ProQuad Mechanism of Action

Pharmacotherapeutic group: Viral Vaccine. ATC code: J07BD54.
Therapeutic Class: ProQuad is a combined attenuated live virus vaccine containing measles, mumps, rubella, and varicella viruses.
Pharmacology: Measles, mumps, rubella, and varicella are 4 common childhood diseases caused by measles virus, mumps virus, rubella virus, and varicella virus, respectively. These diseases may be associated with serious complications and/or death. For example, measles can be associated with pneumonia and encephalitis; mumps can be associated with aseptic meningitis, deafness, and orchitis; rubella occurring during pregnancy can cause congenital rubella syndrome in the infants of infected mothers; and wild-type varicella can be associated with bacterial superinfection, pneumonia, encephalitis, and Reye syndrome.
Pharmacodynamics/Pharmacokinetics: Not Applicable.
Efficacy: Formal studies to evaluate the efficacy of ProQuad have not been performed. However, the efficacy of M-M-R II and VARIVAX has been demonstrated in numerous studies.
Efficacy of the measles, mumps, and rubella components of ProQuad was previously established in a series of double-blind controlled field trials with the monovalent vaccines produced by Merck Sharp & Dohme LLC, Rahway, NJ 07065, USA which demonstrated a high degree of protective efficacy. In these studies seroconversion in response to vaccination against measles, mumps, and rubella paralleled protection from these diseases. ProQuad elicits rates of antibody responses against measles, mumps, and rubella similar to those observed after vaccination with M-M-R II.
More than 518 million doses of M-M-R II have been distributed worldwide (1978 to 2007). Widespread use of a 2-dose vaccination schedule in the United States and countries such as Finland and Sweden has led to a >99% reduction in the incidence of each of the 3 targeted diseases. Vaccination against measles, mumps, and rubella has led to a significant reduction in the incidence of these diseases.
In combined clinical trials of VARIVAX, the protective efficacy of the vaccine against all forms of varicella ranged from 81 to 100%. In a large case-control study, the vaccine was estimated to be 85% effective against all forms of varicella and 97% effective against moderately severe and severe disease. Long-term estimated efficacy for the vaccine against all forms of varicella over 10 years was 94%. Antibody responses against varicella virus ≥5 units/mL in the glycoprotein enzyme-linked immunosorbent assay (gpELISA, a highly sensitive assay which is not commercially available) have been shown to be highly correlated with long-term protection. Clinical studies have shown that vaccination with ProQuad elicits rates of antibody responses against varicella virus ≥5 units/mL in the gpELISA similar to those observed after vaccination with VARIVAX.
Immunogenicity: Immunogenicity was studied in children 12 through 23 months of age with a negative clinical history of measles, mumps, rubella, and varicella who participated in 5 randomized clinical trials. The immunogenicity of the current refrigerator-stable formulation was shown to be similar to the immunogenicity of the earlier formulation of ProQuad. Clinical trials also established that the earlier formulation of ProQuad is similar to the individual component vaccines (M-M-R II and VARIVAX), which are currently used in routine vaccination in some countries.
Clinical trials involving 6987 subjects who received ProQuad demonstrated detectable immune responses to measles, mumps, rubella, and varicella in a high proportion of individuals. The presence of detectable antibody was assessed by an appropriately sensitive enzyme-linked immunosorbent assay (ELISA) for measles, mumps (wild-type and vaccine-type strains), and rubella, and by gpELISA for varicella. Following a single dose of ProQuad, the vaccine response rates were 97.7% for measles, 96.3 to 98.8% for mumps, and 98.8% for rubella. The vaccine response rate was 90.9% for varicella based on an antibody response rate ≥5 gpELISA units/mL (a response rate that has been shown to be highly correlated with long-term protection). These results were similar to the immune response rates induced by concomitant administration of M-M-R II and VARIVAX at separate injection sites.
Children who received a second dose of ProQuad: In 2 clinical trials, 1035 subjects were administered a second dose of ProQuad subcutaneously approximately 3 months after the first dose. The vaccine response rates were 99.4% for measles, 99.9% for mumps, 98.3% for rubella, and 99.4% for varicella (≥5 gpELISA units/mL). The geometric mean titers (GMTs) following the second dose of ProQuad increased approximately 2-fold each for measles, mumps, and rubella, and approximately 41-fold for varicella. In these trials, the rates of adverse experiences after the second dose of ProQuad were generally similar to, or lower than, those seen with the first dose. The fever rate was lower after the second dose than after the first dose.
Children who received ProQuad at 4 through 6 years of age after primary vaccination with M-M-R II and VARIVAX: The immunogenicity and safety of ProQuad were evaluated in a clinical trial involving 799 subjects 4 through 6 years of age who had received M-M-R II and VARIVAX at least 1 month prior to study entry. Following the dose of ProQuad administered subcutaneously, GMTs for measles, mumps, rubella, and varicella were similar to those following a second dose of M-M-R II and VARIVAX administered concomitantly at separate injection sites. Additionally, GMTs for measles, mumps, and rubella were similar to those following a second dose of M-M-R II given concomitantly with placebo. In this trial, the rates and types of adverse experiences seen in the group that received ProQuad were generally similar to those seen in the control groups.
Immunogenicity Following 2 Doses of ProQuad Administered Intramuscularly or Subcutaneously: In an open label clinical trial 405 children 12 through 18 months of age received two doses of ProQuad, administered 30 days apart, either intramuscularly (n=202) or subcutaneously (n=203). Antibody responses to measles, mumps, rubella, and varicella viruses were measured by ELISAs using sera obtained 30 days post-dose 1, and 6 weeks post-dose 2. For anti-measles virus, anti-mumps virus, anti-rubella virus, and anti-varicella virus, seroresponse rates were defined as the percentage of children seronegative at baseline who achieved antibody titers above the respective seroresponse threshold for each assay 30 days post-dose 1 and 6 weeks post-dose 2. Seroresponse thresholds were defined as 255 mIU/mL, 10 EU/mL, 10 IU/mL, and 5 gpELISA units for anti-measles virus, anti-mumps virus, anti-rubella virus, and anti-varicella virus antibodies, respectively after each dose. For each vaccine antigen at least 87% of enrolled children were seronegative at baseline.
In the pre-specified primary analysis, the seroresponse rates to measles, mumps, rubella, and varicella viruses after dose 2 were noninferior in the intramuscular group compared to the subcutaneous group (lower bound of the 95% confidence interval for the difference in seroresponse rates [intramuscular group minus subcutaneous group] was >-10%). The proportions of children achieving antibody titers above the seroresponse thresholds for measles, mumps, rubella, and varicella viruses after dose 1 were as follows: 100%, 97.4%, 98.4%, and 98.6%, respectively, in the intramuscular group and 97.3%, 91.3%, 100%, and 98.5%, respectively, in the subcutaneous group. The proportions of children achieving antibody titers above the seroresponse thresholds for measles, mumps, rubella, and varicella viruses after dose 2 were as follows: 100%, 99.3%, 100%, and 100%, respectively, in the intramuscular group and 100%, 99.3%, 99.2%, and 99.3%, respectively, in the subcutaneous group.
Persistence of Immune Response: The persistence of antibody at 1 year after vaccination was evaluated in a subset of 2108 subjects who were involved in 1 clinical trial. The antibody persistence rates 1 year post-vaccination in recipients of a single dose of ProQuad were 98.9% (1722/1741) for measles, 96.7% (1676/1733) for mumps, 99.6% (1796/1804) for rubella, and 97.5% (1512/1550) for varicella (≥5 gpELISA units/mL).
Experience with M-M-R II demonstrates that antibodies to measles, mumps, and rubella viruses are still detectable in most individuals 11 to 13 years after primary vaccination. In clinical studies involving healthy subjects who received 1 dose of VARIVAX, detectable varicella antibodies were present in most individuals tested for up to 10 years post-vaccination.
Herpes Zoster: In a clinical trial, 2 cases of herpes zoster were reported in 2108 healthy subjects 12 through 23 months of age who were vaccinated with ProQuad and followed for 1 year. Both cases were unremarkable and no sequelae were reported.
The reported rate of zoster in recipients of VARIVAX appears not to exceed that previously determined in a population-based study of healthy children who had experienced wild-type varicella. In clinical trials, 12 cases of herpes zoster were reported in 9543 vaccinated individuals 12 months through 12 years of age during 84,414 person-years of follow-up. This resulted in a calculated incidence of at least 0.14 cases per 1000 person-years. The incidence of herpes zoster following naturally acquired infection in subjects >5 years of age and persons 5 to 9 years of age has been reported to be 1.1 and 0.51 per 1,000 person-years, respectively. All 12 cases reported after VARIVAX were mild and no sequelae were reported. The long-term effect of VARIVAX on the incidence of herpes zoster is unknown at present.
Post-Exposure Prophylaxis: No clinical data are available for ProQuad administered after exposure to measles, mumps, rubella, or varicella; however, post-exposure prophylaxis has been demonstrated for measles and varicella with measles-containing vaccine and varicella virus vaccine, respectively. Vaccination of susceptible individuals within 3 days of exposure to wild-type measles may provide some protection. Vaccination of susceptible individuals within 3 days of exposure to wild-type varicella may prevent a clinically apparent infection or modify the course of the infection. In addition, there are limited data that indicate that vaccination up to 5 days after exposure to varicella may modify the course of the infection.
Reye Syndrome: Reye syndrome following wild-type varicella infection has occurred in children and adolescents, the majority of whom had received salicylates. In clinical studies of ProQuad and in the clinical studies of VARIVAX, physicians advised subjects not to use salicylates for 6 weeks after vaccination. There were no reports of Reye syndrome in recipients of ProQuad or VARIVAX during these studies.
Studies With Other Vaccines: In a clinical trial involving 1913 healthy subjects 12 through 15 months of age, 949 received ProQuad subcutaneously, Diphtheria and Tetanus Toxoids and Acellular Pertussis Vaccine Adsorbed (DTaP) and Haemophilus b Conjugate (Meningococcal Protein Conjugate) and Hepatitis B (Recombinant) Vaccine concomitantly at separate injection sites. Another 485 healthy subjects received ProQuad at the initial visit followed by DTaP and Haemophilus b Conjugate and Hepatitis B (Recombinant) Vaccine given concomitantly 6 weeks later. No clinically significant differences in adverse experiences were reported between the 2 treatment groups. In addition, another 479 children received M-M-R II and VARIVAX concomitantly at separate injection sites at the initial visit followed by DTaP and Haemophilus b conjugate and Hepatitis B (Recombinant) vaccine given concomitantly 6 weeks later. Seroconversion rates and antibody titers for measles, mumps, rubella, varicella, Hib, and hepatitis B were comparable between the 2 groups. Seroconversion rates and antibody titers for measles, mumps, rubella, varicella, Hib, and hepatitis B were comparable between the 2 groups at approximately 6 weeks post-vaccination, indicating the ProQuad and Haemophilus b Conjugate (Meningococcal Protein Conjugate) and Hepatitis B (Recombinant) Vaccine may be administered concomitantly at separate injection sites. There are insufficient data to support concomitant vaccination with diphtheria, tetanus, and acellular pertussis vaccine.