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Most COVID-19 vaccines are designed to elicit immune responses, ideally neutralizing antibodies (NAbs), against the SARS-CoV-2 spike protein. Several vaccines, including mRNA, adenoviral-vectored, protein subunit and whole-cell inactivated virus vaccines, have now reported efficacy in phase III trials and have received emergency approval in many countries. The two mRNA vaccines approved to date show efficacy even after only one dose, when non-NAbs and moderate T helper 1 cell responses are detectable, but almost no NAbs. After a single dose, the adenovirus vaccines elicit polyfunctional antibodies that are capable of mediating virus neutralization and of driving other antibody-dependent effector functions, as well as potent T cell responses. These data suggest that protection may require low levels of NAbs and might involve other immune effector mechanisms including non-NAbs, T cells and innate immune mechanisms. Identifying the mechanisms of protection as well as correlates of protection is crucially important to inform further vaccine development and guide the use of licensed COVID-19 vaccines worldwide.This Progress article summarizes our current understanding of the immune mechanisms of protection induced by the available COVID-19 vaccines. The authors compare vaccine-induced antibody responses following one or two doses of different vaccines and consider the relative importance of neutralizing antibodies for vaccine-mediated protection against SARS-CoV-2.

The encapsulated bacteria , and (Group B Streptococcus) have been responsible for the majority of severe infections in children for decades, specifically bacteremia and meningitis. Isolates which cause invasive disease are usually surrounded by a polysaccharide capsule, which is a major virulence factor and the key antigen in protective protein-polysaccharide conjugate vaccines. Protection against these bacteria is largely mediated via polysaccharide-specific antibody and complement, although the contribution of these and other components, and the precise mechanisms, vary between species and include opsonophagocytosis and complement-dependent bacteriolysis. Further studies are required to more precisely elucidate mechanisms of protection against non-type b and Group B Streptococcus.

The risk and severity of specific infections are increased during pregnancy due to a combination of physiological and immunological changes. Characterizing the maternal immune system during pregnancy is important to understand how the maternal immune system maintains tolerance towards the allogeneic fetus. This may also inform strategies to prevent maternal fatalities due to infections and optimize maternal vaccination to best protect the mother-fetus dyad and the infant after birth. In this review, we describe what is known about the immunological changes that occur during a normal pregnancy.

The mammalian intestinal tract harbors a diverse community of trillions of microorganisms, which have co-evolved with the host immune system for millions of years. Many of these microorganisms perform functions critical for host physiology, but the host must remain vigilant to control the microbial community so that the symbiotic nature of the relationship is maintained. To facilitate homeostasis, the immune system ensures that the diverse microbial load is tolerated and anatomically contained, while remaining responsive to microbial breaches and invasion. Although the microbiota is required for intestinal immune development, immune responses also regulate the structure and composition of the intestinal microbiota. Here we discuss recent advances in our understanding of these complex interactions and their implications for human health and disease.

A correlate of protection (CoP) is an immunological marker associated with protection against infection. Despite an urgent need, a CoP for SARS-CoV-2 is currently undefined. Our objective was to review the evidence for a humoral correlate of protection for SARS-CoV-2, including variants of concern. We searched OVID MEDLINE, EMBASE, Global Health, Biosis Previews and Scopus to January 4, 2022 and pre-prints (using NIH iSearch COVID-19 portfolio) to December 31, 2021, for studies describing SARS-CoV-2 re-infection or breakthrough infection with associated antibody measures. Two reviewers independently extracted study data and performed quality assessment. Twenty-five studies were included in our systematic review. Two studies examined the correlation of antibody levels to VE, and reported values from 48.5% to 94.2%. Similarly, several studies found an inverse relationship between antibody levels and infection incidence, risk, or viral load, suggesting that both humoral immunity and other immune components contribute to protection. However, individual level data suggest infection can still occur in the presence of high levels of antibodies. Two studies estimated a quantitative CoP: for Ancestral SARS-CoV-2, these included 154 (95% confidence interval (CI) 42, 559) anti-S binding antibody units/mL (BAU/mL), and 28.6% (95% CI 19.2, 29.2%) of the mean convalescent antibody level following infection. One study reported a CoP for the Alpha (B.1.1.7) variant of concern of 171 (95% CI 57, 519) BAU/mL. No studies have yet reported an Omicron-specific CoP. Our review suggests that a SARS-CoV-2 CoP is likely relative, where higher antibody levels decrease the risk of infection, but do not eliminate it completely. More work is urgently needed in this area to establish a SARS-CoV-2 CoP and guide policy as the pandemic continues.

Bacterial meningitis is a devastating infection, with a case fatality rate of up to 30% and 50% of survivors developing neurological complications. These include short-term complications such as focal neurological deficit and subdural effusion, and long-term complications such as hearing loss, seizures, cognitive impairment and hydrocephalus. Complications develop due to bacterial toxin release and the host immune response, which lead to neuronal damage. Factors associated with increased risk of developing neurological complications include young age, delayed presentation and Streptococcus pneumoniae as an etiologic agent. Vaccination is the primary method of preventing bacterial meningitis and therefore its complications. There are three vaccine preventable causes: Haemophilus influenzae type b (Hib), S. pneumoniae, and Neisseria meningitidis. Starting antibiotics without delay is also critical to reduce the risk of neurological complications. Additionally, early adjuvant corticosteroid use in Hib meningitis reduces the risk of hearing loss and severe neurological complications.

Infection with Haemophilus influenzae, Neisseria meningitidis, and Streptococcus pneumoniae causes substantial mortality and long-term morbidity in children. We know of no study to assess the long-term trends in hospital admission rates for meningitis and septicaemia caused by these pathogens in children in England. We aimed to do such a study using routinely reported data in England. In this population-based observational study, we used datasets that include routinely collected administrative statistics for hospital care: the Hospital In-Patient Enquiry (data for England from 1968 to 1985), the Hospital Episode Statistics dataset (data for England from 1989 onwards), and the Oxford record linkage study (data for Oxfordshire and surrounding areas from 1963 to 2011). We analysed annual age-specific and age-standardised admission rates in children younger than 15 years with H influenzae, meningococcal and pneumococcal meningitis, and septicaemia. We saw a reduction in hospital admission rates for childhood invasive bacterial disease after the introduction of conjugate vaccines against H influenzae, N meningitidis, and S pneumoniae in England. Annual incidence of H influenzae meningitis per 100 000 children decreased from 6·72 admissions (95% CI 6·18–7·26) in 1992 to 0·39 admissions (0·26–0·52) in 1994, after the introduction of routine H influenzae type b vaccination. We saw a small rise in admissions in the early 2000s, peaking at 1·24 admissions per 100 000 children (0·99–1·48) in 2003, which decreased to 0·28 per 100 000 children (0·17–0·39) by 2008 after the introduction of catch-up (2003) and routine (2006) booster programmes for young children. Meningococcal disease increased during the 1990s, reaching a peak in 1999, with 34·54 admissions (33·30–35·78) per 100 000 children. Hospital admissions decreased after the meningococcal serogroup C vaccine was introduced in 1999 and was 12·40 admissions (11·68–13·12) per 100 000 in 2011. Admissions for invasive pneumococcal disease increased from the 1990s reaching a peak in 2006 at 4·45 admissions for meningitis (95% CI 4·0–4·9) per 100 000 children and 2·81 admissions for septicaemia (2·45–3·17) per 100 000 children. A reduction in admissions occurred after the introduction of the pneumococcal conjugate vaccine in 2006: hospital admission rates in 2011 were 2·03 per 100 000 children for meningitis and 1·12 per 100 000 children for septicaemia. Vaccine-preventable invasive bacterial disease in children has decreased substantially in England in the past five decades, most notably with the advent of effective conjugate vaccines since the 1990s. Ongoing disease surveillance and continued development and implementation of vaccines against additional pneumococcal serotypes and serogroup B meningococcal disease are important. None.

Human parechovirus infections are the second most common cause of viral meningitis in children. These infections are most frequently seen in infants younger than 90 days. Clinical manifestations include encephalitis, meningitis, myocarditis, and sepsis, which can lead to serious neurodevelopmental sequelae in young infants. Molecular techniques, including PCR assays, are the preferred diagnostic methods and have contributed to an increase in reported cases, along with an increasing awareness of the causal role of human parechovirus in infant diseases. However, focused clinical and diagnostic investigations of human parechovirus in infants and the use of their results in management is varied, partly because of the scarcity of robust incidence data and spectrum of clinical presentations of the infection. In this Review, we outline clinical cohort and epidemiological studies that can be used to inform the evidence-based management of young infants with human parechovirus disease and identify key research priorities. An improved understanding of the pathogenesis and epidemiology of these infections is required to inform an evidence-based approach to diagnosis and treatment in the future.

A substantial reduction in bacterial meningitis has occurred in the UK following successful implementation of immunisation programmes. Most childhood meningitis in developed countries is now caused by viruses. Long-term trends in paediatric viral meningitis in England have not previously been reported. The objective of this study is to report on epidemiological trends over time in childhood viral meningitis in England. In this population-based observational study, we used routinely collected hospital discharge records from English National Health Service hospitals from 1968–2011 to analyse annual age-specific admission rates for viral meningitis, including specific viral aetiologies, in children younger than 15 years. We analysed hospital discharge records from Jan 1, 1968, to Dec 31, 2011. Hospital admission rates for viral meningitis from Jan 1, 1968, to Dec 31, 1985, varied annually, with a mean of 13·5 admissions per 100 000 children aged less than 15 years, per year (95% CI 13·0–14·0). Admission rates declined during the late 1980s, and the mean number of admissions from 1989–2011 was 5·2 per 100 000 per year (5·1–5·3). This decrease was entirely in children aged 1–14 years. Admission rates for infants aged less than 1 year increased since 2005, to 70·0 per 100 000 (63·7–76·2) in 2011, which was driven by an increase in admission of infants aged 90 days or less. In 1968–85, the majority of cases in children were in those aged 1–14 years (22 150 [89%] of 24 920 admissions). In 2007–11, 1716 (72%) of 2382 cases were in infants. Admissions for mumps-related meningitis almost disappeared following introduction of the measles-mumps-rubella (MMR) vaccine in 1988. Admissions with a specified viral aetiology have increased since 2000. Trends in viral meningitis admissions have changed substantially over the past 50 years, and probably reflect the impact of the MMR vaccine programme and the use of more sensitive diagnostic techniques. None.