The latest Delta Variant is much more infectious than the original: they estimate an Ro of 5-9, vs. the 2-3 for the original, which makes Delta “as transmissible as chickenpox.” We’ve been estimating Ro of ~6 for Delta, or ~2x as infectious as the original. It may be a bit worse than that.
As we learned in the CDC announcement 2 days ago, they’re finding equal viral loads in noses/mouths of people with breakthrough infections as in infected unvaxxed people. Likely means that breakthrough cases can spread the virus more readily than we previously thought. Chair, UCSF Dept of Medicine, Career Bob Wachter told in his tweer.
He was responding to a report in CDC document on Delta Variant.
New Delta Variant what we need to know
Vaccine efficacy: several estimates; they tend to show ~80% efficacy vs. Delta (vs. the prior 95%). Thankfully vax IS still ~95% effective vs. serious infections. That the efficacy of the vaccines is holding up for serious infections is the main piece of good news here.
Lower efficacy in selected populations: significantly lower efficacy (~70%) in the nursing home elderly (Fig L) and in immunocompromised (Fig R) patients. These are likely to be the first groups made eligible for boosters. Hopefully soon.
Waning of immunity: no new data here (that I saw) supporting Pfizer’s findings that mRNA efficacy wanes over time. But the final bullet says protection from prior infection wanes after 6 months – adding to risk to those whose immunity was from prior Covid. They still need vax.
The seriousness of Delta infections. Early UK/India studies pointed to more serious infections, then consensus seems to be that they were not more serious. This document supports the “more serious” stance. That’s concerning.
Notwithstanding all the noise about breakthrough infections, the case for vaccination remains enormously strong: they show an 8-fold reduction in cases, and a 25-fold reduction in hospitalizations and deaths with vaccination.
That said, as more people are vaccinated, there’ll be more people in hospital and more dying w/ breakthrough infections (even though vaccines work! – it’s just math). Estimate here: 9% of hospitalized pts & 15% of deaths in vaxxed pts. Seems a little high, need to confirm.
To block the spread of Delta – a more infectious, and possibly more serious virus – particularly if it’s true that vaccinated folks can be part of the chain of spread
