Long Term Protective Immunity to Goatpox in Goats After Single Immunization with a Live Attenuated Goatpox Vaccine

In this study, duration of immunity following single shot vaccination using an attenuated goatpox vaccine (GTPV/Uttarkashi/1978) was evaluated in sero-negative kids for 52 months. Long term immunity was evaluated by clinical protection upon virulent virus challenge and serum neutralization assay applied for serum samples. Rise in level of GTPV specific antibodies was found to be maximum on 21 days post vaccination, which was maintained between 1 and 2 years of immunization with steady decline. Upon virulent virus challenge on 21 days, 12, 24, 42 and 52 months post vaccination, protection in all vaccinated animals was evident, whereas, control animals developed severe clinical disease. This is for the first time that long term immunity of a live goatpox vaccine has been investigated up to 52 months of post-vaccination in goats and it has immense potential in controlling and eradicating goatpox from an enzootic situation.

Children develop robust and sustained cross-reactive spike-specific immune responses to SARS-CoV-2 infection

SARS-CoV-2 infection is generally mild or asymptomatic in children but a biological basis for this outcome is unclear. Here we compare antibody and cellular immunity in children (aged 3–11 years) and adults. Antibody responses against spike protein were high in children and seroconversion boosted responses against seasonal Beta-coronaviruses through cross-recognition of the S2 domain. Neutralization of viral variants was comparable between children and adults. Spike-specific T cell responses were more than twice as high in children and were also detected in many seronegative children, indicating pre-existing cross-reactive responses to seasonal coronaviruses. Importantly, children retained antibody and cellular responses 6 months after infection, whereas relative waning occurred in adults. Spike-specific responses were also broadly stable beyond 12 months. Therefore, children generate robust, cross-reactive and sustained immune responses to SARS-CoV-2 with focused specificity for the spike protein. These findings provide insight into the relative clinical protection that occurs in most children and might help to guide the design of pediatric vaccination regimens.

Third COVID-19 Vaccine Dose Boosts Neutralising Antibodies in Poor Responders

ABSTRACTObjectiveTo determine if poor responders to COVID-19 RNA vaccines (<50% neutralisation) after two doses would remain poor responders, or if a third dose could elicit high levels of NAbs.DesignClinical follow-up studySettingAcademic and medical institutions in USAParticipants269 healthy individuals ranging in age from 19 to 80 (Average age = 51; 165 females and 104 males) who received either BNT162b2 (Pfizer) or mRNA1273 (Moderna) vaccines.Main Outcome MeasuresNAb levels were measured: i) 2-4 weeks after a second vaccine dose, ii) 2-4 months after the second dose, iii) within 1-2 weeks prior to a third dose and iv) 2-4 weeks after a third RNA vaccine dose.ResultsIn 269 study participants, percent neutralisation ranged from 0% to 99% 2-4 weeks after a second vaccine dose. The majority of vaccine recipients (154/269, 57%) demonstrated NAb levels at ≥75% 2-4 weeks after their second dose. Our study also revealed that 25% of vaccine recipients did not neutralise above 50% (Median neutralisation = 21%, titers <1:80) within a month after their second dose. We called these individuals “vaccine poor responders” (VPRs). Twenty-three VPRs ranging in age from 31 to 79 (10 males, 13 females, average age = 62.5) independently obtained a third dose of either BNT162b2 or mRNA-1273 vaccine 1-8 months (average = 5 months) after their second dose. Within a month after their third dose, poor responders showed an average 20-fold increase in NAb levels (range 46%-99%).ConclusionsThe results suggest that poor responders are not permanently poor responders; they can generate high NAb levels with an additional vaccine dose–independent of mRNA vaccine manufacturer. Previous reports indicate that NAb levels decline much more rapidly than clinical protection from hospitalisation and disease, but that does not account for vaccine recipients who never generated high levels of NAbs after two doses. It is possible that poor responders are a source of breakthrough infections. Although it is not known what levels of NAbs protect from infection or disease, many vaccine recipients in high-risk professions may wish to keep peripheral NAb levels high, limiting infection, asymptomatic viral replication, and potential transmission.

Clinical Phenotype and Contagiousness of Early Breakthrough SARS-CoV-2 Infections after BNT162b2 COVID-19 mRNA Vaccine: A Parallel Cohort Study in Healthcare Workers

We evaluated the clinical protection of BNT162b2 mRNA vaccine in healthcare workers (HCWs) and how COVID-19 manifestations and contagiousness change as the time since first dose increases. A matched (1:2 ratio) parallel cohort study was performed. During the first three months of vaccination campaign, HCWs of the entire health district ASL Città di Torino (Turin, Italy) were classified according to SARS-CoV-2-positivity in respect of the vaccination schedule: post-first-dose (fHCWs, <12 days), partially (PHCWs, ≥12 from first dose to ≤7 days after the second), and totally vaccinated (THCWs, ≥8 days after the second dose). Age-/sex-matched unvaccinated controls were randomly selected from all the SARS-CoV-2-positivity detected in the same district and period. Previous infections were excluded. Clinical and virologic data (ORF1ab gene cycle threshold values, Ct) were recorded. In total, 6800 HCWs received at least one dose, and 55 tested positive subsequently: 20 fHCWs, 25 PHCWs, 10 THCWs. Furthermore, 21.8% of breakthrough infections were in male, with a median age of 49 years (32–56), and 51.4% occurred while SARS-CoV-2 B.1.1.7 variant was predominant. The incident relative risk was 0.13 (0.12–0.15) for PHCWs and 0.06 (0.05–0.07) for THCWs. Compared to controls (n = 110), no difference was observed in fHCWs, while PHCWs and THCWs showed higher prevalence of asymptomatic infections, fewer signs/symptoms with a milder systemic involvement, and significantly higher Ct values (PHCWs 30.3 (24.1–35.5) vs. 22.3 (19.6–30.6), p = 0.023; THCWs 35.0 (31.3–35.9) vs. 22.5 (18.2–30.6), p = 0.024). Duration of symptoms was also shorter in THCWs (5 days (3–6) vs. 9 (7–14), p = 0.028). A linear increase of 3.81 points in Ct values was observed across the groups by vaccination status (p = 0.001) after adjusting for age, sex, comorbidities, and time between COVID-19 onset and swab collection. BNT162b2 decreased the risk of PCR-confirmed infections and severe disease, and was associated with a virologic picture of lesser epidemiologic concern as soon as 12 days after the first vaccine dose.

Simultaneous Infection With Porcine Reproductive and Respiratory Syndrome and Influenza Viruses Abrogates Clinical Protection Induced by Live Attenuated Porcine Reproductive and Respiratory Syndrome Vaccination

The porcine respiratory disease complex (PRDC) is responsible for significant economic losses in the pig industry worldwide. Porcine reproductive and respiratory syndrome virus (PRRSV) and swine influenza virus are major viral contributors to PRDC. Vaccines are cost-effective measures for controlling PRRS, however, their efficacy in the context of co-infections has been poorly investigated. In this study, we aimed to determine the effect of PRRSV-2 and swine influenza H3N2 virus co-infection on the efficacy of PRRSV modified live virus (MLV) vaccination, which is widely used in the field. Following simultaneous challenge with contemporary PRRSV-2 and H3N2 field isolates, we found that the protective effect of PRRS MLV vaccination on clinical disease and pathology was abrogated, although viral load was unaffected and antibody responses were enhanced. In contrast, co-infection in non-immunized animals reduced PRRSV-2 viremia and H3N2 virus load in the upper respiratory tract and potentiated T cell responses against both PRRSV-2 and H3N2 in the lung. Further analysis suggested that an upregulation of inhibitory cytokines gene expression in the lungs of vaccinated pigs may have influenced responses to H3N2 and PRRSV-2. These findings provide important insights into the effect of viral co-infections on PRRS vaccine efficacy that may help identify more effective vaccination strategies against PRDC in the field.

Immunogenicity of a third scheduled dose of rotavirus vaccine in Australian Indigenous infants to improve protection against gastroenteritis: a phase IV, double-blind, randomised, placebo-controlled clinical trial

BackgroundThe oral rotavirus vaccine, Rotarix (GlaxoSmithKline), is licensed for use in infants as two doses in the first six months of life. For infants living in settings with high child-mortality, and also for rural and remote Australian Aboriginal infants, clinical protection conferred by two doses of Rotarix appears to be reduced. We assessed the effect of an additional dose of Rotarix on vaccine immune responses among Aboriginal children who are 6 to < 12 months old.MethodsORVAC is a two-stage, double-blind, randomised, placebo-controlled trial conducted across regional urban and remote locations of Australia’s Northern Territory. Aboriginal children 6 to < 12 months old who had received one or two prior doses of Rotarix were randomised 1:1 to receive an additional dose of Rotarix or matched placebo. The primary immunological endpoint was seroresponse defined as an anti-rotavirus IgA level ≥ 20 AU/mL, approximately one month following Rotarix or placebo. ClinicalTrials.gov (NCT02941107).FindingsBetween March 2018 and August 2020, 253 infants were enrolled. Of these, 178 infants (70%) had analysable serological results after follow-up; 89 randomised to Rotarix and 89 to placebo. The proportion with a seroresponse was 85% after Rotarix compared to 71% after placebo; the probability of a higher rate of seroresponse in the Rotarix than the placebo arm was 99%. There were no occurrences of intussusception or any serious adverse events attributed to Rotarix or placebo in the 28 days following the additional dose of Rotarix or placebo.InterpretationAn additional dose of Rotarix among Australian Aboriginal infants 6 to < 12 months old increased the proportion with a vaccine seroresponse. If it can be proven that this translates into better protection against disease, scheduling an additional dose may be a viable strategy for further reducing the global burden of rotavirus disease.FundingNHMRC (GNT1086952).Research in contextEvidence before this studyRotavirus vaccine programs have reduced the global burden of gastroenteritis disease among young children, but rotavirus still causes >200,000 child deaths each year. A recent systematic review in the Lancet Global Health found that the effectiveness of oral rotavirus vaccines is variable, from 45 – 58% in settings with high child mortality to 83%-85% in settings with low child mortality. In high child mortality settings there is also evidence of waning effectiveness after 12 months old. Reduced vaccine effectiveness has also been reported among Australian Aboriginal children. Previous trials have failed to demonstrate improved rotavirus vaccine effectiveness with strategies such as withholding breastfeeding, or co-administering vaccines with probiotics or zinc. Pre-licensure studies of Rotarix in Africa did not clearly indicate whether a three-dose Rotarix schedule had benefit over a two-dose schedule, although all vaccine doses were given before infants were six months old when maternal antibodies may impede vaccine responses. Trials in Bangladesh and Mali found that a third Rotarix dose given after 6 months old improved the immune response to vaccine.Added value of this studyIn the first stage of our novel two-stage randomised clinical trial, we showed that scheduling an additional Rotarix dose for remote Australian Aboriginal infants after 6 months old increased the proportion with evidence of vaccine seroresponse.Implications of all the available evidenceScheduling an additional dose of Rotarix after 6 months old is feasible, and trials in three settings have now demonstrated that it improves immune responses. Trials should now be conducted in a number of high burden settings to determine whether this strategy results in improved clinical protection against severe gastroenteritis.

Association between hemagglutination inhibition antibody titers and protection against RT-PCR confirmed influenza illness in children 6−35 months of age: statistical evaluation of a correlate of protection

Background Data from a randomized, controlled efficacy trial of an inactivated quadrivalent influenza vaccine in children 6−35 months of age were used to determine whether hemagglutination inhibition (HI) antibody titer against A/H1N1 and A/H3N2 is a statistical correlate of protection (CoP) for the risk of RT-PCR-confirmed influenza associated with the corresponding strain. Methods The Prentice criteria were used to statistically validate strain-specific HI antibody titer as a CoP. The probability of protection was identified using Dunning's model corresponding to a pre-specified probability of protection at an individual level. The group level protective threshold was identified using Siber's approach, leading to unbiased predicted vaccine efficacy (VE). A case-cohort sub-sample was used for this exploratory analysis. Results Prentice criteria confirmed that HI titer is a statistical CoP for RT-PCR-confirmed influenza. Dunning's model predicted a probability of protection of 49.7% against A/H1N1 influenza and 54.7% against A/H3N2 influenza at an HI antibody titer of 1:40 for the corresponding strain. Higher titers of 1:320 were associated with more than 80% probability of protection. Siber's method predicted VE of 61.0% at a threshold of 1:80 for A/H1N1 and 46.6% at 1:113 for A/H3N2. Conclusions The study validated HI antibody titer as a statistical CoP, by demonstrating that HI titer is correlated with clinical protection against RT-PCR-confirmed influenza associated with the corresponding influenza strain and is predictive of VE in children 6−35 months of age.

Individual-level variations in malaria susceptibility and acquisition of clinical protection

After decades of research, our understanding of when and why individuals infected with Plasmodium falciparum develop clinical malaria is still limited. Correlates of immune protection are often sought through prospective cohort studies, where measured host factors are correlated against the incidence of clinical disease over a set period of time. However, robustly inferring individual-level protection from these population-level findings has proved difficult due to small effect sizes and high levels of variance underlying such data. In order to better understand the nature of these inter-individual variations, we analysed the long-term malaria epidemiology of children ≤12 years old growing up under seasonal exposure to the parasite in the sub-location of Junju, Kenya. Despite the cohort’s limited geographic expanse (ca. 3km x 10km), our data reveal a high degree of spatial and temporal variability in malaria prevalence and incidence rates, causing individuals to experience varying levels of exposure to the parasite at different times during their life. Analysing individual-level infection histories further reveal an unexpectedly high variability in the rate at which children experience clinical malaria episodes. Besides exposure to the parasite, measured as disease prevalence in the surrounding area, we find that the birth time of year has an independent effect on the individual’s risk of experiencing a clinical episode. Furthermore, our analyses reveal that those children with a history of an above average number of episodes are more likely to experience further episodes during the upcoming transmission season. These findings are indicative of phenotypic differences in the rates by which children acquire clinical protection to malaria and offer important insights into the natural variability underlying malaria epidemiology.

Durability of antibody response to vaccination and surrogate neutralization of emerging variants based on SARS-CoV-2 exposure history

Two-dose messenger RNA vaccines against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are highly effective in preventing symptomatic COVID-19 infection. However, the durability of protection is not known, nor is the effectiveness against emerging viral variants. Additionally, vaccine responses may differ based on prior SARS-CoV-2 exposure history. To investigate protection against SARS-CoV-2 variants we measured binding and neutralizing antibody responses following both vaccine doses. We document significant declines in antibody levels three months post-vaccination, and reduced neutralization of emerging variants, highlighting the need to identify correlates of clinical protection to inform the timing of and indications for booster vaccination.

Duration of Protective Immunity in Sheep Vaccinated with a Combined Vaccine against Peste des Petits Ruminants and Sheep Pox

In this study, the ability of the combined vaccine against peste des petits ruminants (PPR) (Nigeria strain 75/1) and sheep pox (SPP) (NISKhI strain) to form a protective immune response for 12 months in Kazakh breed fine-fleeced sheep aged 6–12 months was demonstrated. The duration of the protective immunity of immunized sheep from PPR and from SPP was evaluated using a serum neutralization test (SNT), followed by testing of the resistance of vaccinated sheep to infection with the field strain Kentau-7 of the PPRV and the virulent strain A of the SPPV. The PPR antibody response was additionally measured by c-ELISA. A single immunization of sheep with a combined vaccine in a volume of 2.0 mL, containing the PPR and SPP vaccine viruses in the titers of 103.0 TCID50/mL, provided reliable protection of animals from two infections simultaneously for 12 months (observation period). At the same time, in sheep immunized with the combined vaccine, antibodies of PPRV persisted for up to 12 months, with slight fluctuations. The combined vaccine induced 100% clinical protection against the field strain of PPRV and the virulent strain of SPPV in immunized sheep for up to 12 months, while unvaccinated animals became ill with the manifestation of clinical signs specific to PPRV and SPPV.