Last-mile Delivery Increases Vaccine Uptake in Sierra Leone

"Access, amongst other approaches like communication, is crucial to achieving vaccine equity in developing countries, and will likely be relevant to the new malaria vaccine roll-out and other health products and services." - Niccolò F. Meriggi

Less than 30% of people in Africa received a dose of the COVID-19 vaccine even 18 months after vaccine development. Motivated by the observation that residents of remote, rural areas of Sierra Leone faced severe access difficulties, this group of researchers conducted an intervention with last-mile delivery of COVID-19 vaccine doses and health professionals to the most inaccessible areas, along with community mobilisation. The approach was in keeping with the acknowledgement by behavioural scientists of an excessive focus on individual behavioural peculiarities ("i-frame") at the expense of systemic solutions ("s-frame"). This paper describes the intervention and the cluster randomised controlled trial (RCT) conducted in 150 rural villages to test it.

To understand why vaccination rates remain low, the researchers assembled data on vaccination beliefs, hesitancy, and access from several countries in late 2021. Nationally representative data from Sierra Leone revealed that obtaining access to a COVID-19 vaccine required the average person in to travel three and a half hours each way to the nearest vaccination centre at a cost that exceeds 1 week of wages. This finding motivated the design of the intervention, implemented in March–April 2022 in partnership with the Sierra Leone Ministry of Health and Sanitation (MoHS) and the international non-governmental organisation (NGO) Concern Worldwide.

On the first day of the intervention, a social mobilisation team - trained and supervised by the MoHS - organised a conversation with all village leaders, including the town chief, mammy queen, town elders, the youth leaders and religious leaders, and any other important stakeholders. The mobilization team explained the purpose of the visit, answered questions about the available vaccines, and asked leaders for their cooperation in encouraging eligible community members to take the COVID-19 vaccine. Social mobilisers then asked leaders to convene a community meeting that same evening (when people return home from farms) to allow mobilisers to talk directly with all village residents about vaccine efficacy and safety, to explain the importance of getting vaccinated, and to address villagers' questions and concerns. This process ended with social mobilisers explaining the location and timing of the mobile vaccination site they were about to set up.

Vaccine doses, nurses to administer vaccines, and MoHS staff who could register the vaccinated were brought into the community either the same evening or early the next morning. The vaccine doses and staff often travelled on motorbikes or on boats given the difficult terrain they had to traverse to reach these remote communities. Once the team was in place, the temporary vaccination site started operating in a central location in the village; walking distances to the vaccination site were short. The vaccination site remained operational from sunrise to sunset over the next 2-3 days, which enabled people to visit when convenient.

During this time, the mobilisers continued to provide vaccine information to various community members. The researchers randomised the exact nature of these additional mobilisation activities. Half the treatment villages were randomised into an individualised door-to-door campaign, whereby social mobilisers went to 20 randomly selected structures to privately discuss any concerns about that vaccine that the household residents had and to encourage them to visit the vaccination site. The other 50 treatment communities were randomised into small-group outreach, whereby mobilisers reached out to social groups who gathered at fixed spots in and around the villages (for example, groups of farmers in fields, mosque attendees, or women collecting water). Social mobilisers engaged the group to have joint conversations about the vaccines.

One hundred communities were randomly assigned to receive the intervention; 50 were assigned to the control group. In total, the teams vaccinated 4,771 people aged 12 years or above. At baseline, there were on average about 5 people vaccinated in control villages and about 9 people in treatment villages; after the intervention was implemented over the subsequent 2-3 days, the number of vaccinated individuals increased to about 55 people on average per treatment site, which represents an increase in the immunisation rate by about 26 percentage points. All in all, the findings show that the vaccine intervention tripled vaccination rates within 48-72 hours.

Furthermore, auxiliary populations visited the community vaccination points, which more than doubled the number of inoculations administered. Among individuals vaccinated who were not enumerated in the census, 53% (12-13 people per treatment community) were visitors who came from nearby villages to get vaccinated, whereas the remaining 47% (11-12 people) included short-term, circular commuters or migrant returnees who were not present on the day of the census and could not be matched to the listing records, as well as individuals whose community of origin was unknown.

The treatment effect was 7 percentage points larger for men than for women and 12 percentage points larger for the over-55-year age group compared with the 18-24 years age group.

The evidence on whether the door-to-door or small-group activities were more effective was mixed. Across communities, the door-to-door programme increased the adult vaccination rate by about 29 percentage points compared with 23 percentage points in villages assigned to the small-group mobilisation activities. However, when the researchers studied individual households randomly assigned to a visit against those who are not within door-to-door villages, they did not detect any differential uptake.

The researchers collected individual-level data in all treatment villages after the intervention from both vaccine takers and non-takers. These data can shed some light on why and how the intervention was more or less successful for certain types of people:

• Meeting attendance: Within the subset of people who stated in the baseline survey who said they were unwilling to receive a vaccine, 53.8% of those who attended meetings ultimately took the vaccine, whereas the vaccination rate was only 14.4% among those who did not attend. Even within the converse subgroup (those who said at baseline they were willing to take the vaccine), meeting attendance was strongly predictive of subsequent vaccine uptake: 64.6% vaccination rate among attendees and 39.4% among non-attendees. "These are not causal estimates, but the size and direction of these correlations suggest that the information shared in the meeting, and the answers that were provided to the community's questions, are unlikely to have dissuaded people from getting vaccinated."
• Vaccination knowledge and trust: The treatment improved people's knowledge about vaccines. The change in knowledge implies that the intervention was not solely about improving access. That is, the community interactions and the information shared were also relevant parts of the intervention package.

The model proved to be 76% cheaper than the average cost of similar interventions. The additional people vaccinated per intervention site translated to an implementation cost of US$33 per person vaccinated. Transportation to reach remote villages accounted for a large share of total intervention costs. Therefore, bundling multiple maternal and child health interventions in the same visit would further reduce costs per person treated.

To benchmark the results against other vaccination strategies, the researchers conducted a comprehensive literature review that identified 235 distinct interventions in 144 RCT studies that used information, nudges, community engagement, social signalling, and non-financial and financial incentives to increase vaccination rates across many settings around the world. More than one-third of these interventions produced null effects. Here, the access intervention produced a larger percentage point effect size than 223 (95%) of the treatments reviewed. Per the researchers: "This result is not surprising because vaccinating the first 50% of the population in remote parts of low-income countries requires solving the fundamental problem of access....Once access issues are addressed, misinformation and hesitancy may loom large in the effort to vaccinate the last 20% of the population of high-income countries who stubbornly hold out, and this is the target of the bulk of the literature."

In response to the study results:

• The researchers began building the necessary coalition to implement a bundling strategy (bundling COVID-19 vaccines with other necessary mother, infant, and child health interventions that can be simultaneously delivered on the same trip) to improve the cost-effectiveness and scalability of this intervention.
• Also under consideration: replicating such a programme in neighbouring countries with similar last-mile delivery challenges. "The majority of people in sub-Saharan Africa live in rural areas..., so overcoming access challenges through such initiatives holds enormous potential for both achieving vaccine equity and maximizing global coverage."
• The researchers are investigating how the last-mile intervention for COVID-19 vaccines can be expanded to deliver other priority vaccinations, including routine immunisations for measles and polio and vaccination against human papillomavirus (HPV).