The Delta variant of COVID-19 is rightfully all over the news as it quickly becomes the predominant strain of the virus worldwide due to its higher infectivity. Delta is estimated to be 50% more infective than the predominant strain of COVID-19, which was already 50% more infective than the original strain. What this means is that previously each person with coronavirus might have infected two other people; in contrast, someone with Delta might infect three or four other people.
As with all things COVID-19, there are many unanswered questions related to the Delta variant. For example, the data can’t yet answer whether the Delta variant is more likely to make people seriously ill than other variants. One early study out of England and Scotland may indicate this is the case, but more research is clearly needed. One thing is clear, cases and hospitalizations are overwhelmingly in the unvaccinated.
One concern foremost on our minds is whether vaccines provide similar levels of protection against the Delta variant when compared to earlier strains of the virus. You’ll recall that we (following advice from CDC) followed the science of the effectiveness of the vaccines and strongly recommended not doing any testing on staff or campers who are fully vaccinated– even if they have been exposed to someone who has tested positive for COVID-19. But breakthrough infections, an infection in someone who has been vaccinated are a growing concern with the Delta variant.
Breakthrough infection is perhaps less concerning than breakthrough illness, however. Some early data suggest that while the vaccines may be just as effective in preventing serious illness due to the Delta variant, they may be less effective at preventing asymptomatic or mild illness. For example, one studyout of Israel reported that the Pfizer vaccine was only 64% effective in preventing any infection by the coronavirus (though it maintained a 93% rate of efficacy in preventing serious illness). A different report from England found that the Pfizer vaccine was 88% effective at preventing any symptomatic illness due to the Delta variant in contrast to its 93% efficacy against the previously dominant strain.
Previous research has shown that people who are asymptomatic with virus are less likely to transmit the virus than people with symptoms or who go on to develop symptoms. This does provide us with some reassurance that vaccinated people who are infected with the Delta variant asymptomatically may help stop the spread of the virus to others.
Does this change our recommendation about not testing vaccinated people who are asymptomatic? Read On….