As policymakers decide about typhoid conjugate vaccine (TCV) introduction into their immunization programs, understanding how the COVID-19 pandemic affected enteric fever surveillance provides critical context for burden data. The latest findings from the Surveillance for Enteric Fever in Asia Project (SEAP), published in The Lancet Regional Health – Southeast Asia, provide valuable insights into how pandemic-related disruptions impacted enteric fever burden in Bangladesh, Nepal, and Pakistan. The study used blood culture surveillance for Salmonella enterica serotypes Typhi (S. Typhi) and Paratyphi (S. Paratyphi) to generate evidence to help guide prevention and control strategies in these countries. “Enteric fever” includes typhoid and paratyphoid, yet existing vaccines protect only against typhoid. However, water, sanitation, and hygiene policies and programs will impact both typhoid and paratyphoid, making this a strong indicator for policy considerations.
Pandemic disruptions and rebound cases
The study reports data from 2019 to 2022, a timeframe that significantly overlaps with the COVID-19 pandemic. Despite this unprecedented challenge, SEAP teams continued enteric disease surveillance across hospital and laboratory network sites in Dhaka, Bangladesh; Kathmandu and Kavrepalanchok, Nepal; and Karachi, Pakistan. Teams collected information on enteric fever severity, burden, and drug resistance.
In all three countries, cases identified through enteric fever surveillance dropped significantly during the first year of the pandemic. This drop was likely related to multiple factors, including changes in care-seeking, lockdowns, and health facility processes. The reduction may also reflect a temporary decline in transmission due to improved public health measures, such as handwashing and social distancing.
By mid-2022, cases across the three countries largely returned to pre-pandemic levels, highlighting a critical point: typhoid and paratyphoid remain persistent threats. Pakistan reported the highest number of confirmed cases across the three countries between 2019-2022. In November 2019, Pakistan started TCV introduction with a mass campaign in urban areas of Sindh Province and completed a phased nationwide rollout in 2022. The study, whose facilities were located in Karachi, observed a large burden of typhoid in children who were age-eligible for TCV but reported not receiving the vaccine, which underscores the need for continued surveillance and strengthening the reach of routine vaccination programs. The Pakistani Government conducted a TCV campaign in Sindh Province in 2024 to reach children who remained unvaccinated against typhoid. In Bangladesh, after the initial decline, cases increased to pre-pandemic levels and remained consistently high, underscoring the country’s continued vulnerability. Bangladesh plans to introduce TCV into their routine immunization program. In contrast to Bangladesh and Pakistan, cases of enteric fever identified through surveillance activities remained very low in Nepal throughout the study period, even prior to TCV introduction in April 2022. This contrasts with other data showing a high typhoid burden in Nepal. The discrepancy between low case counts in SEAP surveillance and higher burden estimates from other sources highlights the difficulties of accurately measuring typhoid burden through surveillance.
Disease severity
In the study, illness severity was reported by laboratory-confirmed enteric fever cases requiring hospitalization and the number of deaths reported. Hospitalization rates across the three countries were similar (33% in Pakistan, 27% in Bangladesh, and 28% in Nepal), showing that many patients experienced symptoms or complications serious enough to require inpatient care. Six patients with culture-confirmed typhoid died in Bangladesh and Pakistan; the median age of those who died was 1.2 years, highlighting the heightened vulnerability of young children to typhoid.
The ongoing threat of drug resistance
In addition to burden and severity, the study reported data on drug resistance. Drug resistance, where certain antibiotics no longer treat an infection, remains a major concern in the treatment of enteric fever, particularly in Pakistan, where extensively drug-resistant typhoid strains continue to circulate. Across the three sites, most patients had typhoid or paratyphoid that was resistant or non-susceptible to at least one antibiotic. These data reinforce the urgency of integrating TCVs into national immunization programs, not only to reduce disease burden but also to curb reliance on antibiotics and help reduce the further evolution of drug resistance.
Lessons for future disease monitoring
The experience of continuing enteric fever surveillance during the COVID-19 pandemic also offers important lessons for the future of disease monitoring. SEAP demonstrated that adaptable surveillance can continue to generate data despite a major health system crisis. Investing in laboratory capacity, data systems, and cross-country collaboration proved essential in maintaining operations and ensuring data quality during an otherwise disruptive period.
As the global health community refocuses on routine immunization and pandemic recovery, SEAP’s findings serve as an important reminder—sustained surveillance and strong TCV programs with high-coverage and equitable access are essential to the control and prevention of typhoid.
Cover photo: Child photographed during Nepal’s TCV campaign. Credit: TyVAC/Rocky Prajapati
