Delta is the “variant of the future” come early. This is how one of the most regarded COVID immunologists in the United States describes the mutant strain that’s now causing surges in Missouri and other low-vaccination states, filling hospitals with younger sets of patients.
It’s another exhausting twist in an outbreak defined by them. Before delta was detected in India and dubbed B.1.617.2, new versions of the coronavirus had been worrisome but manageable despite their faster spread.
Rapid-fire research had demonstrated our immune systems are sturdy and that a full course of COVID-19 vaccines could shield us against the early mutants. Even partial vaccination or immunity built up after infection with the original strain—SARS-CoV-2 classic—provided protection.
But studies this month from the United Kingdom shift the immunity narrative. According to the latest findings from Public Health England, one dose of COVID-19 vaccine—specifically Pfizer and AstraZeneca—cannot withstand the delta variant.
When it comes to preventing symptomatic cases of the delta variant, the vaccine effectiveness after one dose drops to 35%. Compare that against 79% with two doses. For hospitalization, a single dose offers 80% effectiveness, while two shots give 96%.
What does all of this mean for U.S. areas with relatively solid rates of COVID-19 vaccination, such as New York? The worry isn’t that people are skipping second shots. Nearly nine out of 10 Americans complete their two-dose vaccines courses, according to data from New York City and the Centers for Disease Control and Prevention.
If you're unvaccinated, you will get infected, and you will have a higher probability of ending up in the hospital.
Researchers say the real problem is that one-dose recipients offer a preview of what happens to people who live on the margins of solid immunity. If you got infected and recovered, banking on your natural defenses might no longer ward off the delta variant. A shot is needed.
“If you're unvaccinated, you will get infected, and you will have a higher probability of ending up in the hospital,” said Dr. Theodora Hatziioannou, a virologist at Rockefeller University in New York City. “The vaccinated people might get infected too, but they will deal with this a lot better.”
The unvaccinated—particularly younger adults and grade-school children—now appear to be at higher risk for cases and hospitalization than when the dangerous alpha variant (B.1.1.7) sprouted in the U.K. There, delta rose to become the dominant variant of coronavirus there in nine weeks. It now makes up 95% of British cases, primarily consisting of unvaccinated people under 50 years old.
“We seem to be following the pattern with the delta variant, with a doubling time of about two weeks,” Dr. Anthony Fauci, chief medical adviser to the president, said June 22nd during a White House briefing.
Places with the best vaccination rates are starting to see resurgences, too. New York City data show the delta variant accounts for nearly a quarter of analyzed cases, up from 5% the week prior. Similar jumps have been recorded across the Northeast and out west in California. Israel is witnessing fresh outbreaks because of the delta variant despite 84% of adults being fully inoculated. In New York City, that rate is only 60%.
“Our healthcare leadership believes that the best answer to the variant is just keep deepening the vaccination effort,” Mayor Bill de Blasio told the Brian Lehrer Show on Friday. “But Brian, we're going to watch it carefully. There's no evidence at this moment that it changes the trajectory. But if anything occurs, when we have to make adjustments, we will make them quickly.”
But while the vaccines are still expected to prevent serious illness caused by the delta variant in healthy immune systems, more harm will likely come in senior citizens or people with weakened immunity due to pre-existing conditions. In the U.K., deaths are rising among older adults who are fully vaccinated. Israeli officials are reinstating some mask mandates for those who’ve taken shots, a policy recommendation echoed by the World Health Organization.
To gauge what might happen going forward, let’s break down how the delta variant could affect New Yorkers based on their vaccine status. The COVID-19 vaccine rollout has undoubtedly dropped cases and hospitalizations to all-time lows. But due to sizable gaps in coverage, the question is whether the Empire State can sustain its progress everywhere now that life has reopened.
The Unvaccinated
Early estimates suggest that delta can outpace its highly transmissible cousin—the alpha variant—and that it spreads about twice as fast as the original strain of the coronavirus.
To comprehend just how fast that is, let’s hit reset on the COVID outbreak in the Bronx.
Say this borough of 1.4 million people had never experienced the pandemic. There was no vaccine campaign, and no one was wearing masks or social distancing. The whole population and their immune systems were unacquainted with SARS-CoV-2 or its variants. Until one day, 10 people with the disease show up.
The delta variant would hit the Bronx harder and faster than its predecessors—as judged by the standard model for recreating outbreaks. The delta outbreak would peak after about two months, with more than 67,000 cases in a single day. By comparison, an alpha epidemic would take three months to hit full steam, amassing about 47,000 infections during its worst day. The classic strain is way behind, summiting with 26,000 cases at around four and half months.
“It's really important to build these types of models because it's often difficult to grasp how something like this is going to play out in reality,” said Patrick Wedlock, a senior research analyst with the Public Health Informatics, Computational and Operations Research (PHICOR) team at The City University of New York.
This simple model doesn’t precisely tell us how the delta variant will spread through the Bronx this summer, given 41% of the borough has been fully inoculated as of June 27th. Although that’s the lowest vaccination rate in the city, it’s been enough to blunt the Bronx’s pandemic this year. But even the delta variant could thrive in this environment:
“Those who are unvaccinated have the greatest risk of becoming seriously ill, which is why the New York State Department of Health urges all eligible New Yorkers to get vaccinated as soon as they are able,” a state health department spokesperson said in a statement to WNYC/Gothamist.
Recovered But Unvaccinated
Part of this transmission equation also centers around the strength of human immunity and how long it lasts. Thanks to a staggering amount of research, scientists have a sense of how these defenses work during the first 6-12 months after an infection or vaccination.
“What we have learned in a short timespan is amazing,” Dr. Nathaniel Landau, a virologist at New York University’s Grossman School of Medicine who studies mammalian immune systems. “It's been incredible to see how the biomedical research community has come together to answer questions and to learn about the virus and to develop vaccines.”
Recent experiments from his lab and others show that the variants spread faster in part because their mutations allow the virus to stick more firmly to ACE2, the protein doorway coating our cells. These genetic changes also make it harder for our immune systems to spot and defend against the variants.
Antibodies and T cells tend to dominate this conversation around our immune defenses. Both turn on within days of infection or vaccination, but each shield comes with its own capabilities. Antibodies scan the surface of germs but can only recognize familiar features, such as parts of coronavirus’s spike protein. T cells are immediately more versatile.
“T cells have the ability to see more than just the spike protein, so they can see all the internal parts of the virus,” Landau said. “Whereas the antibodies can only see the thing that's sticking out of the virus.”
The limited scope of antibodies becomes key when distinguishing between run-of-the-mill immunity after infection versus the extra oomph offered by vaccination. Merely catching the coronavirus produces a less consistent antibody response, when researchers look from patient to patient. T cells, so far, show sturdier protection against the virus and its variants, both after infection or vaccination.
“What we know is that following infection, the neutralizing antibody titers vary greatly between individuals,” said Hatziioannou from Rockefeller University. “Some have quite strong responses, but others have really, really low responses.”
In a study published June 14, Hatziioannou and her colleagues show the antibodies aren’t static early on but are consistently refining themselves to thwart the coronavirus better. Their team and others found that just one dose of vaccine can enhance this process, widening the antibodies’ scope. Their results help explain why health officials recommend shots even for people who’ve been previously infected with the coronavirus.
“You just have greater quality antibodies being produced at greater levels. You have neutralizing antibody titers that are really exceptionally high,” Hatziioannou said. “And they are able to neutralize not only the parental viruses that circulated but also all the variants that we looked at. They're really remarkable.”
Why does this matter? Antibodies are the major players in whether you’ll get reinfected. They halt the virus as soon as it comes into contact with our organs. T cells are powerful, but they’re more involved with clearing the virus after it’s already arrived and preventing symptoms.
“There have been a few rare cases of reinfection, but the large majority of people are protected by the antibodies from becoming reinfected,” Landau said. “We see antibodies in a vaccinated person are about five times stronger than the antibodies that you get from the natural infection.”
Fully Vaccinated
Reinfections appear to be mercifully rare among the fully vaccinated, with only 13 cases detected out of 10,000 screened in the latest iteration of Britain’s SIREN study. Landau said he wouldn’t be surprised if reinfections are more prevalent among inoculated people but are simply asymptomatic and overlooked. But that could ultimately be a healthy thing.
“The immune system needs to be in good shape, just like an athlete. It needs to stay in practice. When you do have such a low-level infection, it strengthens your immune response and will protect you for longer,” Landau said. “What's happening in real life all the time is that we are getting infected by viruses in an asymptomatic way. So you don't know that you're getting infected, but your T-cell response, as a result, gets strengthened.”
COVID-19 has taught us the value of stopping disease before it gains momentum. This lesson applies on a national level as well as to our immune systems. The difference between a severe or mild case can depend upon whether a person’s defenses respond slowly or softly.
The COVID-19 vaccines reinforce the body, ensuring that everyone starts on a stronger footing if the virus shows up. With the shots, weaker immune systems become stout, and the sturdy becomes ironclad. This armory can definitely last for months—but potentially for years.
But the variants are tearing at the margins. Public Health England has recorded about 92,000 delta cases as of June 25th. These infections and their overnight hospitalizations are twice as common in unvaccinated people, most of whom are younger than 50. Schools appear to be the primary drivers of these new outbreaks, bucking the longstanding trend with the coronavirus.
“The Imperial College of London did a study in over 100,000 homes and found that youth were driving the U.K. surge,” Fauci said during the briefing, “with a fivefold higher positivity among children (5 to 12) and young adults (18 to 24) versus people older than 65.”
And among those with COVID-19 shots, deaths are occurring more often in adults over 50, an age bracket where immune systems are more likely to be weaker before vaccination.
The clear message is to get vaccinated with a full course of COVID-19 vaccine as soon as you can. Two doses of Moderna are expected to offer solid protection against the delta variant, given it is an mRNA vaccine like Pfizer.
The jury is still out on the Johnson & Johnson vaccine, despite comments from a former FDA commissioner who claimed it is only 60% effective against the delta variant, based on findings with the AstraZeneca shot.
While Johnson & Johnson and AstraZeneca use similar biotechnology platforms, “the antigen is presented slightly differently by the two vaccines,” said Hatziioannou from Rockefeller University. “The antibody response from the Johnson and Johnson would be more similar to the mRNA vaccines than the one from AstraZeneca.”
Dr. Céline Gounder, an infectious disease specialist and epidemiologist at the NYU Grossman School of Medicine and Bellevue Hospital, agrees that more data are needed for the average person who has taken Johnson & Johnson’s single shot. But the calculus will likely be different for someone at very high risk for severe disease, senior citizens, immunosuppressed individuals and people with underlying medical conditions.
“If you are at increased risk for not responding to the vaccine or have an increased risk of severe disease,” Gounder said at the WNYC 2021 Health Convening, “in those people, I would recommend getting an mRNA vaccine, a second dose after your Johnson and Johnson. But that second dose should be either Moderna or Pfizer.”
