Last spring, my Advisory Board colleagues and I were optimistic that the United States could be trending toward a "good" outcome in the Covid-19 pandemic. But now, the delta variant is coursing through the country. And if you’re anything like me, you're probably asking yourself just how worried we should be. When will we hit a peak and see hospitalizations—which are on the rise in many parts of the country—decline? Amid the constant headlines of case numbers, vaccine efficacy, mask mandates, and other Covid-19 news, I think it's crucial to step back and ask: What factors really matter?
Let's be very specific about which factors we should be following—and which we should deprioritize. Below, I’ve identified seven factors to pay close attention to and two factors that may be more distracting than helpful.
7 factors to watch amid the delta surge
1. The transmissibility of the delta variant in the United States
One of the most striking factors underlying the delta surge is its heightened transmissibility—this is the most transmissible Covid-19 variant we have seen yet. The delta variant, B.1.617.2, now accounts for over 83% of new infections in the United States. And unlike past variants, this one is spreading among both vaccinated and unvaccinated individuals. In fact, CDC documents recently revealed that vaccinated individuals may spread the virus just as easily as unvaccinated people, given similar levels of viral load between the two groups.
There is also a third group of people that we know even less about in the context of the variant’s transmissibility: people who are unvaccinated but potentially have some degree of natural immunity from previous coronavirus infection. Nobody knows exactly how long their immunity will last and what levels of protection they have against the delta variant. But early research has indicated that natural immunity may not supply sufficient protection against the delta variant.
Understandably, this is all worrisome. But it is important to consider the effect of infection on different populations. And that brings us to our next factor.
2.Vaccine effectiveness against serious illness from delta—and uptake among unvaccinated individuals
No vaccine can provide 100% protection—and it's important to remember that most vaccines are designed to prevent serious illness and death, NOT to prevent infection. That is why media reports about fully vaccinated individuals getting infected with the delta variant can be misleading. The important indicator to watch for is not necessarily the infection rate, but how many of those infections lead to serious illness or death. If a breakthrough infection is usually asymptomatic or mildly symptomatic, the main concern is spreading the variant to at-risk populations—namely, unvaccinated people and those with weakened immune systems or underlying medical conditions.
The bad news is, we don't currently have great data on this. The latest CDC data showed that less than 0.004% of fully vaccinated individuals had a breakthrough case that led to hospitalization and less than 0.001% died from a breakthrough case of Covid-19. But CDC Director Rochelle Walensky later clarified that those numbers are based on data from January through June, meaning they do not take into account the worst of the delta variant surge, which picked up in earnest in late June and early July.
But there is some reason to be optimistic: Among the 469 breakthrough cases tracked from the Provincetown outbreak in early July, only four led to hospitalization—and there were zero deaths. And preliminary studies from around the globe suggest that all three vaccines available in the United States still offer protection from the delta variant: two doses of Pfizer-BioNTech is 88% effective at preventing symptomatic Covid-19 and 96% effective against hospitalization, a single dose of Moderna's two-dose vaccine is 72% effective at preventing symptomatic Covid-19, and Johnson & Johnson's single-dose vaccine is 85% effective at preventing severe disease. Even among those vaccinated individuals who do end up in the hospital, we can look at new data from Singapore showing that patients hospitalized due to the delta variant are less likely to require supplemental oxygen and clear the virus faster relative to unvaccinated patients. All of this is reassuring as the data suggests vaccines are largely keeping their promise to stave off serious disease, hospitalizations, and death.
This early research suggests that vaccine uptake will remain one of the most crucial factors in determining how worrisome the current surge is—and how it will impact the health care delivery system. After several months of decline, the national vaccination rate is now at its highest level in over a month, and we are observing the most notable increases in vaccine uptake in states with the highest case rates.
3. Vaccine immunity duration
The delta variant has not only prompted a renewed push to increase vaccinations among the previously unvaccinated, but it has also raised questions about the duration of immunity among those who may have been vaccinated several months ago. While the latest data on vaccine duration is not specific to the delta variant, it does suggest that overall efficacy may begin to decline around the six-month mark.
That information, coupled with the increase in breakthrough infections since the delta variant emerged, has accelerated the debate over whether booster shots are needed. Federal regulators are currently researching whether a booster shot is required, and recently announced plans to accelerate extra vaccine doses to immunocompromised individuals. We expect that this is an area where the research will continue to evolve quickly—researchers are learning more on a week-by-week basis. We’ll be keeping a close eye on what the latest research says and how the federal government responds in developing a plan for potential booster shots.
4. Severe Covid-19 cases among children under 12
Rates of Covid-19 infection and severe illness have been relatively low among children. However, it's worth noting that small numbers of children have been hospitalized from the virus, and it can cause long-term side effects like MIS-C and "long Covid-19." CDC has not yet released data showing delta variant symptoms among children, but some children's hospitals have reported increases in hospitalizations related to the delta variant.
Pfizer and Moderna are in the process of clinical trials testing the safety of their vaccines for children under 12. But it may be months before those trials lead to decisions, and children in some parts of the country have already begun to return to school in person. Without a vaccine, a child's only practical defense against spreading and getting the virus is following public health guidelines like hand washing and mask wearing. But some states—Iowa, Florida, Montana, Arizona, and North Dakota—have passed laws that prevent local governments from mandating masks. Many more states have passed laws making mask mandates harder to implement, like the Kansas law allowing citizens to sue their local government over Covid-19 restrictions.
As school resumes in the United States, we will have to pay close attention to the transmissibility Covid-19 among unvaccinated children, the severity of such cases among children, and the potential long-term effects.
5. Hospitalization rates, particularly at the local level
Plain and simple—the higher the number of hospitalizations, the more worried we should be. Hospitalizations tell us how many people have more severe cases of Covid-19. But they also tell us what level of strain the U.S. health care system is under.
So, what are we seeing right now? CDC's latest 7-day average shows nearly 50,000 people hospitalized across the United States, which is similar to rates seen last summer. Unsurprisingly, there is regional variation, with some states experiencing worse flareups than others. Most of the highly impacted regions have low vaccination rates: On Monday, there were more Covid-19 hospitalizations in Florida than at any other time in the pandemic. In Louisiana, hospitalizations have spiked to "never-before-seen levels," breaking the previous record set in January—and leading to expectations that facilities will be overwhelmed again. As we move forward, we may see "hyperlocal outbreaks," where low-vaccination regions surrounded by high vaccination areas could end up with concentrated outbreaks.
It's important to keep an eye on local vaccination rates because it's clear that unvaccinated individuals and communities are more vulnerable. But that doesn't mean communities with higher vaccination rates are immune. Given the fact that there is more interconnectedness than ever between communities today, and the fact that we haven't achieved true herd immunity even in areas with relatively high vaccination rates, even "highly" vaccinated communities could see outbreaks. For example, intensive care units are filling up with Covid-19 patients in Santa Monica, California, where roughly 80% of residents are vaccinated.
At this point, it seems clear that there will be a heightened strain on hospitals relative to the previous few months of "calm"—and data from abroad suggests it may get worse before it gets better.
6. Covid-19 trends in 'bellwether countries'
Recent decreases of Covid-19 cases in India and the U.K. are a heartening sign that recovery from a delta surge is possible. In India, cases peaked at over 400,000 a day in May. Last week, they experienced roughly 39,000 daily cases with a 48% decrease in the daily death count—a stark reduction. In the U.K., cases have dropped from roughly 47,000 in mid-July to nearly 27,000 the first week of August, even after their government lifted nearly all Covid-19 restrictions.
Sudden spikes may have been fueled by mass congregations of people: the EuroCup in England, April election rallies in India, and fourth of July celebrations in the United States. The subsequent declines in India and the UK suggest that delta could move through a crowd quickly and limiting large crowd gatherings could help stem the spread. It's also possible that herd immunity is behind the rapid decrease, due to the combination of vaccination rates and infection levels. That could be a hopeful sign for regions of the U.S. that are struggling with high infection rates now but seeing increases in vaccinations.
But we’ll want to continue watching the research closely. Scientists aren’t yet sure exactly what lead to the rapid declines, meaning we can’t be entirely confident that the United States. will follow the same trajectory as the U.K. and India.
7. Global vaccination rates—and the emergence of new variants
The United States is just one part of an interconnected world. It impacts (and is impacted by) global trends in health. It’s overwhelmingly clear—everything we do is a collaboration, and moving through this pandemic is no exception.
To date, about 27% of the global population has been vaccinated. The latest vaccination rate is roughly 42.5 million doses per day, which means it will take at least another five months to cover 75% of the world's population. Just a few short months ago, the global vaccination rate had us estimating we’d need more than 4.6 years to achieve global herd immunity with two-dose vaccine regimens.
Five months is better than 4.6 years, but that assumes the vaccination rate will remain the same. With ongoing vaccine hesitancy and inequitable access in low-resource countries, we shouldn’t just assume this will be the case. If we see a drop in global vaccination rates, we will see an extension in the time it takes to reach a semblance of global herd immunity. The more time we spend in this phase, the more opportunities the coronavirus has to mutate into the next variant. And the next variant could be even more transmissible and deadlier than the delta.
Even with President Biden's pledge to donate half a billion Pfizer vaccines to 92 low- and lower middle-income countries by June 2022, stronger efforts are needed to see a faster global impact. And efforts to increase the global vaccination rates could mean trade-offs elsewhere. For example, the World Health Organization has pled for a moratorium on booster shots until September to allow lower-resourced nations ability to receive initial vaccinations.
2 factors that may be distracting your response to the delta surge
Knowing what not to focus on is just as important as knowing what to focus on. And there are two factors in particular that have grabbed a lot of the headlines—but that actually tell us very little without additional context.
1. Covid-19 case counts
Case counts alone are no longer sufficient for tracking the severity of any variant, or the virus as a whole. But with the advent of the vaccine and better understanding of how to treat the virus, the calculus has changed, and so too should the metrics we give our attention to. It’s been clear for some time that the goal is not necessarily to eliminate Covid-19 (in fact, research increasingly suggests it's highly likely to become endemic). Instead, we should aim to protect against severe illness and ensure our system has enough capacity to treat sick patients. Severity of illness—and corresponding hospitalization rates—are far more important metrics to track at this point.
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As detailed above, the latest research continues to suggest that vaccines are highly protective in preventing severe illness, even against the delta variant. So as more people get vaccinated, case count numbers are likely to become less accurate. They run the risk of either overestimating the problem (if most cases are only mildly symptomatic) or underestimating the problem (if we miss a lot of asymptomatic people who can still spread the virus to the more vulnerable).
2. The percentage of total infections and hospitalizations that are breakthrough cases
We’ve all seen the recent headlines highlighting the large numbers and percentage of breakthrough infections. Here’s the thing to remember: This is exactly what we would expect to see as vaccination rates increase. The number of breakthrough infections and hospitalizations will increase as more people get vaccinated. The outbreak in Provincetown highlights this well. Yes, roughly 75% of cases were among vaccinated individuals, but most individuals there were vaccinated. Naturally, a high percentage of the cases would be "breakthrough." And remember, very few were hospitalized and no one died from a breakthrough case as a result of that outbreak.
Breakthrough infections alone are not a bad thing. Breakthrough illness, on the other hand, is more worrisome. If we see the rates of breakthrough illness increase, then it’s time to worry a bit more.
It's easy to feel overwhelmed with the constant updates related to Covid-19. While there are more than seven factors you could follow, I believe these are the most important right now. And the clear thread that runs through all of these is that vaccines remain one of the key solutions to move through this pandemic. It's becoming clearer that Covid-19 is unlikely to go away—new variants will arise and so will respective public health measures. But if there is one thing I can confidently say right now, it is that the more vaccinations that are administered in the United States and around the world, the less worried we can all be.
Advisory Board's Heather Bell and Andrew Mohama contributed to this article. Pam Divack, Katie Schmalkuche, Thomas Seay, Vidal Seegobin, Darby Sullivan, and Paul Trigonoplos contributed additional research.