What do you mean by vaccine equity? And why does it matter for population health? This is the question that I’ve been asked all week. Here’s a short explanation:

Thanks to @sdbaral for expert input and insights.

Let’s start with the goals of #covid19 vaccination. From a public health perspective, we want to reduce #covid19 hospitalizations and deaths.

From a societal perspective, we also want to ensure the continuity of other vital institutions, including schools; limit secondary social and economic impacts, and mitigate other inequities, including racial disparities.

It’s worth noting that #covid19 vaccination is not a reward for positive behavior, health status, social standing, or other factors. It is not also a tool for remediating other structural drivers of health or social inequities, such as poor housing or employment conditions.

From a public health perspective, we are primarily interested in three things 1) #covid19 exposure (risk of infection) 2) transmission (risk of spreading to others) and 3) disease (risk of severe illness or death). Let’s call 1+2 social vulnerability, 3 medical vulnerability.

We often focus on medically vulnerable populations—those more likely to experience severe illness or death. Medically vulnerable populations include the elderly (65+) and those with underlying illness that put them at greater risk of death or severe illness.

We talk less often about socially vulnerable populations though, or those who are more likely to be exposed or transmit to others. What increases risks of exposure/transmission most? Primarily employment and housing conditions and things associated with that (transportation).

We can see that while some may be medically vulnerable, they may be at much lower risk of exposure (and transmission to others). Conversely, younger, healthier people are generally at increased risk of infection & transmission to medically vulnerable people.

COVID-19 medical and social vulnerability fall along a spectrum. Not all essential workers have equal workplace exposures, and not all medically vulnerable populations have equal risk of severe illness or death.

COVID-19 disparities at individual and population level reflect a combination of increased risk of infection, transmission, and severe illness and death. We see the worst outcomes when significant medical and social vulnerability overlay closely.

The devastating outcomes we see in nursing homes reflect the convergence of medical and social vulnerability. Low paid workers from high burden communities serving one (and often more) medically fragile populations in a congregate living setting.

What does this mean for vaccination? We want to allocate scarce resources to groups whose disproportionate risks of infection, transmission, and severe illness contribute most to the #covid19 hospitalizations and deaths that we are seeing at population level.

Most understand why we would prioritize medically vulnerable populations—those 65+ (16% of infections, 80% of deaths in US). Many do not understand why we would consider prioritizing younger populations, including the essential workforce.

What does the data tell us? The analysis ACIP used found that vaccinating 65+ first resulted in slightly fewer deaths (1-4%) and younger populations (including essential workforce) resulted in slightly fewer infections (1-5%).
https://www.cdc.gov/vaccines/acip/meetings/downloads/slides-2020-10/COVID-Biggerstaff.pdf

One major source of uncertainty though is the lack of knowledge on whether #covid19 vaccination will protect against transmission--and if it will shift this balance. Absent that data, it’s still important to understand the critical role transmission plays in driving disparities.

Achieving equity is not just an academic exercise—it requires delivering vaccines to vulnerable populations, some which may be harder to reach. More resources are required to this—but these efforts should have greater population impact.

There’s a huge rush to get shots in arms. Inequitable vaccine allocation will limit the effectiveness of scarce resources though. Directing resources to groups that have lower risk of infection, transmission, and death will result in less impact at population level

There may be other reasons why we might want to prioritize groups, such as teachers, that align with broader issues of social equity, even if these groups are not among the most medically or socially vulnerable.

What’s the larger lesson? Achieving health equity requires allocating disproportionate resources to groups with disproportionate risk or burdens. Equitable allocation is aligned with public health goals—prioritizing vulnerable populations yields impact at population level.

Adding an interview that nicely describes some of the ethical and practical considerations that ACIP and states are trying to balance in thinking about vaccine allocation. https://www.newyorker.com/news/q-and-a/deciding-who-should-be-vaccinated-first

Adding a link to this great thread from Dr. @celinegounder that highlights the critical importance of delivery, and not just prioritization, in achieving vaccine equity. https://twitter.com/celinegounder/status/1350895557833879553

And one more article from @zeynep on the critical importance of eliminating barriers to access to #covid19 vaccines. https://www.nytimes.com/2021/01/15/opinion/coronavirus-vaccine.html