Immunizations, Active

Four types of surveys are commonly employed to estimate vaccination coverage (Table 1). The Demographic and Health Surveys (DHS) [16] and Multiple Indicator Cluster Surveys (MICS) [17] are probability sample surveys, in which each household has a known and nonzero probability of being selected in the sample. There have been about 10–15 DHS and 20 MICS per year since 1995. These large, important, and generally well-conducted household surveys, which are used to collect data about many aspects of health, are described in detail in a companion paper in this Collection [18] (link).
The Expanded Programme on Immunization (EPI) cluster survey was developed by the WHO and was described in 1982 as a practical tool to quickly estimate coverage to within ±10 percentage points of the point estimate [19] (link). The original EPI survey method selects 30 clusters from which seven children in each cluster are selected using the “random start, systematic search” method. Specifically, a starting dwelling is chosen by starting at a central location in the village or town, selecting a direction at random, counting the dwellings lying in that direction up to the edge of the village, and selecting one of them randomly; adjacent households are then visited until seven children aged 12–23 months have been enrolled [20] ,[21] . The central starting location may bias the method to include households with good access to vaccination, so it is difficult to assign unbiased probabilities of selection to the households using this method, which does not meet the above criteria for a probability sample and is, therefore, a “non-probability sampling” survey method [22] (link). EPI surveys are widely used at national and sub-national levels, but there is no central database of results, so the total number of surveys conducted is unknown. Adaptations of the EPI survey have incorporated probability sampling at the final stage of sample selection [22] (link)–[26] (link), and the updated WHO guidelines [21] as well as a recent companion manual on hepatitis B immunization surveys emphasize the need for probability sampling for scientifically robust estimates of coverage [27] .
The main design differences between EPI surveys (if probability sampling is used) and DHS or MICS surveys is that EPI surveys focus specifically on vaccination data while DHS and MICS surveys cover a wide range of population and health topics and include a much larger sample size. In addition, field implementation of EPI surveys is variable and often done without external technical assistance, while the DHS and MICS are highly standardized and have substantial technical assistance and quality control.
A final household survey method commonly used to estimate health intervention coverage in low- and middle-income countries is Lot Quality Assurance Sampling (LQAS). LQAS surveys use a stratified sampling approach to classify “lots,” which might be districts, health units, or catchment areas, as having either “adequate” or “inadequate” coverage of various public health interventions. For vaccination coverage measurement, LQAS is “nested” within a cluster survey to evaluate neonatal tetanus elimination [28] (link), coverage of yellow fever vaccination [29] (link), and coverage of meningococcal vaccine campaigns [30] (link), and to monitor polio vaccination coverage after supplementary immunization activities [31] .

Using the calibrated Status Quo no-new-vaccine model, we simulated Basecase scenarios over 2025–2050 for each product with characteristics informed a priori by clinical trial data and expert opinion.^{13 (link),14 (link)} The Basecase M72/AS01_E scenario assumed a 50% efficacy prevention of disease vaccine with 10-years protection, efficacious with any infection status aside from active disease at vaccination. We assumed the vaccine would be introduced in 2030 routinely to those aged 15 (reaching 80% coverage) and as a campaign for ages 16–34 (reaching 70% coverage), with a repeat campaign in 2040. Based on expert advice, the vaccine price was $2.50 per dose, assuming two doses per course.
The Basecase BCG-revaccination scenario assumed a 45% efficacy vaccine to prevent infection with 10-years protection, and efficacious without infection at time of vaccination. We assumed the vaccine would be introduced in 2025 routinely to those aged 10 (reaching 80% coverage) and as a campaign for ages 11–18 (reaching 80% coverage) with repeat campaigns in 2035 and 2045. Based on the average estimated BCG price from UNICEF,²² the vaccine price was set at US$0.17 per dose, assuming one dose per course.
Vaccine introduction costs for both vaccine products were assumed to be US$2.40 (95% uncertainty interval = 1.20–4.80) per individual in the targeted age group based on vaccine introduction support policy from Gavi, the Vaccine Alliance.²³ A further US$0.11 (0.06–0.22) supply costs and US$2.50 (1.00–5.00) delivery costs per dose were included,²⁴ as well as US$0.94 (0.13–1.52) in patient and caregiver productivity losses per dose, to account for the time taken to receive vaccination.^{25 (link),26} We assumed a 5% wastage rate.
Through consultation with vaccine and country-specific experts, we established specific M72/AS01_E and BCG-revaccination Policy Scenarios and Vaccine Characteristic and Coverage Scenarios. Policy Scenarios represented features of vaccination strategy under the control of decision-makers, which compared different age groups to target for vaccination. Vaccine Characteristic and Coverage Scenarios represented current uncertainties around vaccine performance and uptake, in which we varied unknowns in vaccine profile (such as efficacy, duration of protection, mechanism of effect) and achieved coverage, univariately from each Basecase scenario. We compared Policy Scenarios to identify the optimal implementation approach, and Vaccine Characteristic and Coverage Scenarios to quantify the impact of different sources of uncertainty. (Table 1).

Twelve healthy 4-week-old piglets without P. multocida antibodies were randomly divided into three groups (n = 4 each). The vaccinated groups were immunized intramuscularly with 2 mL of (1) rPMT-NC + CpG, (2) rPMT-NC + w/o/w, or (3) PBS (Table 1). Piglets were boosted with the same vaccine at 2 weeks after the primary immunization. All piglets were challenged intranasally with 1 × 10⁸ CFU/mL P. multocida serotype A 4 weeks after primary immunization [16 (link)]. The antibody titre was detected by blood samples taken at 0, 2 and 4 weeks after primary immunization. The piglets were monitored daily for clinical signs, body temperature (fever was defined as rectal temperature > 39.5 °C), and body weight and were sacrificed for necropsy 14 days after challenge. Pathological examination was performed by the Veterinary Pathology Department of NPUST, and the lesion score was calculated based on the area of lesions in an organ, where no lesion = 0, lesion area < 33% = 1, lesion area 33–66% = 2, and lesion area > 66% = 3 [3 (link)].Table 1

The active ingredients of vaccines in this study

Vaccinea	Adjuvant
Trial 1. Plasmid CpG adjuvant effect test
1. rPMT-NCb + CpG	CpG (200 μg/mL)
2. rPMT-NC + w/o/w	w/o/w
3. Control (PBS)	–
Trial 2. rSly adjuvant dose-dependent test
4. rPMT-NC + w/o/w + rSly	rSly (100 μg/mL)
5. rPMT-NC + w/o/w + rSly	rSly (150 μg/mL)
6. Control (PBS)	–
Trial 3. Comparison with various adjuvants
7. rPMT-NC + w/o/w + rSly	rSly (100 μg/mL)
8. rPMT-NC + w/o/w + CpG	CpG (200 μg/mL)
9. rPMT-NC	–
10. Commercial vaccinec	Al-gel
11. Control (PBS)	–

^aPig immunizaction vaccine with 2 mL by I.M.

^brPMT-NC (200 μg/mL).

^cIngredient: B. bronchiseptica (1 × 10⁹ CFU), P. multocida type A (1 × 10⁹ CFU).

P. multocida type D (1 × 10⁹ CFU), rsPMT/tox1 (20 μg), rsPMT/tox2 (20 μg), rsPMT/tox7 (20 μg), Adjuvant: Al-gel.