In Kibera, a large informal settlement in Nairobi, a school-based vaccination campaign launched in early 2025 has delivered the typhoid conjugate vaccine (TCV) to more than 200,000 children aged nine months to 15 years. The campaign, run by Kenya's Ministry of Health with support from Gavi and WHO, aims to curb one of the most persistent endemic diseases in the region. Yet adults, who bear a substantial share of the typhoid burden, remain entirely unprotected by the vaccine. This age-based split reflects cost (Gavi does not fund adult doses), policy (Kenya's immunization strategy excludes adults), and donor priorities (no major funder has committed to adult TCV). It also carries consequences for antibiotic resistance and outbreak control.

Typhoid fever, caused by Salmonella enterica serovar Typhi, is a systemic bacterial illness transmitted through contaminated food and water. In Kibera, where roughly 70% of households lack piped water and shared latrines are the norm, transmission is relentless. Incidence rates in informal settlements across sub-Saharan Africa range from 100 to 800 cases per 100,000 person-years, with peaks during rainy seasons. The TCV, prequalified by WHO in 2017, offers a single-dose efficacy estimated at 80–90% and requires no booster. It is a powerful tool — but only for those who receive it.

Kibera’s Typhoid Vaccine Gap Splits by Age

The school-based campaign targeted children because they are the most feasible group to reach through existing infrastructure. Schools in Kibera, though overcrowded, provide a fixed point for vaccination teams. Parents bring younger siblings, and community health workers canvas households near schools. The result: over 200,000 children vaccinated in a matter of months, a remarkable operational achievement.

But the decision to exclude adults was not primarily epidemiological. Adults in Kibera face typhoid incidence rates comparable to children, with some studies showing higher rates in young adults aged 20–39. They are also more likely to experience severe disease, partly because they delay seeking care. In a 2023 survey in Kibera, adult typhoid patients presented on average five days after symptom onset, compared with two days for children. Late treatment means more complications — intestinal perforation, bacteremia — and more antibiotic use. The program's narrow age focus reflects a global pattern. Most typhoid vaccination campaigns, from Bangladesh to Nepal, have targeted children under 15. The rationale is partly immunological: children are thought to be the primary transmitters of infection in household settings. But modeling studies from the International Vaccine Institute suggest that vaccinating school-age children alone reduces overall community transmission by only 30–40%. To achieve herd immunity, coverage needs to extend to at least 60% of the total population, including adults.

In Kibera, the gap is visible. At the Mbagathi sub-county hospital, clinicians note that adult typhoid cases continue to fill wards. “We see the same pattern every rainy season,” said a senior medical officer who asked not to be named. “Children come in vaccinated and mild; adults come in sicker, with resistant strains.” The vaccine gap, in effect, creates a two-tier typhoid experience.

Why Adults Remain Unvaccinated: Cost and Policy

The cost of TCV is modest — around $0.50 to $1.00 per dose for pediatric procurement through Gavi. But adult doses are priced two to three times higher, because Gavi's negotiated rates apply only to children under 15. For a single adult campaign in Nairobi County, covering roughly 2 million adults, the vaccine cost alone would exceed $3 million. Add delivery, cold chain, and demand generation, and the total approaches $5–8 million.

No routine adult typhoid program exists in Kenya. The country's 2024–2028 immunization strategy, aligned with the WHO's Global Vaccine Action Plan, prioritizes children under five and school-age groups. Adults are mentioned only in the context of catch-up campaigns for measles and tetanus. The technical working group that designed the TCV introduction explicitly considered adult vaccination but deferred it, citing cost-effectiveness thresholds. At a cost per dose above $2, adult vaccination exceeds the $50 per disability-adjusted life year (DALY) averted benchmark that Kenya uses for vaccine decisions.

Global funding dynamics reinforce the age divide. Gavi, the Vaccine Alliance, finances TCV for children in eligible countries but does not cover adult doses. The WHO's 2019 typhoid vaccine position paper notes that “adult vaccination may be considered in high-risk settings” but stops short of a recommendation. In practice, no national program has yet funded adult TCV. Even in Bangladesh, which introduced TCV in 2021 and has one of the most proactive typhoid control programs, adult vaccination remains a pilot.

Kenya's Ministry of Health has explored targeted vaccination for high-risk adult groups — food handlers, health workers, and residents of outbreak-prone areas. A 2024 feasibility study estimated that vaccinating 500,000 adults in Kibera and similar settlements would cost $2–4 million. But donor interest has been tepid. “Everyone agrees it would be good,” a ministry official said. “But no one has the money.”

Antibiotic Resistance Threatens Typhoid Treatment

The vaccine gap matters more now because the antibiotics used to treat typhoid are failing. Extensively drug-resistant (XDR) Salmonella Typhi, first identified in Pakistan in 2016, has spread to at least 10 countries. XDR strains are resistant to chloramphenicol, ampicillin, co-trimoxazole, fluoroquinolones, and third-generation cephalosporins. In Kenya, the dominant circulating strain remains multi-drug resistant (MDR) — resistant to first-line drugs but still susceptible to azithromycin and ceftriaxone. But XDR has been detected in neighboring Uganda and Tanzania. Modeling suggests it could reach Kibera within two to three years.

Adult patients are at the center of this threat. Because adults often delay care, they are more likely to receive empiric broad-spectrum antibiotics before a culture result is available. In Kibera, where laboratory capacity is limited, clinicians frequently prescribe azithromycin or ceftriaxone based on clinical suspicion alone. This practice fuels resistance. A 2022 study in Nairobi found that 40% of adult typhoid patients had received at least one antibiotic before presenting to hospital, and nearly half of those isolates showed reduced susceptibility to the drug used.

Resistance surveillance in informal settlements is sparse. The Kenya Medical Research Institute (KEMRI) runs a sentinel site at Kibera's Mbagathi hospital, but sample sizes are small. In 2023, only 120 blood cultures were processed from suspected typhoid cases in Kibera. Without robust data, clinicians rely on outdated antibiograms. “We treat based on what we saw last year,” a physician said. “But last year's pattern may not be next year's.”

The pipeline for new typhoid antibiotics is nearly dry. Only one novel compound, cefiderocol, is in late-stage development for typhoid, and it is not yet approved in Africa. The WHO's 2024 antibacterial pipeline report lists typhoid as a priority pathogen, but no new oral drugs are expected before 2030. Vaccination is the only sustainable tool to reduce antibiotic pressure.

Water and Sanitation Gaps Fuel Persistent Transmission

Vaccination alone cannot break the typhoid cycle in Kibera. The settlement's water and sanitation infrastructure is chronically inadequate. An estimated 70% of households lack access to piped water and rely on boreholes, water vendors, or shallow wells. A 2023 water quality survey found that 45% of borehole samples in Kibera contained fecal coliforms, indicating contamination. Shared latrines — often serving 50 or more people — are frequently overflowing, and open defecation is practiced in some areas.

Transmission spikes during the rainy seasons, typically March–May and October–December. Typhoid incidence in Kibera increases two- to threefold during these months, as flooding spreads sewage into water sources. A 2021 study estimated that 60% of typhoid cases in Kibera were attributable to contaminated water consumed outside the home — from street vendors, schools, or workplaces. Adults, who spend more time away from home, face higher exposure from these sources.

Adults also play a key role in household transmission. Infected adults who prepare food can contaminate meals, infecting children even if the children are partially protected by vaccine. A modeling study from the University of Nairobi found that vaccinating adults could reduce pediatric typhoid cases by an additional 25% beyond child-only vaccination, by interrupting this food-handling link.

Water, sanitation, and hygiene (WASH) interventions remain underfunded. Kibera's water network is mostly informal, with private vendors selling water at prices 5–10 times higher than municipal rates. The Nairobi City Water and Sewerage Company has no active plans to extend piped water into the settlement's interior. Until WASH improves, typhoid will continue to circulate, and the vaccine will serve as a partial shield rather than a full solution.

Lessons from Other Endemic Settings: Bangladesh and Nepal

Bangladesh introduced TCV into its routine immunization program in 2021, targeting children aged 9 months to 15 years. A 2023 evaluation found that pediatric typhoid cases in Dhaka's slums fell by 55% within two years. But adult cases declined only 10–15%, and overall community transmission persisted. The Bangladesh government is now piloting adult TCV in two urban wards, but has not scaled it nationally due to cost. The pilot covers approximately 200,000 adults, with vaccination sites at markets and community centers. Early results from 2024 show a 40% reduction in adult typhoid cases in pilot areas, though the sample size is small. The pilot's cost per dose was $2.50, higher than the pediatric rate, and the government is seeking additional donor support to expand.

Nepal's 2022 campaign, also school-based, achieved similar results. A cluster-randomized trial in Lalitpur reported a 60% reduction in pediatric typhoid cases. But adult incidence remained unchanged. Modeling by the International Vaccine Institute suggested that adding adult vaccination at 50% coverage would reduce total cases by an additional 30% and would be cost-effective at $50 per DALY averted — the same threshold that Kenya uses. Yet no national program has adopted adult TCV. Nepal's Ministry of Health has considered a targeted campaign for food handlers in Kathmandu, but the plan remains unfunded.

Both countries highlight a common pattern: child-only vaccination reduces disease but does not eliminate transmission. Adults serve as a reservoir, and in settings with poor sanitation, the pathogen persists. The WHO's Strategic Advisory Group of Experts on Immunization (SAGE) noted in 2024 that “adult vaccination may be necessary in high-burden settings to achieve elimination goals,” but stopped short of a formal recommendation, citing insufficient evidence on programmatic feasibility.

Kenya could become a test case. With Kibera's campaign already operational, adding an adult component would require relatively modest incremental investment. But the government is waiting for guidance from the Africa CDC and WHO. “We don't want to be the first to do it,” a health official said. “If it fails, we'll be blamed.”

What Adult Vaccination Would Take: Logistics and Cost

Mounting an adult TCV campaign in Kibera would require a different delivery model than school-based vaccination. Adults are not captive in schools; they work long hours, often in informal jobs with no sick leave. Vaccination sites would need to be located at markets, bus stops, health clinics, and workplaces. Community health workers — already used for polio and measles campaigns — could administer doses at doorsteps or during evening hours.

Cold chain capacity is a constraint. TCV requires storage at 2–8°C, and Kibera's health facilities already struggle with refrigerator space for routine vaccines. An adult campaign would require additional cold chain equipment, either solar-powered fridges or cold boxes. The cost of expanding cold chain for a one-time campaign is estimated at $500,000–1 million.

Demand generation is another hurdle. Adult vaccine acceptance in Kenya is low for most vaccines beyond tetanus. A 2023 survey in Kibera found that only 40% of adults would accept a typhoid vaccine if offered, citing concerns about side effects and low perceived risk. Social mobilization — using radio, community meetings, and religious leaders — would be needed to raise awareness. That adds cost and time.

Financing remains the biggest barrier. Gavi does not fund adult doses, and Kenya's domestic health budget is stretched. The Ministry of Health's 2025–2026 budget allocates $12 million for all immunization activities, of which TCV for children consumes $2 million. Adding adult vaccination would require a 20–30% increase in the immunization line item. Donors like the Bill & Melinda Gates Foundation have expressed interest in adult TCV but have not committed funds. “The economics are not there yet,” a foundation spokesperson said.

A Narrow Window for Closing the Immunity Gap

The window for action is narrowing. XDR typhoid is spreading across East Africa. In 2024, an outbreak in Kampala, Uganda, involved a strain resistant to azithromycin and ceftriaxone, leaving clinicians with no oral options. If XDR reaches Kibera, the consequences could be severe. An outbreak in a population where adults are unvaccinated and antibiotics are limited could cause hundreds of deaths.

Vaccinating adults now would prevent future resistance-driven outbreaks. It would reduce antibiotic use, slow resistance emergence, and protect a population that currently relies on increasingly ineffective drugs. The cost of inaction can be measured in DALYs lost and in the potential for a regional epidemic.

Kenya's National Immunization Technical Advisory Group (NITAG) is scheduled to review adult TCV in 2027. The decision will depend on new evidence from Bangladesh and Nepal, as well as domestic cost-effectiveness data. But waiting three years carries risk. By then, the XDR strain may already be circulating. Community health workers in Kibera see the urgency every day. “The children are protected, but their parents are not,” said one worker. “We tell them to wash hands, boil water. But they are tired. They want the vaccine too.”

Kenya's NITAG should expedite its adult TCV review to 2026, and Gavi should pilot adult dose financing. The cost of a pilot — roughly $2–4 million for 500,000 adults — is modest compared to the potential cost of an XDR outbreak. Without such steps, the immunity gap will persist, and the gains from child vaccination risk being eroded by unchecked transmission in adults.

This article is for informational purposes only and does not constitute medical advice. Individual vaccination decisions should be made in consultation with a qualified health professional.