The 5/7 number you post (715,000) is the number of first dosages
on May 7, not the "7 day rolling average". Per the CDC, the 7-day moving average on May 7 was 650,964. Please refer to the following chart from the
CDC:
View attachment 557038
Depending on the day of the week, there is a great deal of variance. Therefore, you should look at this in whole week increments.
The most recent day that the CDC reported a moving average is May 7. I'll use that as the end date, and count backwards week-by-week.
This results in the following 7-day moving averages as reported by the CDC (with percent drop from previous week), for those receiving a
first dose:
- April 9: 1,831,161
- April 16: 1,547,994 (15.5% drop)
- April 23: 1,134,806 (26.7% drop)
- April 30: 918,792 (19.0% drop)
- May 7: 650,964 (29.1% drop)
As you note, we need to focus on those receiving first doses. This tells us how many
additional people are being vaccinated per day, on average, for that week.
As you suggest, second doses are a trailing indicator and will lag behind those receiving first doses. For example, for the week of April 16, the 7-day moving average was 1,547,994 receiving a first dose each day. This is significantly more than those receiving a first dose for the week of May 7. Chances are, there were more people receiving a
second dose for the week of May 7 than who received a first dose for that same week.
From April 9 to May 7, we've gone from a daily
first dose average of 1,831,161 to 650,964. Together, these two numbers tell us the decline in first doses over this timespan.
For those interested where this data is coming from, I encourage you to visit the below CDC page and then filter on "People Receiving Dose 1".
https://covid.cdc.gov/covid-data-tracker/#vaccination-trends