Supply vs Demand: When Will the Scales Tip on COVID-19 Vaccination in the U.S?

For months, the biggest challenge in introducing COVID-19 vaccines in the US was that demand far exceeded supply. In fact, limited supplies coupled with restricted eligibility in many parts of the country meant that most people could not be vaccinated when they wanted. Now that supply has grown significantly and eligibility is fully open to adults in all states starting April 19th, the main question is when will supply exceed demand. While timing can vary from state to state, we estimate that in the United States as a whole, we will reach a tipping point in the vaccination craze in the next 2-4 weeks. Once that happens, efforts to promote vaccination become much more difficult and challenging to achieve the level of herd immunity that is likely to be needed.

Our surveys and others have shown that the proportion of adults who have either received a dose of vaccine or want to get vaccinated as soon as possible has increased steadily. On March 21, it was 61% (compared to 55% in the previous month). This increase reflects a shift from those who say they want to wait and see to the vaccination enthusiast group. In fact, the proportion who say they want to “wait and see” has steadily decreased as more and more people are excited about the vaccination.

If we use 61% as the current “outer edge” of vaccination enthusiasm, that translates to roughly 157 million adults. The latest data from the CDC shows that nearly 131 million adults (or 50.7% of all adults) had received at least one vaccine dose by April 19. That leaves another 27 million adults before we hit the “excitement” line. "At the current rate of first doses per day (using a 7-day moving average from April 13th) – or about 1.7 million a day – we would hit the tipping point in about 15 days. If the pace of vaccination accelerates, it could of course be sooner. However, if those who say they want to be vaccinated immediately face challenges in accessing vaccinations this can take longer.

Estimated number of days it will take to reach all adults in the US who want a vaccine of at least one dose, as of April 19, 2021

We also know that over time, people have switched from the “wait and see” group to the vaccination enthusiast group, suggesting that the 61% may be a floor, not a ceiling. If around a third of the “wait and see” group switched to the enthusiasm group (comparable to what happened last month), the “outer edge” of enthusiasm for vaccination would increase to 170 million people (or 66% of all adults). At the current rate of daily vaccine doses, it would take 22 days to reach the point where supply exceeds demand. If half of the "wait and see" group moved, it would take about 28 days to reach the turning point.

So, on average for the country, we seem pretty close to the tipping point where the demand for vaccines rather than the supply of vaccines is our greatest challenge. Federal, state and local officials as well as the private sector are faced with the challenge of figuring out how to increase the willingness to vaccinate those who are still on the fence and, ideally, a fifth of adults who have consistently stated that they would not be vaccinated or would only do so if necessary. Now that supply has increased and eligibility has expanded, it will take a concerted effort to achieve adequate levels of herd immunity vaccination in a way that also meets equity goals.