Tanzania risks more measles outbreaks unless children complete both recommended doses of vaccine

MWANZA: Tanzania must strengthen routine immunisation services and ensure that every eligible child receives both recommended doses of the measles-containing vaccine to prevent future outbreaks, a new study has established.

The research, conducted by Dr Fausta Michael, who recently completed her PhD at the Catholic University of Health and Allied Sciences (CUHAS-Bugando) in Mwanza, has exposed persistent gaps in population immunity despite the introduction of the second measles vaccine dose in 2014.

The study examined measles outbreaks across mainland Tanzania between 2018 and 2024, providing evidence of the challenges affecting childhood vaccination programmes and the country’s ability to sustain protection against the highly contagious disease.

Speaking in a special interview with the Daily News in Mwanza yesterday, Dr Fausta said the findings highlight the need for stronger immunisation strategies, improved healthcare delivery and greater attention to children who have not completed their vaccination schedules.

She explained that the research combined national measles surveillance data from all 195 councils in mainland Tanzania with laboratory investigations, interviews with healthcare stakeholders and focus group discussions involving caregivers.

The researchers reviewed 12,253 suspected measles cases reported between 2018 and 2022, alongside another 17,902 suspected cases recorded between 2023 and 2024.

Laboratory investigations involved analysing blood samples to assess immunity levels and examining throat specimens to identify measles virus genotypes circulating in the country.

“We analysed blood samples to assess immunity levels and investigated throat specimens to identify circulating measles genotypes. The findings provide evidence to guide public health interventions and improve childhood vaccination programmes,” she said.

Rising infections expose vaccination gaps

Of the 17,902 suspected cases reported between 2023 and 2024, 11,576, equivalent to 64.6 per cent, were classified as confirmed measles cases based on laboratory evidence, epidemiological links or clinical compatibility.

The findings further revealed a sharp increase in measles transmission in 2023, demonstrating how quickly the disease can spread when population immunity is insufficient.

According to Dr Fausta, the incidence rate increased from 10.4 cases per one million people in 2022 to 163.9 cases per one million people in 2023, before declining to 15.4 cases per one million people in 2024.

“Children under five years consistently carried the greatest disease burden, while Katavi and Tabora recorded the highest incidence rates in 2023, shifting to Pwani and Kigoma regions in 2024,” she explained.

The geographical shifts suggest that measles prevention requires sustained attention across different regions rather than concentrating interventions in areas that previously recorded high infection rates.

More importantly, the study established a strong relationship between vaccination status and the risk of contracting measles.

Dr Fausta said unvaccinated children and those who had received only one dose faced a higher risk of laboratory-confirmed infection than children who had completed the recommended two-dose schedule.

“This aligns with findings from other countries where two doses of measles vaccination have proven to be an effective public health intervention in preventing and eliminating measles,” she said.

She emphasised that completing both doses remains essential because receiving the first dose alone does not provide the same level of protection as completing the recommended schedule.

The findings therefore reinforce the importance of accessible immunisation services, particularly in rural communities where geographical and healthcare delivery challenges may prevent children from receiving their scheduled vaccinations.

Immunity levels remain below protection threshold

Beyond examining reported infections, the researchers assessed population immunity by analysing 526 archived blood samples collected from children who tested negative for recent measles infection.

The results showed that 82.7 per cent of the children had measles-specific immunity, based on immunoglobulin G (IgG) seropositivity.

However, children aged between five and nine years recorded the lowest measles-specific immunity compared with other age groups.

Dr Fausta said the overall immunity level was below the 95 per cent population immunity benchmark associated with herd protection against measles.

“This was below the 95 per cent population immunity benchmark associated with herd protection,” she noted, adding that children who had received both vaccine doses generally demonstrated stronger antibody levels.

Population immunity is particularly important in controlling measles because the virus spreads rapidly through respiratory droplets and airborne particles. When a sufficiently large proportion of people remain susceptible, transmission can continue and outbreaks become more likely.

The vulnerability of children aged five to nine years is particularly concerning because they interact frequently with other children in schools and surrounding communities.

Dr Fausta observed that immunity gaps within this age group could contribute to outbreaks because of their high contact rates in educational institutions and community settings.

The findings point to the importance of looking beyond vaccination coverage among infants and ensuring that children maintain adequate protection as they grow older.

Virus investigations identify circulating genotype

The study also investigated the genetic characteristics of measles viruses circulating in Tanzania to establish whether the outbreaks were associated with the emergence of new viral strains.

According to Dr Fausta, laboratory sequencing identified measles virus genotype B3 in 73 successfully sequenced specimens out of 129 examined.

“The genotype is consistent with strains circulating in East and Southern Africa. Nine distinct sequence variants were identified, including seven newly reported variants submitted to the measles nucleotide surveillance database,” she explained.

The findings suggest that insufficient population immunity, rather than the emergence of a new measles genotype, was the principal factor driving the outbreaks.

This distinction is important for public health planning because it points to weaknesses in vaccination coverage and service delivery as critical areas requiring intervention.

Healthcare delivery challenges undermine vaccination efforts

To understand the factors contributing to the immunity gaps, the researchers interviewed 52 key informants and conducted 10 focus group discussions with caregivers.

Their findings identified several health-system and service-delivery challenges, including vaccine stock-outs, missed vaccination opportunities and reluctance among some healthcare workers to open vaccine vials for fear of wastage.

Dr Fausta said the problem was particularly evident in rural areas, where healthcare workers may hesitate to open vaccine vials when only a few children are available for vaccination.

Such practices can unintentionally deny eligible children access to essential vaccines, even where immunisation services are available.

“These challenges can leave children unprotected even where vaccination services exist,” she cautioned.

She urged healthcare workers to make vaccination status assessment part of every eligible healthcare visit, counsel caregivers on the importance of immunisation and administer missed doses promptly.

She also called on parents and caregivers to take responsibility for ensuring that children complete both recommended doses.

Strengthening routine immunisation

Dr Fausta appealed to immunisation stakeholders to address weaknesses in vaccine supply chains, improve monitoring of second-dose coverage and conduct targeted supplementary immunisation campaigns in communities with significant immunity gaps.

She said surveillance data should be used more effectively to identify underserved populations, strengthen outreach services and ensure reliable vaccine availability.

“Immunisation stakeholders should use surveillance data to identify underserved populations, improve outreach services and ensure reliable vaccine availability,” she said.

She further emphasised that sustainable investment in routine immunisation, accurate vaccination records and community education was essential to protecting children against preventable illnesses and deaths.

Ultimately, the study demonstrates that introducing additional vaccine doses is not sufficient unless health systems ensure that eligible children actually receive them.

For Tanzania, closing the immunity gaps will require coordinated efforts among healthcare workers, parents, local authorities and immunisation stakeholders to make vaccination services accessible, reliable and effective.

Ensuring that children receive both doses remains central to reducing measles transmission, protecting vulnerable communities and preventing future outbreaks.