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.
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—we must put to work against the new and dangerous Delta variant.
www.forbes.com