Optimizing one-dose and two-dose cholera vaccine allocation in outbreak settings: A modeling study

Abstract

Background A global stockpile of oral cholera vaccine (OCV) was established in 2013 for use in outbreak response and are licensed as two-dose regimens. Vaccine availability, however, remains limited. Previous studies have found that a single dose of OCV may provide substantial protection against cholera. Methods Using a mathematical model with two age groups paired with optimization algorithms, we determine the optimal vaccination strategy with one and two doses of vaccine to minimize cumulative overall infections, symptomatic infections, and deaths. We explore counterfactual vaccination scenarios in three distinct settings: Maela, the largest refugee camp in Thailand, with high in- and out-migration; N’Djamena, Chad, a densely populated region; and Haiti, where departments are connected by rivers and roads. Results Over the short term under limited vaccine supply, the optimal strategies for all objectives prioritize one dose to the older age group (over five years old), irrespective of setting and level of vaccination coverage. As more vaccine becomes available, it is optimal to administer a second dose for long-term protection. With enough vaccine to cover the whole population with one dose, the optimal strategies can avert up to 30% to 90% of deaths and 36% to 92% of symptomatic infections across the three settings over one year. The one-dose optimal strategies can avert 1.2 to 1.8 times as many cases and deaths compared to the standard two-dose strategy. Conclusions In an outbreak setting, speedy vaccination campaigns with a single dose of OCV is likely to avert more cases and deaths than a two-dose pro-rata campaign under a limited vaccine supply.

Evaluation of mpox vaccine dose-sparing strategies

“…Considering that as of the summer of 2022, the United States had secured 1.1 million of MVA vaccines and that there are an estimated 1.7 million people at high risk ( 11 ), our results suggest that dose-sparing strategies would outperform full-dose vaccination provided that the fractional dose retains at least 60% effectiveness of the full dose. These results are consistent with previous studies for other infectious diseases, such as cholera ( 12 , 13 ), influenza ( 14 , 15 ), and COVID-19 ( 16 ), which have found that dose-sparing strategies are optimal when the fractional-dose VE is around half as effective as the full dosage. The fewer the doses of MVA vaccine available, the projected payoff from using dose-sparing strategies increases.…”

Evaluating the use of dose-sparing vaccination strategies for Monkeypox

“…Considering that the US has secured 1.1 million of MVA vaccines and that there are an estimated 1.7 million people at high-risk 11 , our results suggest that dose-sparing strategies would outperform full-dose vaccination provided that the fractional-dose retains at least 40% effectiveness of the full-dose. These results are consistent with previous studies for other infectious diseases like cholera 12 13 , influenza 14, 15 and COVID-19 16 , that have found that dose-sparing strategies are optimal when the fractional-dose VE is around half as effective as the full dosage. The fewer the doses of MVA vaccine available, the projected payoff from using dose-sparing strategies increases.…”

Optimizing two-dose vaccine resource allocation to combat a pandemic in the context of limited supply: The case of COVID-19

“…For example, the well-known SEIR model, which considers the incubation period by means of introducing a compartment for exposed individuals, has drawn considerable attention (24). After that, the SEIR model and many of its variants were widely applied in studying the transmission of specific infectious diseases such as SARS (25-27), H1N1 (28)(29)(30), Smallpox (31)(32)(33), Ebola (34, 35), and Cholera (36,37). Currently, the classical SEIR model has also been used to model the recent outbreak of COVID-19 (38)(39)(40).…”

“…The significant challenge facing public health authorities is how to allocate scarce vaccines to mitigate the negative effects of a pandemic. This type of problem is referred to as vaccine allocation for epidemic control, and it has recently received widespread attention from the scientific community attention (37,47,(49)(50)(51)(52)(53)(54)(55)(56).…”

“…While these studies have provided valuable management insights regarding the vaccine allocation decisions in the context of an outbreak, they rely on the simplified assumption that the course of vaccination contains only single-dose. However, in the case of some infectious diseases (e.g., COVID-19, Cholera), most approved vaccines require two doses were administered at certain time intervals ( 6 , 37 ). Obviously, the two-doses vaccination procedure is more complex than the single-dose vaccination, which is often ignored in previous studies on the vaccine allocation optimization problem.…”