Vaccination and the Delta Variant: Four Steps Forward, Two Steps Back

Larry Corey, MD

The news is all about Delta, Delta, Delta, for good reason.

The variants are forcing us to ask and answer, again, a whole set of uncomfortable questions.

Sobering findings of the past few weeks have shaken both the American and scientific psyche. People have had to re-assess their perceptions about the COVID-19 vaccines, and the re-emergence of an epidemic many thought was over. Many of us have had to come to terms with how life can sometimes just be complicated.

It’s been a scientific and emotional roller coaster. In the spring, we saw the Alpha variant, which was two times more infectious than the ancestral strain. That was followed by Beta, which was eight times more resistant to laboratory assays and to neutralization with therapeutic antibodies in the petri dish. That variant was worrisome, because it was more capable at resisting vaccines. We were lucky because it was outcompeted by Alpha – a variant that the vaccines could handle.

Now Delta is here and just ripping through both of them, like a hot knife through butter. It’s replacing Beta with the same rapidity that it replaced Alpha and all the in-between variants. It’s now the dominant variant in the US, showing up in more than 90 percent of positive cases.

So, what is it about this Delta, or what I should say, many Deltas?

What we’re seeing is this scientifically fascinating, but epidemiologically disconcerting change in the virus that’s happened at an incredibly rapid pace. Delta has some new characteristics which make it a formidable foe. It’s much more infectious to others; initial viral loads in the nose seem to be somewhat higher than previous strains with more rapid spread into the lungs and other organs within the body.

It is clear that the amount of virus required to infect others is lower, making transmissibility to household and casual contacts more efficient than the other variants. The average person who contracts a Delta infection transmits the virus to between 5 and 9 other people – making this variant far more infectious than the original ancestral strain from a year ago.

Case numbers, predictably, are quickly increasing. Younger adults are being hospitalized. ICUs are filling up. Most disconcertingly, we are seeing more children being admitted in our pediatric hospitals. When we look at who’s in the hospital among adults, we see about 95 to 98% are unvaccinated. The same pattern is seen with children. COVID-19 Delta strain is a hospital epidemic of the unvaccinated.

Yes, we are now seeing outbreaks of Delta in which vaccinated people are infected, such as the one from early July in Provincetown, Massachusetts. These outbreaks involve two behaviors we’ve seen that result in super-spreader events—crowding and indoor revelry with drinking and eating and no masks. Eating, drinking, shouting, singing—spraying forth, shall we say, produce a density of unseen viral particles in the air that people inhale over and over again.

These behaviors are the food of the virus—a heavy smorgasbord of food: all advantageous to the virus. The result is that we are seeing humans get infected. For the vaccinated, this means just mild infection. But for the unvaccinated, we are seeing rapid spread of the virus to the lungs and other parts of the body.

With more than 100,000 cases a day being tallied nationwide, it’s clear we need to take some new countermeasures to slow the spread.

We’ve seen a necessary reintroduction of masking. Just when many people were ready to celebrate, or breathe a sigh of relief, many of us are now back in an anxious position. Questions that we might have thought were settled a month ago are suddenly back in play.

Will our children be able to safely go back to school? Can we safely go back to work? Will we ever be able to relax and enjoy dinner indoors again with friends, extended family, or in professional settings?

Delta is disconcerting to all of us.

Last week, I cancelled a CoVPN (COVID-19 Prevention Network) scientific meeting in October—one that I’d been eagerly planning and anticipating for months. We wanted to meet and celebrate/review the work the network has done in developing effective COVID-19 vaccines at unprecedented, record-setting pace.

The success of the program and the hard work and toil have shaped the careers of many scientists on this team. In some ways, it has shaped entire worldviews. We wanted to revel in the camaraderie of the team’s success and do so in person. But it was clear—even though the event required vaccination to attend, no one wanted to come to Seattle to celebrate with the possible risk it would carry if anyone contracted Delta and had to be quarantined away from home.

Let’s look at vaccination and Delta as it relates to the US:

  • The mRNA and Janssen vaccines both are highly effective against death and hospitalization (greater than 90 to 98%).
  • The protection from getting symptomatic COVID-19 appears to be a bit less with the Delta variant—studies show a range from 85% to 40%–and this may differ by time post vaccination. But in all studies the severity of illness is markedly less—the immune system of vaccinated persons can rapidly clear Delta. As noted above, severe disease among the vaccinated in the US with the mRNA or Janssen vaccines is rare.
  • Transmission to others from vaccinated persons can occur, but it is less than from the unvaccinated population, although we have not yet demonstrated how much less.

So, yes, one can still get infected with Delta despite being vaccinated if one doesn’t use precautions. That’s a fact. But a bigger fact is that you won’t get very sick, and you can reduce the risk of acquiring COVID-19 and spreading it if you wear a mask.

Perhaps we shouldn’t have been surprised. We understood that reducing acquisition of COVID-19 was a harder goal than ameliorating disease. But we do know the vaccines work and countless lives have been saved by them. So, the vaccines have markedly changed the dynamic of our thought process, but maybe what we need is to change our expectations.

What do I mean by that?

Well, the virus is teaching us another important lesson—its amazing speed to adapt. It’s hard to understand how a virus like this is rolling through the world. But rolling through, it is. Recent data out of Israel estimates that every six to nine days the Delta infection among its population doubles. As Israel has the highest percent vaccination rate (with Pfizer/BioNTech mRNA) of any adult population in the world, this is at first glance surprising. However, not when one recognizes that younger people are not yet vaccinated, and it’s the unvaccinated who are the main fuel for that kind of rapid spread.

Why is it so transmissible? What selective pressure is it under? Delta doesn’t have the obvious neutralization-resistant mutations. What part of the human immune response that you get from vaccination is being delayed by the Delta variant? Will boosters actually slow it down or is it really more important to focus our efforts on reaching the unvaccinated?

These are all scientific questions needing answers. As Israel has made the decision to boost its elderly population, some data about the role that boosting can play in reducing spread will be obtained.

But the boosting issue is a bit of a diversion from the main issue in our country, which is, how do we reduce the spread of this highly infectious variant? 

Do we need a national mandate for vaccination? Is it a personal choice to vaccinate or not? Or do we all have a societal obligation to not be the fuel to this ongoing forest fire? The unvaccinated in some respects are an unsuspecting accomplice to the arsonist at large—they serve as bone-dry tinder for the lighted match.

Should we rethink this?

Our body politic is focused on extreme individualism, and isn’t allowing a universal approach to public health. In such an environment where political leadership is limited, do our corporate leaders who can mandate vaccination step up to the plate?

There are some who are pointing to government action, namely through a full approval of the vaccines by the FDA. But does anyone really believe that the Emergency Use Authorization is that much different than the FDA licensing it under a full Biologics License Application? Yes, there are important steps to licensing the medication so that there is consistency from lot to lot in manufacturing. But at 400 million vaccinated and growing daily, we have ample safety and efficacy data.

So, yes, official product licensure is, to this author, not an appropriate reason to hold back mandated vaccination. We already know the vaccines are extraordinarily effective, and powerful tools for fighting back against the pandemic. Each day the documentation of the positive effect of the vaccines grows, and we understand that the virus is continuing to mutate. Cutting off the fuel to the fire is really the only way to slow down the rate of mutational alterations.

It is true that the Delta variant has swept in like a cold, damp morning shrouded by fog. And it’s left us with a bit of a shiver. But like all days, morning turns to afternoon and the sun gets higher in the horizon and some of the fog lifts. Although Delta has taken us two steps back, a much more important step forward is to continue to vaccinate as many of our citizens as we can – here in the US and around the world.

Once we do, Delta may move itself two steps back, putting us once again two steps forward toward pre-COVID-19 normalcy.

Dr. Larry Corey is the leader of the COVID-19 Prevention Network (CoVPN) Operations Center, which was formed by the National Institute of Allergy and Infectious Diseases at the U.S. National Institutes of Health to respond to the global pandemic and the Chair of the ACTIV COVID-19 Vaccine Clinical Trials Working Group. He is a Professor of Medicine and Virology at University of Washington and a Professor in the Vaccine and Infectious Disease Division and past President and Director of Fred Hutchinson Cancer Research Center.

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