Characterization and immunogenicity of a candidate subunit vaccine against varicella-zoster virus

Vaccines for post-exposure prophylaxis against varicella (chickenpox) in children and adults

BACKGROUND

The prevention of varicella (chickenpox) using live attenuated varicella vaccines has been demonstrated both in randomised controlled trials (RCTs) and in population-based immunisation programmes in countries such as the United States and Australia. Many countries do not routinely immunise children against varicella and exposures continue to occur. Although the disease is often mild, complications such as secondary bacterial infection, pneumonitis and encephalitis occur in about 1% of cases, usually leading to hospitalisation. The use of varicella vaccine in persons who have recently been exposed to the varicella zoster virus has been studied as a form of post-exposure prophylaxis (PEP).

OBJECTIVES

To assess the efficacy and safety of vaccines for use as PEP for the prevention of varicella in children and adults.

SEARCH METHODS

We searched CENTRAL (2014, Issue 1), MEDLINE (1966 to March week 1, 2014), EMBASE (January 1990 to March 2014) and LILACS (1982 to March 2014). We searched for unpublished trials registered on the clinicaltrials.gov and WHO ICTRP websites.

SELECTION CRITERIA

RCTs and quasi-RCTs of varicella vaccine for PEP compared with placebo or no intervention. The outcome measures were efficacy in prevention of clinical cases and/or laboratory-confirmed clinical cases and adverse events following vaccination.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted and analysed data using Review Manager software.

MAIN RESULTS

We identified three trials involving 110 healthy children who were siblings of household contacts. The included trials varied in study quality, vaccine used, length of follow-up and outcomes measured and, as such, were not suitable for meta-analysis. We identified high or unclear risk of bias in two of the three included studies. Overall, 13 out of 56 vaccine recipients (23%) developed varicella compared with 42 out of 54 placebo (or no vaccine) recipients (78%). Of the vaccine recipients who developed varicella, the majority only had mild disease (with fewer than 50 skin lesions). In the three trials, most participants received PEP within three days following exposure; too few participants were vaccinated four to five days post-exposure to ascertain the efficacy of vaccine given more than three days after exposure. No included trial reported on adverse events following immunisation.

AUTHORS' CONCLUSIONS

These small trials suggest varicella vaccine administered within three days to children following household contact with a varicella case reduces infection rates and severity of cases. We identified no RCTs for adolescents or adults. Safety was not adequately addressed.

Vaccines for post-exposure prophylaxis against varicella (chickenpox) in children and adults

BACKGROUND

Live attenuated varicella vaccines for the prevention of varicella (chickenpox) has been demonstrated both in randomised controlled trials (RCTs) and in population-based immunisation programmes in countries such as the United States. However, many countries do not routinely immunise children against varicella, and exposures continue to occur. Although the disease is often mild, complications such as secondary bacterial infection, pneumonitis and encephalitis occur in about 1% of cases, usually leading to hospitalisation. The use of varicella vaccine in persons who have recently been exposed to the varicella zoster virus has been studied as a form of post-exposure prophylaxis (PEP).

OBJECTIVES

To assess the efficacy and safety of vaccines for use as PEP for the prevention of varicella in children and adults.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library, 2008, Issue 1); MEDLINE (1966 to February 2008); and EMBASE (January 1990 to February 2008).

SELECTION CRITERIA

RCTs and quasi-RCTs of varicella vaccine for PEP compared with placebo or no intervention. The outcome measures were efficacy in prevention of clinical cases and/or laboratory-confirmed clinical cases and adverse effects following vaccination.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted and analysed data using Review Manager software.

MAIN RESULTS

Three studies involving 110 healthy children who were siblings of household contacts were identified as suitable for inclusion. The studies varied in quality, study design, vaccine used, and outcomes measured and, as such, were not suitable for meta-analysis. Overall, 13 out of 56 vaccine recipients (18%) developed varicella compared with 42 out of 54 placebo (or no vaccine) recipients (78%). Of the vaccine recipients who developed varicella, the majority only had mild disease (with less than 50 skin lesions). In the three studies, most subjects received PEP within three days following exposure; too few subjects were vaccinated four to five days post exposure to ascertain the efficacy of vaccine given more than three days after exposure. No included studies reported on adverse events following immunisation.

AUTHORS' CONCLUSIONS

These small trials suggest varicella vaccine administered within three days to children following household contact with a varicella case reduces infection rates and severity of cases. No RCTs for adolescents or adults were identified. However safety was not adequately addressed.

Humoral immunoresponse to varicella-zoster virus pernasally coadministered with Escherichia coli enterotoxin in mice

It is evaluated whether Escherichia coli enterotoxin is useful for induction of immunity to varicella-zoster virus (VZV) as a mucosal adjuvant in mice. When a commercially available live varicella vaccine (Oka strain) and toxin were administered simultaneously via a nasal route three times at 2 or 6 month intervals, an antibody neutralizing VZV was detected in half or all of the mice vaccinated, respectively. The antibody specific to the vaccine strain of VZV reacted to five proteins, molecular weights of which were 110 K, 100 K, 62 K, 54 K and 46 K. These proteins were composed of glycosylated products of all kinds of glycoproteins. These results suggest that although a nasal administration of the vaccine without the adjuvant has little immunogenicity in mice, the simultaneous administration of the live vaccine and the toxin over a long period induces a specific humoral immunity to VZV.

Assays for antibodies to varicella-zoster virus

Anti-varicella-zoster virus serum antibody assays and their use in vaccine development are described. Of particular interest are FAMA and neutralization assays and the gpELISA. These and other assays are compared and summarized in terms of characteristics including biologic relevance, sensitivity, specificity, and suitability for different laboratory and clinical applications.