A root cause of this confusion may be that the CDC gives guidance based on the most up-to-date data, but not always on where this quickly evolving Covid-19 beast may be in the weeks ahead.
No one has a crystal ball, but it is possible to use sound public health principles of infectious disease epidemiology, human behavior in the face of risk, and societal responses to make reasonable estimates of how the pandemic might unfold next. Therefore, to prevent the spread of Covid-19, one has to tackle the areas where transmission is “substantial” or “high” right now (to use CDC’s classification terms) while predicting where it might move next and intervene with intensive prevention efforts there as well.
So, how can we look down the road as well as just outside the window?
First, we know about the “substantial” and “high” counties in the immediate, but we also know that “moderate” transmission counties could be on the brink of becoming the next hot spots. By the CDC’s definition, “moderate” counties have 10 to 49.99 new cases per 100,000 people in a one-week period and/or a positivity rate of 5% to 7.99% over the past 7 days. This is still a considerable amount of transmission.
Given the Delta variant’s contagiousness, we need to intervene in “moderate” counties before they get worse. Such worsening is not just theoretical; according to the CDC, on Monday the number of moderate transmission counties had shrunk by 12.58% in the past week, the number of “low” transmission counties had declined by 4.1% in the same time period, while substantial and high transmission counties had grown by 1.89% and 14.78% respectively.
As a New York resident, these numbers hit home for me. On July 27, as the CDC unveiled its updated guidance for fully vaccinated persons, there were 11 New York counties classified as substantial or high community transmission (most in New York City and surrounding areas); just a few days later, on Sunday, August 1, 2021, there were 33 substantial or high community transmission counties spread throughout much of the state.
The trend is going in the wrong direction. Given this real potential for a worsening situation in moderate counties across the nation, it is prudent to heavily promote vaccine use (our most important weapon against Covid-19) as well as temporary indoor mask use for all in those jurisdictions as well.
Second, the CDC’s publication on July 30, 2021, of data from Barnstable County, Massachusetts, shows that a jurisdiction can go from an average of 0 cases per 100,000 population per day to 177 cases per 100,000 population per day in just two weeks. In the CDC’s community transmission categorization that is going from “low” to “high” in just 14 days.
The Morbidity and Mortality Weekly Report (MMWR) shows that the Delta variant can spread incredibly rapidly even in an area with relatively high background vaccination rates and previously all but undetectable community transmission. Given this, it would seem that even in “low” transmission counties there should be promotion of vaccine use as well as temporary indoor mask use for all, regardless of vaccination status.
In addition to the promotion of vaccine use, we are seeing hints that the CDC may be warming to a more universal application of its updated mask guidance for fully vaccinated persons. In a slide deck obtained and reported on by The Washington Post, the CDC presents results of some mathematical modeling efforts that show that the use of non-pharmaceutical interventions (such as masks) can be a useful adjunct to vaccine uptake in disrupting Covid-19 transmission.
Indeed, the slide deck says, “(g)iven higher transmissibility and current vaccine coverage, universal masking is essential to reduce transmission of the Delta variant.”
Further, the MMWR about Barnstable County alludes to a possible expansion of the CDC’s updated guidance to broader areas: “Findings from this investigation suggest that even jurisdictions without substantial or high Covid-19 transmission might consider expanding prevention strategies, including masking in indoor public settings, regardless of vaccination status, given the potential risk of infection during attendance at large public gatherings that include travelers from many areas with differing levels of transmission.”
But the principle of making policy for tomorrow does not stop with these illustrations. For instance, the bedrock public health principles of disease elimination and eradication have taught us that we must accelerate across the finish line if we truly hope to control a disease.
In March, infectious disease expert and former federal official, Dr. Ronald Valdiserri, and I proposed six metrics that we felt should be met to control Covid-19 in the US by July 4. But, instead of making progress on the six measures, many states went backward on some key precautionary measures. If we are fortunate enough to momentarily find ourselves at a good place in the undulating pandemic, we can’t assume it will stay that way forever.
Of course, looking further down the epidemiological road carries some risk. There might be a pothole no one saw coming that the policy recommendation didn’t take into account. But not anticipating the future carries the risk of insufficiently preparing for downstream risks when we may have been able to prevent them in the first place.
To be clear, I support the CDC’s recently updated guidance for fully vaccinated persons, but we need to look a bit further down the road in our Covid-19 prevention policies.