As something resembling normal life resumes in the United States, many Americans are wondering how concerned they should be about the delta variant of the coronavirus. Reports from Britain and Israel suggest that this mutation is more contagious than previous versions of the virus, and it is already on the rise in this country. But there is good news: The vaccines work against this frightening new variant, and they remain our best, most powerful tool to extinguish the pandemic here and worldwide.
First, it’s important to understand how this version of the virus arose. The coronavirus can mutate when it replicates, especially when circulating at high rates. There have been different variants of concern, starting with the alpha variant, which was prevalent in the United States in the spring. But the delta variant, which was first detected in India this year, is now the most common version in our country.
The reason it has so quickly dominated is that it is more “fit” than other variants — outcompeting them when it comes to reaching and infecting unvaccinated people. Although this means delta is more easily transmitted than the other variants, there is no evidence that it causes more severe illness. It has not resulted in higher rates of hospitalization among the infected, and it is not resistant to a full course of vaccines.
How do we know that delta is not vaccine resistant? All three vaccines authorized in the United States (Pfizer, Moderna and Johnson & Johnson) have been shown in clinical studies to produce strong neutralizing antibody responses against the variants. A report published Thursday in the journal Nature showed that people who received both shots of the two-dose vaccines retained significant protection against the delta variant.
The Pfizer and Moderna vaccines are also known to spark the creation of “memory B cells,” which can quickly produce antibodies in the future if they encounter the virus again and can even adapt to its variants. The vaccines also prompt the creation of “T cells,” which protect us against severe disease. Data from La Jolla Institute for Immunology and the University of California at San Francisco (UCSF) show that the T cell response from the vaccines is strong across all the variants. Real-world data also shows that vaccines are extremely effective in staving off serious illness from the delta variant, preventing more than 90 percent of hospitalizations in England. If vaccinated people come down with symptomatic covid-19 triggered by the delta variant, it is most often a mild infection.
Still, the variant has sparked understandable concern. In countries with high rates of vaccination — including Israel, Britain, the United States and Canada — cases have gone up among the unvaccinated as the delta variant has taken hold. There have also been some well-publicized examples of breakthrough infections among vaccinated people. Israel’s Health Ministry said this month that the Pfizer vaccine appears to be just 64 percent effective in preventing symptomatic illness from the delta variant. But much larger data sets from Singapore, Canada and Britain show that the vaccines are 80 to 90 percent effective against symptomatic infection and even more effective at preventing severe disease.
Some of the increases in cases among the vaccinated are simply an artifact of testing. Places that still use polymerase chain reaction (PCR) tests as the gold standard do not yet incorporate the “cycle threshold” in their test results. The cycle threshold value tells you how many cycles the PCR machine must go through to trigger a positive result. A high CT value (more than 30 cycles) means the viral load in the nose is very low and most likely noninfectious. Experts at UCSF and elsewhere have cautioned against using PCR tests without CT values, and the Centers for Disease Control and Prevention does not recommend testing asymptomatic people after vaccination. But the practice continues, and many of the recent cases in Britain and Israel were diagnosed via PCR tests among asymptomatic vaccinated individuals. A low, noninfectious viral load in the nose of an asymptomatic person is probably a sign of the success of the vaccines, since antibodies and T cells from the vaccines cluster in the nose to fight infection and kill the virus. Dead virus can still be picked up by a PCR test.
Early in the pandemic, a spike in case counts was quickly followed by a rise in hospitalizations and deaths. That is no longer the case in highly vaccinated countries, where case counts are increasingly uncoupled from hospitalizations. In Britain, for instance, public health officials are now carefully tracking hospitalizations instead of cases. However, we are seeing increasing hospitalizations in places with low vaccination rates. That is why I have argued that ensuring every country has access to vaccines is the most pressing moral and ethical problem of our day.
Yes, the variant means there will be isolated outbreaks and some places will ask residents to put their masks back on. But we are moving in the right direction in the United States, and we should not let fear of the new variant discourage us. Case rates, hospitalizations and deaths have fallen dramatically in highly vaccinated areas, and more than 67 percent of adults have received at least one dose. Our plentiful vaccines mean that every death from covid-19 is preventable, including deaths caused by the delta variant. Now is the time to redouble our efforts to get all eligible people vaccinated and stamp out the pandemic. Whatever we can do — with compassion and education — to increase vaccine uptake in this country and disseminate vaccines worldwide is imperative under this new threat.