publications

2024

1. medRxiv

   Immune history influences SARS-CoV-2 booster impacts: the role of efficacy and redundancy

   Sophie L. Larsen, Iffat Noor, Haylee West, Eliana Chandra, Pamela P. Martinez, and Alicia NM Kraay

   medRxiv, 2024

   Abstract PDF

   Given the continued emergence of SARS-CoV-2 variants of concern as well as unprecedented vaccine development, it is crucial to understand the effect of the updated vaccine formulations at the population level. While bivalent formulations have higher efficacy in vaccine trials, translating these findings to real-world effectiveness is challenging due to the diversity in immune history, especially in settings with a high degree of natural immunity. Known socioeconomic disparities in key metrics such as vaccine coverage, social distancing, and access to healthcare have likely shaped the development and distribution of this immune landscape. Yet little has been done to investigate the impact of booster formulation in the context of host heterogeneity. Using two complementary mathematical models that capture host demographics and immune histories over time, we investigated the potential impacts of bivalent and monovalent boosters in low– and middle-income countries (LMICs). These models allowed us to test the role of natural immunity and cross-protection in determining the optimal booster strategy. Our results show that to avert deaths from a new variant in populations with high immune history, it is more important that a booster is implemented than which booster is implemented (bivalent vs. monovalent). However, in populations with low preexisting immunity, bivalent boosters can become optimal. These findings suggest that for many LMICs – where acquiring a new vaccine stock may be economically prohibitive – monovalent boosters can still be implemented as long as pre-existing immunity is high.

2. RSPB

   Transparent transmission models for informing public health policy: the role of trust and generalizability

   Sophie L. Larsen, and Alicia NM Kraay

   Proceedings of the Royal Society B, 2024

   PDF

2023

1. SciAdv

   Quantifying the impact of SARS-CoV-2 temporal vaccination trends and disparities on disease control

   Sophie L. Larsen, Ikgyu Shin, Jefrin Joseph, Haylee West, Rafael Anorga, Gonzalo E. Mena, Ayesha S. Mahmud, and Pamela P. Martinez

   Science Advances, 2023

   Abstract PDF

   SARS-CoV-2 vaccines have been distributed at unprecedented speed. Still, little is known about temporal vaccination trends, their association with socioeconomic inequality, and their consequences for disease control. Using data from 161 countries/territories and 58 states, we examined vaccination rates across high and low socioeconomic status (SES), showing that disparities in coverage exist at national and subnational levels. We also identified two distinct vaccination trends: a rapid initial rollout, quickly reaching a plateau, or sigmoidal and slow to begin. Informed by these patterns, we implemented an SES-stratified mechanistic model, finding profound differences in mortality and incidence across these two vaccination types. Timing of initial rollout affects disease outcomes more substantially than final coverage or degree of SES disparity. Unexpectedly, timing is not associated with wealth inequality or GDP per capita. While socioeconomic disparity should be addressed, accelerating initial rollout for all over focusing on increasing coverage is an accessible intervention that could minimize the burden of disease across socioeconomic groups. Speeding up vaccine rollout for all socioeconomic groups surpasses the impact of eliminating disparity or increasing coverage.