The Delta Dilemma: Loosening Covid-19 Controls At A Time Of Increased Danger

(Posted on Friday, July 16, 2021)

At a time when the United States and many other countries are beginning to lift restrictions, a new, more dangerous variant of SARS-CoV-2 has appeared that has prompted serious rethinking around what containment strategies should look like moving forward. The Delta variant is not only far more transmissible than its predecessors, but it appears to be more lethal to people of all ages as well. And it doesn’t look like vaccines will be the barrier that stops it.

When the Delta variant surged across India in March and April 2021, fomenting the conditions that pushed the country’s Covid-19 death toll past 400,000 (now estimated to be two million), we knew little about how it compared to preceding strains—only that where it went, havoc followed. Today, the Delta variant has spread to more than 100 countries and become the dominant strain in most, including, as of last week, the United States. Not only is the risk of death from Delta twice as high, it is so transmissible that outbreaks in Australia have been traced back to moments of “scarily fleeting” contact. These characteristics don’t just demand caution, but a reevaluation of current public health policy.

What we have going for us are the mRNA vaccines. Against Delta’s predecessors they perform almost immaculately, with a two-dose regimen preventing nearly all infection, disease, and death in those who received it. But the Delta variant, according to data from Israel (where 80 percent of adults are fully vaccinated), has proven a more challenging immunization target. While the Pfizer vaccine protected 93 percent of immunized Israelis from hospitalization and death, nearly 40 percent were still vulnerable to infection. The British government reported that for symptomatic infection, that rate was about 12 percent. And a recently published study, conducted through May and June in Guangzhou, China, begins to illustrate why.

The study gathered viral samples from 62 Covid-19 patients who were infected during the first Delta outbreak in mainland China and cross-analyzed them with those of 63 individuals infected in 2020 with a prior strain. It focused on two epidemiological parameters that, when it comes to determining infectivity, are particularly telling. The first is viral load, or the amount of virus particles replicating in the respiratory tract. The second is the amount of time that elapses between the moment of exposure to the moment of detection via PCR or antigen test.

On both fronts the findings were startling. The viral load of patients infected with the Delta variant was about 1,000 times as high. And on average, it took four days for viral titers in these patients to replicate to detectable levels—a full 48 hours sooner than last year’s strain. Data analyst Tomas Pueyo, who also referenced the Gunagzhou study in his most recent article, compared the R naught (R0) values—a mathematical measure of contagion—of the Delta and original variants. His comparative model, which placed the R0 of the original strain at 2.7 and that of Delta at 6, shows a similarly exponential rise. Evidently the difference in transmissibility isn’t just a matter of percentage points, as was the case with the Alpha variant, but orders of magnitude.

The change in viral dynamics is drastic enough to necessitate a corresponding shift in pandemic controls. Only through a rigorous, large-scale testing and tracing program could Chinese health officials obtain data granular enough for the purposes of the Guangzhou study. That same infrastructure allowed them to implement policy changes proportional to the increase in infectivity. When outbreaks intermittently sent Guangzhou into lockdown in 2020, travelers using public transport to leave the city were required to submit negative Covid-19 test results within seven days of their departure. As of June 7, the local government has shortened the time window to just 48 hours—a rapid turnaround, to be sure, but befitting in its urgency. Travelers arriving in China now have to quarantine for three weeks due to increased reports of delayed or long-lasting effects.

The policies of most other countries, however, haven’t budged an inch, especially in places where vaccines have gradually displaced other public health measures as the primary containment strategy. In the United States, the genomic sequencing efforts so critical to tracking and curbing the spread of new variants remain slow and encumbered. Last month the US government committed billions of dollars to antiviral Covid-19 drug development, but none of the treatments to emerge in the past year and a half have proved deployable at scale. And as vaccination rates climb and stall, safety measures like masks and social distancing are falling out of fashion. All this despite the fact that in the United Kingdom, another country where more than half the population is vaccinated, infections are once again on the rise.

As incredible as the mRNA vaccines may be, placing too many eggs in the same basket never ends well. Every tool we have at our disposal—testing, tracing, surveillance, cooperation—we must put to work. Every drug or vaccine candidate that shows promise, we must finance and bring to fruition. This multilayered strategy, which I call multimodal therapy, may be the only way to seal all the cracks that the Delta variant and its successors will exploit.

Ultimately, the success of multimodal therapy depends on the cooperation of scientists, researchers, and vaccine and drug manufacturers around the world. In the face of the Delta variant, no country—no matter the rate of vaccinations or duration of border controls—can possibly remain an island. We have no time to waste before the next more transmissible and even more virulent variant appears. It may already be circulating in the form of the Delta plus or Lambda variants.

Read full article on Forbes

Originally published on Forbes (July 13, 2021)