RMA has partnered with Oliver Wyman to make timely resources regarding the progress toward ending the pandemic available to members. RMA is hosting Oliver Wyman’s Pandemic Navigator on its website, and holding a series of webinars to help members utilize the Navigator to learn how scenarios will affect economic and business outcomes. Oliver Wyman is also contributing articles like this one to The RMA Journal and the RMA Industry Insider weekly email newsletter.
The Key to Getting Back to Normalcy: Cumulative Immunity
There is a lot of misleading and at times conflicting information regarding herd immunity, the latest vaccine trials, and the latest variants of the virus, and sometimes it seems impossible to see how these developments affect the questions we all are asking: When will the pandemic be over? When will we achieve herd immunity threshold? When can we go back to normalcy? (Albeit a new normal.) The answer is that it will occur after natural infections and vaccinations develop enough cumulative immunity in the population to naturally stop the virus from spreading exponentially without the aid of restrictions such as social-distancing and mask-wearing.
Cumulative population immunity is simply the sum of the population that:
- has already been infected and has protective immunity,
- is naturally immune to infection, or
- has been effectively vaccinated.
While medical studies reveal that a small percentage of the population may have pre-existing immunity, mediated by pre-existing long-memory T-cells, it is not possible to estimate the number of such people. Natural infections and vaccinations are the major contributors to cumulative population immunity, which is the focus of our analysis.
As of March 1, 2021, nearly a year into the pandemic, we estimate that roughly a quarter of the U.S. population has been infected by COVID-19. Our modeling reveals that, in addition to 29 million infections detected, there are roughly 50 million cases that are not detected. These undetected cases include people who were mostly asymptomatic and untested, false negatives, or did not get tested especially at the beginning of the pandemic when tests were not available.
Vaccinations have ramped up considerably since early December. The United States has ordered a combined 600 million doses of the Pfizer and Moderna vaccines. At its peak, the country has vaccinated at a rate exceeding 2 million people per day.
Willingness to get vaccinated among adults, an important factor as vaccination deployment continues, has also increased—to about 70% of U.S. adults. More good news: Johnson & Johnson’s one-dose vaccine was approved for the emergency use on February 28. However, as with natural infection totals, the vaccination progress is also uneven across the U.S. So far Alaska and West Virginia are leading the way in doses administered per population.
While there is significant debate on how much cumulative population immunity is needed from natural infections and vaccinations, our modeling reveals that the possible Herd Immunity Threshold (pHIT) lies somewhere in the 67% to 75% range. At that range, the effective reproduction rate of the virus without most restrictions will be equal to 1, and daily new cases will enter into a trend of systemic decline, other than some regional outbreaks. Based on the best existing estimates of COVID-19’s natural reproductive rate and assuming homogeneous transmission (equally infectious across the population), a traditional infectious disease model would say that the threshold is around 75%. However, SARS-CoV-2 appears to have a highly heterogeneous transmission, based on our behaviors. That means that the overall immunity threshold may be lowered. We may only need around 67% of the population to be immune through infections or vaccinations in order to start getting back to normalcy.
When will each state reach the herd immunity/protection threshold?
Total number of infections and vaccinations determine when we reach potential herd immunity threshold, where the population as a whole is more protected, assuming we confer immunity.
Oliver Wyman developed a 20 seconds long video about the timing of herd immunity threshold by state, available for RMA members at https://pandemicnavigator.oliverwyman.com/immunity
Unlike many models, Oliver Wyman’s Pandemic Navigator not only forecasts detected COVID-19 cases, but also estimates undetected COVID-19 cases historically and into the future. Oliver Wyman’s model also tracks and projects the number of effectively vaccinated individuals to date and in the future, respectively.