 91.7%; homologous 2-dose, 90.9%; 3-dose, 94.2%). Geometric mean titers (GMTs) were lower in the 2-dose groups than in the 3-dose group. Post-challenge dose, the majority exhibited an anamnestic response, similar across all 3 groups (heterologous 2-dose, 97.2%; homologous 2-dose, 95.5%; 3-dose, 92.7%). GMTs were numerically higher in the heterologous 2-dose group (9380.5 mIU/mL) than in the 3-dose group (6900.6 mIU/mL) (P = .4). The proportion exhibiting local reactions was significantly lower after the heterologous 2-dose schedule than after the homologous 2-dose schedule. CONCLUSIONS: The anamnestic response 3 years after 2-dose (2 and 12 months) and 3-dose (2, 4, and 18 months) hepatitis B vaccination schedules was similar. The heterologous 2-dose schedule was more immunogenic and less reactogenic than the homologous 2-dose schedule.

Humans↗

PubMed2026

Maternal vaccination with RSVpreF and risk of hypertensive disorders of pregnancy: a systematic review and meta-analysis.

BACKGROUND: A bivalent respiratory syncytial virus (RSV) prefusion F protein-based vaccine (RSVpreF) was approved in the United States in August 2023 for use during pregnancy to prevent infant RSV-associated lower respiratory tract disease. The pivotal phase 3 trial identified a numerical imbalance in hypertensive disorders of pregnancy (HDP) that did not reach statistical significance; postmarketing observational studies have since reported inconsistent findings. We conducted a systematic review and meta-analysis to assess this association. METHODS: We searched MEDLINE, Embase, CENTRAL, Scopus, ClinicalTrials.gov, and WHO ICTRP from inception to Jan 26, 2026, for randomized controlled trials (RCTs) and observational studies comparing HDP outcomes in RSVpreF-vaccinated versus unvaccinated or placebo-receiving pregnant individuals. Unadjusted risk ratios (RRs) were pooled using a random-effects model; adjusted estimates from observational studies were pooled separately by inverse variance methods. This study is registered with PROSPERO (CRD420251026835). RESULTS: Nine studies were included (3 RCTs, 6 retrospective cohort studies; n = 148,267). RSVpreF vaccination was associated with a small but statistically significant increase in overall HDP risk (RR 1·08, 95% CI 1·02-1·13; p = 0·004; I2 = 44%), driven by the observational studies group (1·08, 1·02-1·14; I2 = 61%); RCTs showed a directionally consistent but non-significant RR (1·12, 0·87-1·43; I2 = 0%). The association was attributable to gestational hypertension, with no significant association for preeclampsia/eclampsia. CONCLUSION: Maternal RSVpreF vaccination was associated with a small increase in HDP attributable to gestational hypertension and driven primarily by observational studies, in which residual confounding remains possible. The benefits of infant RSV prevention remain substantial, and these findings support continued postmarketing surveillance and informed shared decision-making.

Humans↗

PubMed2026

Safety and Immunogenicity of Varicella Vaccination in Children and Adolescents Living With HIV: A Systematic Review.

INTRODUCTION: Preventing varicella-zoster virus infection is important in the management of human immunodeficiency virus (HIV)-positive persons. Varicella remains endemic worldwide, and HIV-positive persons can experience greater morbidity than the general population. We summarized the global literature on the safety and immunogenicity of the varicella vaccine in HIV-positive children. METHODS: Systematic review of original reports on varicella vaccination of HIV-positive children, published through December 31, 2024, including assessment of safety, immunologic responses and effectiveness after vaccination. RESULTS: Eighteen articles were analyzed. Local reactions were the most common adverse events, albeit infrequent (<21% and <10% of vaccinees after dose 1 and 2, respectively). Systemic reactions were also infrequent, consisting mostly of low-grade fever. A vaccine-related rash, reported in <5% of vaccinees, had fewer lesions and a shorter duration than typical varicella. Serious adverse events were reported only when the vaccine was inadvertently administered to children with severe HIV immunosuppression. Varicella vaccination had no clinically significant impact on plasma HIV RNA or CD4+ T-cell count after either dose. An antibody response was reported in 60%-79% of HIV-positive vaccinees after dose 2 and often declined more rapidly than in uninfected children. Cell-mediated immunity was detected in 67%-83% after dose 2. No significant differences in adverse events or short-term immune response after vaccination correlated with past or current CD4+ T-cell status. CONCLUSIONS: The varicella vaccine had a favorable safety profile and induced specific immune responses in most nonseverely immunocompromised HIV-positive children. The vaccine remains contraindicated for persons with severe HIV infection. Robust data on the durability of immune response and long-term effectiveness are needed.

Humans↗

PubMed2026

Immunogenicity and safety of prophylactic HPV vaccines in people living with HIV: A systematic review and meta-analysis.

Human papillomavirus (HPV) is a major global public health concern, causing genital warts and cancers of the cervix, anus, oropharynx, vulva, and penis. People living with HIV (PLWH) face a disproportionately elevated burden of HPV infection and HPV-related malignancies due to chronic immunosuppression. We conducted a systematic review and meta-analysis searching six databases from January 2006 to June 2026 without language restrictions. Twenty-five studies were included in the systematic review; 12 independent studies (N = 1,493 for HPV16) were included in the quantitative meta-analysis. Using a DerSimonian-Laird random-effects model with logit transformation, pooled seroconversion rates were: HPV16 97.8% (95% CI: 94.9-99.1%; I2 = 89.6%; 15 datasets), HPV18 94.2% (95% CI: 86.1-97.7%; I2 = 95.8%; 13 datasets), HPV6 97.0% (95% CI: 93.7-98.6%; I2 = 66.1%; 10 studies), and HPV11 97.1% (95% CI: 90.5-99.1%; I2 = 95.5%; 10 studies). CD4 count was the most consistently reported modifier of immunogenic response: HPV16 seroconversion was 98.5% in PLWH with CD4 > 350 cells/μL vs. 71.1% in those with CD4 ≤ 200 cells/μL (ACTG A5240). All three vaccine generations demonstrated high immunogenicity. Two doses of the nonavalent vaccine were non-inferior to three doses in virologically suppressed women (Papillon RCT). No vaccine-related serious adverse events were reported. GRADE certainty of evidence was moderate for HPV16, HPV6, and HPV11, and low for HPV18. Prophylactic HPV vaccination achieves high seroconversion rates across all vaccine generations in PLWH. CD4 count significantly modifies vaccine response, underscoring the importance of vaccination before severe immunosuppression develops. These findings support current international recommendations advocating HPV vaccination for all PLWH.

Humans↗

PubMed2026

Immunogenicity and safety of inactivated TZ84- vs. HM175-based hepatitis A vaccines in pediatric populations: A systematic review and meta-analysis.

Individual studies indicate stronger and persistent long-term immunogenicity with TZ84-based than HM175-based hepatitis A vaccines. This systematic review and meta-analysis compared immunogenicity and safety of inactivated TZ84- and HM175-based hepatitis A vaccines in children and adolescents. Studies involving adults, immunocompromised populations, non-comparative designs, non-English publications, and studies with non-extractable outcomes were excluded. MEDLINE/PubMed, Google Scholar, other electronic databases, and grey literature were searched (September-October 2025). Risk of bias was assessed using the Cochrane Risk of Bias 2 (RoB 2) tool, and meta-analyses were performed where appropriate. Seven publications arising from four randomized cohorts (total participants: 3,282) reporting seroconversion rates (SCRs), geometric mean concentrations (GMCs), long-term seroprotection, and adverse events (AEs) were identified. Pooled analyses demonstrated higher SCRs and GMCs with TZ84 than HM175-based vaccines following both one and two doses. SCRs at 1 month [odds ratio (OR): 3.05; 95% confidence interval (CI): 1.88-4.96] and GMCs at 7 months [standardized mean difference (SMD): 0.88; 95% CI: 0.18-1.58; p = .01] both favored TZ84-based vaccines. Long-term follow-up (up to 186 months/15.5 y) showed higher reported anti-HAV antibody concentrations for TZ84-based vaccines. The AEs were comparable between vaccine types (RR: 0.95; 95% CI: 0.76-1.20; p = .69). Evidence was limited by the small number of unique randomized cohorts, geographic concentration in China, heterogeneity across studies, and reliance on surrogate immunogenicity outcomes. Overall, available evidence suggests that TZ84-based hepatitis A vaccines (HAPIBEV™/HEALIVE®) are associated with higher reported antibody responses and greater reported antibody persistence than the HM175-based vaccine (HAVRIX®) in children and adolescents, with comparable safety profiles.Registration: PROSPERO CRD420251154480.

Humans↗

PubMed2026

Pre-clinical immunogenicity and safety evaluation of H2 strain Hepatitis A Inactivated Vaccine in rhesus macaques.

BACKGROUND: Hepatitis A is a viral infection of the liver that can cause mild to severe illness. Currently, two types of HAV vaccines are used worldwide, inactivated hepatitis A vaccines, which are used in most countries, and live attenuated vaccines (H2 and L-A-1 strain), which are mainly used in China. The major disadvantage of live attenuated virus to cause secondary infections among contacts and mutation shifts of the live vaccine strain. The H2 strain was selected for the development of an inactivated hepatitis A vaccine to further reduce biosafety risks. Rhesus macaques high genomic homology with humans and the incubation period after hepatitis A vaccination and human natural infections are similar. We use rhesus macaques to assess immunogenicity and safety of the H2 strain Hepatitis A Inactivated Vaccine. METHODS: The vaccine was assessed in rhesus macaques, divided into four groups (n = 10 per group): the control group (adjuvant buffer; aluminum content 0.35 mg/mL; 2 mL per dose), the low-dose group (320EU, 0.5 mL of 640EU/mL with aluminum content 0.35 mg/mL), the medium-dose group (640EU, 1 mL of 640EU/mL with aluminum content 0.35 mg/mL), and the high-dose group (1280EU, 2 mL of 640EU/mL with aluminum content 0.35 mg/mL). Animals were injected intramuscularly at multiple sites in the hind limbs and received four inoculations at 4-week intervals. Test items including Clinical indicators, immunogenicity indicators and Histopathological examination. RESULTS: No abnormalities were observed in any group in terms of general clinical condition throughout the study period except for slight decreases in body temperature after immunization. Hematological parameters, serum biochemistry indices, and histopathological findings showed fluctuated to different degrees of fluctuation after immunization across all groups. Immunogenicity assessments showed that the inactivated hepatitis A vaccine (H2) induced both humoral and cellular immune responses effectively, and the levels of antibodies increased with certain dose- and time-response trends. CONCLUSION: The inactivated hepatitis A vaccine (H2 strain, human diploid cell) was safe and immunogenic in non-human primates. The results provide strong preclinical support for the further clinical development of this vaccine candidate.

Animals↗