COVID-19 vaccine effectiveness to be affected heavily by infrastructure, public attitudes

Billions of dollars have been spent on developing COVID-19 vaccines, and preliminary evidence suggests that several candidates appear to be extraordinarily effective. "But there are lots of ways to think about the effectiveness of a vaccine," says Walensky. She teamed up with A. David Paltiel, PhD, a professor of Public Health (Health Policy) at the Yale School of Public Health (YSPH), and several other colleagues to create a mathematical model that assessed how other factors beyond a COVID-19 vaccine's efficacy might influence how well it thwarts the disease. Those factors included:

• How fast and broadly can the vaccine be produced and administered? Some candidate vaccines pose logistical challenges, such as needing to be stored in ultra-cold freezers or requiring two doses, spaced weeks apart.
• What portion of the population is willing to be vaccinated? National surveys suggest that as few as 50% of Americans say they will receive a COVID-19 vaccine.
• The severity of the pandemic when a vaccine is rolled out. The proportion of infections a vaccine is able to avert is directly related to the public's willingness to engage in mitigation behaviors, such as wearing masks and social distancing.

The mathematical model considered how these factors would influence the impact of vaccines of varying levels of efficacy. "We found that infrastructure will contribute at least as much to the success of the vaccination program as will the vaccine itself," says Paltiel. "The population benefits of vaccination will decline rapidly in the face of manufacturing or deployment delays, significant vaccine hesitancy, or greater epidemic severity."

To help ensure a vaccination program's success, Walensky says that significantly greater investment is needed in an infrastructure to deliver COVID-19 vaccines. Moreover, powerful public messages and on-the-ground implementation strategies at the local level are also necessary to help overcome skepticism about vaccines, especially in underserved populations.

Likewise, the Health Affairs study showed that even a highly effective vaccine will struggle to control COVID-19 if infection rates continue to rise. "If I have a cup of water, I can put out a stove fire. But I can't put out a forest fire, even if that water is 100% potent," says Walensky, emphasizing the public's role in keeping the infection rate low by mask wearing and social distancing. "We'll get out of this faster if you give the vaccine less work to do."

Walensky is also co-director of the Medical Practice Evaluation Center at MGH and a professor of Medicine at Harvard Medical School (HMS). Paltiel is also professor of Management, professor in the Institution for Social and Policy Studies, and co-director of the Public Health Modeling Concentration at Yale. Coauthors of the study were Jason L. Schwartz, PhD, assistant professor of Public Health (Health Policy) at YSPH; and Amy Zheng, a medical student at HMS.