Immunogenicity, reactogenicity, and IgE-mediated immune responses of a mixed whole-cell and acellular pertussis vaccine schedule in Australian infants: a randomised, double-blind, non-inferiority trial
Authors: Pérez Chacón Gladymar , Estcourt Marie J , Totterdell James , Marsh Julie A , Perrett Kirsten P , Campbell Dianne E , Wood Nicholas , Gold Michael , Waddington Claire S , Sullivan Michael O’ , McAlister Sonia , Curtis Nigel , Jones Mark , McIntyre Peter B , Holt Patrick G , Richmond Peter C , Snelling Tom 
Published: December 2023

Background

In most high-income countries, infant vaccination with acellular pertussis (aP) vaccines is the standard of care for the prevention of pertussis disease. Based on immunological and epidemiological evidence, we hypothesised that substitution of the first aP dose in the vaccination schedule with whole-cell (wP) vaccine might protect against the development of IgE-mediated food allergy. Here we report the results of a randomised comparison of the reactogenicity, immunogenicity, and IgE-mediated immune responses of a mixed wP/aP primary schedule versus the standard aP-only schedule.

Methods

OPTIMUM is a Bayesian, two-stage, double-blind, group sequential trial, enrolling healthy Australian-born infants. At approximately 6 weeks old, participants are randomly assigned (1:1) to a first dose of a pentavalent wP combination vaccine (DTwP-Hib-HepB; Pentabio, PT Bio Farma, Indonesia) versus a hexavalent aP vaccine, which includes inactivated poliovirus vaccine (IPV) types 1, 2, and 3 in its formulation (DTaP-Hib-HepB-IPV; Infanrix Hexa, GlaxoSmithKline, Australia). All infants receive a hexavalent aP vaccine at 4 and 6 months old, as well as a tetravalent aP-based formulation at 18 months old (DTaP-IPV; Infanrix-IPV, GlaxoSmithKline, Australia) to ensure at least three doses of IPV as part of their childhood schedule while preserving blinding. In stage one, pertussis antigen-specific IgG responses were measured before and approximately one month after the 6-month aP vaccine doses. The immunogenicity of the mixed schedule (wP/aP/aP) was defined as being non-inferior to that of the aP-only schedule (aP/aP/aP) using a non-inferiority margin of 2/3 on the ratio of the geometric mean concentrations of pertussis toxin (PT) IgG approximately one month after the 6-month aP dose. Solicited adverse reactions were summarised by study arm and included all children who received the first dose of either wP or aP. Parental acceptance was assessed using a 5-point Likert scale. The trial is registered with ANZCTR (ACTRN12617000065392p).

Results

Between March 7, 2018 and January 13, 2020, 150 infants were randomised (75 per arm). Demographic and baseline characteristics were balanced across the study arms. Most infants were born to aP-vaccinated mothers. In the intent-to-treat analysis, PT-IgG responses of the mixed schedule were non-inferior to the aP-only schedule approximately one month after a 6-month aP dose [geometric mean ratio (GMR) = 0·98, 95% Bayesian credible interval (0·77 to 1·26); probability (GMR > 2/3) > 0·99]. Severe solicited systemic adverse reactions were reported among 14 of 74 (19%) infants after a first dose of wP and among 8 of 72 (11%) infants after a first dose of aP; irritability after the first dose of pertussis-containing vaccine was the most frequent severe event (11 of 74 [15%] wP recipients versus 7 of 72 [10%] aP recipients). Within 6 months of enrolment, 7 serious adverse events were reported, with none deemed related to the study vaccines. Parental acceptance of the mixed schedule was high (97% would agree to have this schedule again).

Interpretation

The mixed wP/aP schedule was associated with more reactions than the aP-only schedule, but these were mostly non-severe. The mixed schedule was well accepted by parents and evoked non-inferior PT-IgG responses after completion of the three-dose primary series.

Funding

Telethon New Children’s Hospital Research Fund and National Health and Medicine Research Council.

Research in context

We searched PubMed on April 17, 2023, for paediatric studies of heterologous priming with whole-cell pertussis (wP) vaccine and acellular pertussis (aP) vaccine, with no language or date restrictions. We used the terms [“whole-cell pertussis vaccine” AND “acellular pertussis vaccine”], OR [“IgE” AND “tetanus toxoid”]. Of the 997 articles retrieved, we found no published randomised comparisons between heterologous versus exclusive primary routine vaccination with either wP or aP-based formulations.

In two observational studies, laboratory-confirmed pertussis disease was less common among school-aged children and adolescents who received wP versus aP as a first dose. A heterologous wP/aP primary schedule (in which the first dose was wP) was associated with lower rates of pertussis disease than an aP-only primary schedule.

In a case-control study, pertussis was less common among children who had received mixed wP/three-component (3c)-aP vaccine (including pertussis toxoid, filamentous haemagglutinin, and pertactin) versus those exclusively primed with 3c-aP vaccine formulations. No evidence of a difference was observed among those vaccinated with a heterologous wP/five-component (5c)-aP primary schedule versus those exclusively primed with a 5c-aP vaccine formulation (including the above-mentioned pertussis antigens as well as fimbriae type 2 and 3). In contrast, another case-control study found that compared to the 5c-aP-only priming strategy, a primary series including one or more doses of a wP vaccine formulation, with reported efficacy against laboratory-confirmed pertussis between 36% (95% CI 14% to 52%) and 48% (95% 37% to 58%), was associated with higher vaccine effectiveness against pertussis disease more than a decade after priming. In none of the case-control analyses was the nature of the heterologous schedules further described.

Two clinical and immunological studies reported that wP-only schedules were associated with lower post-priming tetanus toxoid (TT)-IgE concentrations than homologous priming with aP-containing vaccines. An additional study reported lower TT-IgE concentrations after a first dose of wP versus aP.

Added value of this study

To our knowledge, this is the first trial to evaluate the immunogenicity, reactogenicity, and IgE-mediated immune responses to a mixed primary schedule consisting of a first dose of wP given at approximately 6 weeks old, followed by aP at 4, and 6 months old.

Implications of all the available evidence

This trial provides supporting evidence of the safety and immunogenicity of a mixed wP/aP vaccine schedule in a setting with high maternal pertussis vaccine coverage. The findings warrant further investigation of the comparative clinical effects of a mixed wP/aP versus the standard aP-only schedule.