As Pfizer and Moderna leap regulatory hurdles, how long will it be until vaccines allow for the U.S. to fully reopen?
By Will Rojas
Last month, Pfizer and Moderna released studies showing their respective vaccines were 90% and 95% effective. This past week, the FDA authorized the Moderna vaccine for emergency use, bringing both companies’ vaccines to market. With the arrival of mass vaccination in sight, a major question arises: when will the U.S. be able to fully reopen? The answer varies by state.
New York, California, and Florida have all made headlines with their unique approaches to combating COVID-19. New York, hit early in March, instituted a comprehensive lockdown while California later turned to more extreme measures and Florida kept relatively lax restrictions. With their diversity of techniques in combating COVID-19, they can serve as a benchmark for when other highly populated areas of the U.S. will reopen. A key tool to predict when this will happen is R.
R is the reproduction rate of the virus. For every person that gets COVID-19, there will be on average R additional people to whom it is transmitted. An R value above 1 means the population infected with the virus is growing, a value of 1 means the number of people infected is constant, and a value less than one means it is decreasing. A community is said to have reached herd immunity if enough of the population has been immunized so that R is one or lower. As a higher percentage of the population is immunized, the amount of people each infected person transmits the virus to (R) decreases in proportion, as that portion of the population is now immune to infection. As such, the percent of the population that needs to be immunized in order to reach herd immunity can be found by finding the percent change in R needed to reach 1 through observing the difference between R and 1 and dividing that number by R. This however assumes a 100% efficacy rate for the vaccine. Though many vaccine-makers have yet to release clinical trial data, Pfizer and Moderna have both reached at least a 90% efficacy rate, so we will assume a 90% rate for this analysis. Then, to find a more accurate required immunization rate for herd immunity, we must also divide by 0.9.
When analyzing R, it is important to note that it is not a constant number, but changes based on a myriad of factors. The current R levels in New York, California, and Florida are 1.22, 1.24, and 1.02, respectively. These rates are dependent on lockdown conditions. As such, they require 20%, 22%, and 2% of their population immunized, respectively, in order to halt the spread of the virus. However, if their lockdowns were lifted, R would change accordingly. Because of this, a more accurate R number for each state would be the rate before lockdowns were instituted. Major restrictions were not implemented until March 22 when Governor Cuomo of New York banned all non-essential businesses from operating in-person. Before this, in the two-week period preceding March 17, the R rates for New York, California, and Florida were 4.30, 3.16, and 3.08. Given this information, the percent of the population that needs to be immunized in order to stop the spread of the virus for each state is 85%, 76%, and 75%.
To determine the timeline for reopening, we first need to look at vaccine production and distribution expectations. On December 1, Operation Warp Speed chief Moncef Sloui predicted there will be 35-40 million Pfizer and Moderna doses available by the end of December, another 60-70 million available by the end of January, another 60-70 million as well as an additional 30-50 million from AstraZeneca and Johnson & Johnson available by the end of February, by March production would expand to a total of 150 million doses, and by the end of April and May, an additional 300 million doses would be manufactured. It is important to note that the Pfizer and Moderna vaccines require two doses, whereas the AstraZeneca and Johnson & Johnson only require one.
On November 24, the Department of Health and Human Services announced they would initially distribute vaccines based on the proportion of the U.S. adult population in each state. New York, California, and Florida have 6.04%, 12.00%, and 6.76% of the U.S. adult population. This means that there must be a total of 217,077,362 people vaccinated across the country for New York to reach herd immunity through vaccination, 193,911,352 for California, and 191,358,816 for Florida. If we take the lower expectation provided by Sloui, there will be enough doses to vaccinate 17.5 million people in December, 30 million in January, 60 million in February, and, if we assume March’s vaccine production is evenly split between one and two-dose deliveries, there will be an additional 112.5 million people vaccinated. With a total of 220 million people inoculated by the end of March, all three states should see an R level below one and a subsequent stable decline in cases.
Though cases may be on a steady path downwards by April, state opening guidelines are not entirely based on infection rate. New York allows for reopening if there is a decline in total hospitalizations, deaths, and new hospitalizations over a 14-day period and 30% of total hospital and ICU beds are available; California will lift restrictions when there is less than one new case per 100,000 people per day and testing positivity is less than 2%; Florida requires a downward trajectory of COVID-19 and flu-like illnesses, a downward trajectory of positive tests as a percent of total tests, and the capability for hospitals to treat all patients without initiating surge capacity along with a testing program in place for at-risk healthcare workers. Though not precisely aligned with a lower R value, these metrics (save for overall cases of flu-like symptoms and the establishment of a testing regimen) are all brought down by a lower reproduction rate, and though it is impossible to know when exactly these criteria will be met without knowing the number of COVID-19 cases and hospitalizations at a future point, the road to reopening begins in April. □
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