A rabies campaign can vaccinate thousands of dogs and still miss the herd-immunity target. In Zambia, the biggest obstacle was not simply vaccine supply—it was where dogs lived, how far owners had to travel, and whether communities knew the campaign was happening.

Dog vaccination against rabies is considered one of the most effective strategies at preventing human deaths from rabies and is a key strategy for eliminating dog-mediated human rabies deaths. But traditional vaccination approaches in Zambia rarely collect operational data to assess coverage and inform subsequent campaigns.

Rabies is one of the most lethal infectious diseases, with the highest case fatality rate of all zoonoses. Bites from dogs are responsible for approximately ninety-five percent of the estimated seventy thousand human rabies deaths globally. Asia and Africa have the highest risk for rabies transmission, attributed to relatively low herd immunity in dog populations and the propensity for dogs to roam freely within the community.

Most rabies cases in animals and humans are caused by the dog-maintained rabies virus variant, which is mainly transmitted by domestic, free-roaming dogs. Observations on the relationship between rabies incidence and vaccination coverage in dogs have shown that seventy percent coverage is necessary to eliminate or prevent rabies outbreaks.

Most vaccination campaigns in Zambia have relied on central point vaccination, placing government dog vaccination teams throughout a community with the expectation that dog owners will bring their dogs to the campaign. Despite government-sponsored campaigns since at least twenty thirteen, rabies cases continue to persist, suggesting that critical vaccination thresholds are not being met.

Rabies programs typically describe dog populations in terms of the human to dog ratio, but the human to dog ratio is not constant across all communities. It can differ greatly based on community characteristics, religion, poverty, and other factors, so reliance on a static human to dog ratio can lead to inconsistent post-vaccination herd immunity and persistent rabies cases.

In Lusaka, the Ministry of Fisheries and Livestock historically used an estimated human to dog ratio of forty-five to one, although this information had not been validated. The study conducted post-vaccination evaluations after two mass vaccination campaigns: an urban campaign in Lusaka District in July twenty twenty-two and a rural campaign in Itezhi tezhi District in September twenty twenty-one.

The evaluations assessed vaccination coverage and estimated and characterized the dog population in these areas. In Lusaka, coordinators assigned four vaccination teams, each comprised of four staff, to each central point site for up to three days.

Teams remained in locations until staff decided that adequate vaccination coverage had been achieved, although no quantitative methods informed that decision. Using a human to dog ratio of forty-five to one, the campaign set a goal of vaccinating approximately ten thousand dogs to reach target vaccination coverage of seventy percent.

In Itezhi tezhi, coordinators assigned daily working areas to each vaccination team, with three staff total, via a smartphone-web system called the WVS App. The WVS App was used to visualize the targeted area, and teams began each day assigned to a central point site.

In Lusaka, field survey teams conducted dog sight surveys in six vaccination zones to estimate the free-roaming dog population and assess free-roaming dog vaccination coverage by documenting a vaccination mark, such as wax paint. Teams completed dog sight surveys over two consecutive days to allow for a sight-re-sight analysis using the Lincoln-Peterson formula.

Field survey teams conducted household surveys in nine vaccination zones in Lusaka and eight in Itezhi tezhi to estimate vaccination coverage and the owned dog population, including free-roaming and confined dogs. Teams administered a standardized questionnaire to consenting adults at least eighteen years old, which was used to determine vaccination coverage and human to dog ratios.

Teams initiated post-vaccination household surveys in a vaccination zone once field managers indicated that they were complete. Field teams vaccinated a total of six thousand fifty-four dogs during the Lusaka campaign between July fourth and July twenty-first, twenty twenty-two, averaging one hundred forty-three dogs vaccinated per team per day.

The rate was typically highest on the first day at a central point site, averaging one hundred fifty-six dogs per team per day, and decreased to one hundred thirty dogs per team per day by the third day. During the Itezhi tezhi campaign between September sixth and September fourteenth, twenty twenty-one, field teams vaccinated three thousand nine hundred thirty dogs, averaging seventy-one dogs per team per day.

Surveyors approached eight hundred thirty-eight households, and six hundred seventy-one respondents, or eighty percent, consented to post-vaccination household surveys. Among these six hundred seventy-one households, two hundred sixty-four, or thirty-nine percent, reported owning a total of five hundred forty-five dogs.

In Lusaka, two thousand eight hundred ninety-four household members reported owning two hundred dogs, with a human to dog ratio of fourteen point five. In Itezhi tezhi, one thousand one hundred twelve household members reported owning three hundred forty-five dogs, with a human to dog ratio of three point two.

Among one hundred thirty-four dog-owning households in Lusaka, thirty-two respondents, or twenty-four percent, had no awareness that the campaign had been conducted. Another twenty-nine respondents, or twenty-two percent, were made aware of the campaign after it had already started.

Overall, nearly half, or forty-six percent, of dog owners were not reached through pre-campaign sensitization activities. In Lusaka, pre-adjusted vaccination coverage was highest among confined dogs at sixty-eight percent, followed by sometimes-roaming dogs at fifty-eight percent and always-roaming dogs at twenty-five percent.

Among all free-roaming dogs, vaccination coverage in the past year was fifty-three percent. Nearly half of confined dogs, twenty-four dogs or forty-one percent, were vaccinated through private veterinary services, compared with ten free-roaming dogs, or twenty percent.

Vaccination coverages showed a strong correlation with distance to the central point site in the Lusaka campaign. Dogs residing within two hundred meters of the central point site had coverage of fifty-eight percent, compared to forty-one percent when they resided farther away.

Figure four compares willingness to walk to a central vaccination point with distance from that site. The blue curve shows self-reported willingness, with dotted lines marking the ninety-five percent confidence interval; the red curve adjusts those distances, while pink dots show survey-derived vaccination coverage.

Although all respondents said they would walk one hundred meters, willingness declines with distance, and the adjusted curve remains below the seventy percent vaccination goal across the chart. After adjusting the observed fifty-eight percent coverage within zero to two hundred meters of a central point site for reporting bias, herd immunity was not reached at any distance using the central point vaccination approach.

Coverage declined rapidly after one thousand five hundred meters, and household survey-derived coverages were closely aligned with adjusted reported willingness to walk distances. Extrapolating the associations to the entirety of Zambia produced an estimated total dog population of three million two hundred nine thousand seven hundred forty-nine.

The estimated free-roaming dog population was one million one hundred fifty-six thousand six hundred seventy-one. The largest dog populations reside in rural communities at sixty-two percent, followed by peri-urban communities at twenty-four percent, with fourteen percent in urbanized communities.

Table 1 estimates total and free-roaming dog populations across human population-density bands in Lusaka District and Zambia, with ninety-five percent confidence intervals and human-to-dog ratios. In Lusaka, the total estimate is 185,061 dogs, including 114,257 free-roaming dogs; across Zambia, the corresponding estimates are 3,209,749 and 1,156,671.

The authors use these estimates to show that HDR-based dog counts can differ substantially from previous official estimates using an HDR of 45 to 1. In the rural community of Itezhi tezhi, herd immunity was achieved, whereas vaccination coverage in the urban communities of Lusaka reached only thirty-five percent.

Itezhi tezhi used a hybrid campaign of central point sites followed by a door-to-door approach, alongside a large investment in pre-campaign awareness and App-derived daily guidance for moving vaccination teams. Only nine percent of dog owners in Itezhi tezhi claimed they were unaware of the campaign before it began, and inability to reach the campaign was rarely cited as a barrier.

The contrast identifies campaign design as one primary reason for lower coverage in Lusaka. Because most dogs were found at very low densities, large-scale dog vaccination approaches may face unique challenges in Zambia due to high logistical costs in these settings.

Prioritizing vaccinations in higher-density free-roaming dog populations could maximize effectiveness in resource-limited settings. Private veterinary services were commonly utilized among surveyed dog owners in urbanized communities in Lusaka, suggesting that they are an important collaborator for achieving rabies herd immunity.

With improved knowledge of dog population and ownership characteristics, Zambia is well-prepared to design more effective vaccination campaigns as the rabies elimination program expands. Zambia’s rural campaign achieved herd immunity with door-to-door follow-up and strong pre-campaign awareness, while Lusaka reached only 35%.

Mapping dog populations and partnering with private veterinary services could make future vaccination more effective.