How many doses of Covid-19 vaccine are needed to protect front-line health workers and people at higher-risk of severe or critical Covid-19 disease?

The race for Covid-19 vaccines is well underway. As is the thinking on how to allocate what will be a limited supply for the first many years of production.

The current model of vaccine distribution primarily relies on a new vaccine being launched in high income countries and once scaled, becoming available to low- and middle- income countries. A key part of the mission of Gavi, the Vaccine Alliance, is to positively disrupt this delay and drive earlier access for children in lower resourced countries. Including where burden of disease is often higher.

In a global pandemic, the world is thinking through what equitable distribution of Covid-19 vaccine could look like. The “Access to Covid-19 Tools ACT Accelerator” launched on 24 April by 40 countries and funded with $8 billion aims to achieve exactly that - the accelerated development, production and equitable access to new Covid-19 vaccines, therapies and diagnostics.

While the work on allocation principles continues, we modelled an allocation of Covid-19 vaccine that starts with protecting front-line health workers and people who are higher-risk of developing severe or critical disease. This is based on published analysis of hospitalizations and deaths at the time. As this may change, including due to differences in underlying disease, the main point is to prioritize on the basis of health, with the best information available at the time.

Representing nearly 80% of Covid-19 deaths, one of the most vulnerable groups is the 728 million people who are over the age of 65. The other vulnerable group is people with underlying health conditions that increases the risk of severe or critical Covid-19, including hypertension, obesity, diabetes, heart disease and asthma. In the U.S., 88% of Covid-19 patients hospitalized had more than one these underlying condition (per U.S. CDC as compiled by TIME). Given the overlap of conditions, the limited information on severity of a condition, and because at 1.15 billion it is the underlying condition held by the largest number of people -  we have used hypertension as the proxy for all underlying conditions. To avoid double counting, we removed the number of people with hypertension that are over the age of 65, resulting in 880 million people. When we add in the 52 million health workers globally, and the elderly,the total number of people to vaccinate first is 1.66 billion. (Note, this number does not include non-health, front-line workers. Analysis to get this quantification is still underway.)

This targeting of ‘people at higher-risk and front-line workers first’ model would result in North America having 38% of their population immunized; Europe with 28%; Central and South America and the Caribbean with 23%; Asia and Oceana with 21%; and Africa with 15%.

Of the 1.66 billion people targeted, 58% would be in Asia and Oceana, 12% in the Europe, 12%in Africa, 9% in Central and South America and the Caribbean, and 9% in North America.

A closer look at the breakdown by region shows how a larger proportion of people designated as higher risk and health workers (H+>65+HW) impacts the proportion targeted. An allocation with health as the overriding objective should do just that.

• 969 million of the 1.66 billion people targeted first via this model are in Asia and Oceana, which includes China, India and Oceana. This is by far the most populous region and is home to 60% of the world’s people. The H+>65+HW is equivalent to 21% of their population – the second lowest proportion of the regions.
• 206 million people targeted first are in Europe, the third most populous region and the second highest H+>65+HW proportion at 28%.
• 195 million people targeted first are in Africa. Africa is the second largest region in terms of population, but has the lowest H+>65+HW proportion at 15% of the population.
• 148 million people targeted first are in Central and South America and the Caribbean that has a H+>65+HW proportion of 23%.
• 141 million people targeted first are in North America, which is the smallest region in terms of population at 5%. However, the H+>65+HW proportion is the highest at 38%.

As most vaccines require multiple doses in order to provide sufficient protection, if we assume a two-dose vaccination schedule, approximately 3.3 billion doses would be needed to protect the most vulnerable and front-line health workers. Unless of course a booster dose is needed. Or if the virus mutates at a rate and significance similar to the influenza virus which would mean more frequent vaccination.

The world will continue to learn more about the SARS-CoV-2 virus, Covid-19 disease, our vulnerabilities, and the characteristics of the vaccines being developed. An allocation scenario will be refined, debated and different scenarios will be developed. But at this point, within a likely overall goal of immunizing all 7.8 billion of us, and then the 130 million babies born each year, this model gives us an example quantification of the number of people to get access first, while more sophisticated principles are being developed.

It also underscores the importance of health needs be the driving factor of any allocation.

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