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Vaccine Blogs

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

The views and opinions expressed here are those of the authors and do not necessarily reflect the position of either Johns Hopkins University and Medicine or the University of Washington.

Larry Corey, Professor of Medicine
August 16, 2021
  • The Delta variant is more transmissible than prior variants and case numbers are quickly increasing.
  • Among hospitalized adults, nearly all are unvaccinated, which speaks to the power of the Covid-19 vaccines.
  • Delta has underscored the importance of vaccinating as much of the population as possible.

The recent media headlines are all Delta, Delta, Delta, and it’s not the airline. The last several weeks have brought sobering findings that have produced a large alteration in both the American and scientific psyche about COVID-19 vaccines, the trajectory of the epidemic, and the understanding that life can sometimes just be complicated. We first saw the Alpha variant, which was two times more infectious than the ancestral strain, followed by Beta, which was eight times more resistant in laboratory assays to neutralization, and which also reduced vaccine efficacy. And now Delta is here and just ripping through both of them, like a hot knife through butter, replacing Beta with the same rapidity that it replaced Alpha and all the in-between variants.

So, what is it about this Delta, or what I should say, many Deltas? Because what we’re seeing is this fascinating, scientific change in the virus that’s happened at incredible rapidity. Delta has some new characteristics that make it a formidable foe. It’s much more infectious to others; initial titers of the virus in the nose seem to be 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. Case numbers are quickly increasing, ICUs are filling up, and 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 an unprecedented number of people who have not been vaccinated – 95 to 98 percent. 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. These outbreaks involve two behaviors 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, produces a density of unseen viral particles in the air. 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.

We’ve seen a necessary reintroduction of masking in our country and a return of anxiety to much of the populace. 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. Today, I cancelled a COVID-19 Prevention Network (CoVPN) scientific meeting scheduled for 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. The success of the program and the hard work and toil have shaped professional careers dramatically, if not 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 U.S.:

  1. The mRNA and Janssen vaccines are highly effective against death and hospitalization (greater than 90 to 98%).
  2. 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 U.S. with the mRNA or Janssen vaccines is rare.
  3. 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: it can adapt with amazing speed. 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 the Pfizer/BioNTech mRNA vaccine) of any adult population in the world, this is at first glance surprising. However, it’s less surprising when one recognizes that younger people are not yet vaccinated, and it’s the unvaccinated that are the main fuel for that kind of speed.

Why is it so transmissible? What selective pressure is it under? It 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 disease 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 personal choice to vaccinate or not the defining moment here? Or is the defining moment that we all have a societal obligation to not be the fuel for the 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 politics are not allowing a universal approach to public health. Do our corporate leaders who can mandate vaccination step up to the plate? Does anyone really believe that the Emergency Use Authorization is that much different than the FDA licensing it under a full Biologics License Application? Does any argument saying that the FDA hasn’t certified it bring out any sense of credulity? 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. Each day the documentation of the positive effect of the vaccines grows, and we understand that the virus is continuing to mutate. So, decreasing the fuel options 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. Once we do, Delta may move itself two steps back, putting us once again two steps forward toward pre-COVID-19 normalcy.

Larry Corey, Professor of Medicine

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 US 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.