Since the early days of the pandemic, we’ve known that COVID-19 is caused by a novel coronavirus named SARS-CoV-2, a strain of virus that had never before been identified in humans. Part of the challenge of this global outbreak has been how scientists have had to race to understand a virus the world had never quite seen before.
Scientists are still racing to figure out how the virus continues to evolve. Among the top concerns for the global recovery effort right now is the Delta variant, a strain of the virus. Factors such as transmissibility have made Delta a driving force in the latest wave of COVID-19 outbreaks, leading to more concern about where vaccination rates stand as the Northern Hemisphere’s summer season drifts away.
What is the Delta variant? How has the virus changed? And what does it mean for life in the pandemic as we move forward from vaccine rollout to mask mandates to new lockdowns? Here’s what we know.
What is the Delta variant?
Named after a letter of the Greek alphabet, like other variant strains, the Delta variant is a mutated version of SARS-CoV-2 that is considered especially contagious. The Delta variant was first discovered in India, where scientists worried its increased transmissibility was connected to the recent, major wave of infections.
As CNBC reported, White House chief medical advisor Dr. Anthony Fauci said in late June that the Delta variant accounted for 20% of newly diagnosed infections in the United States. During a TODAY show interview, Fauci said he expected the variant would rapidly become the dominant strain in the U.S. based on how it had “exploded” in the United Kingdom. A little under a month later, as the New York Times reported, the director of the CDC said, on July 20, that the agency estimated that 83% of new cases in the U.S. were caused by Delta.
Research indicates that what makes Delta especially dangerous is its heightened transmissibility. In an interview with STAT News, Céline Gounder, an NYU infectious disease professor and member of the Biden-Harris Transition Covid-19 Advisory Board, said that Delta is “about a thousand times more infectious than the original strains of the virus.”
Research conducted in China indicated that people infected with Delta had approximately 1,000 times the viral load at the time of their first positive test when compared with people who had the original strain of the virus. According to Yale Medicine, one Scottish study found that Delta doubled the likelihood of hospitalization in unvaccinated individuals; but some data has shown no significant difference in severity between Delta and the Alpha strain from the U.K. Research published in February found that peak viral load levels were congruent with being highly contagious in infected people.
“With the Delta variant, we’re seeing very fleeting contact leading to transmission,” Dr. Jeannette Young, chief health officer for Queensland, Australia, said at a recent press conference, according to the Guardian. “At the start of this pandemic, I spoke about 15 minutes of close contact being a concern. Now it looks like it’s five to 10 seconds that’s a concern. The risk is so much higher now than it was only a year ago.” In Australia, where Delta has surged, closed circuit television footage captured a transmission that involved two people simply walking past each other.
As the Associated Press reported, World Health Organization (WHO) director-general Tedros Adhanom Ghebreyesus said at a June 25 press conference that the Delta variant is “the most transmissible of the variants identified so far.” Ghebreyesus stressed that viral evolution is inevitable, but limiting transmission limits the prevalence of variants.
Ghebreyesus also said that a global community failure to effectively allocate vaccines has created worrisome situations for low-income countries. “It’s becoming so dangerous, and the difference now is between having a vaccine and not having a vaccine; the differences between the have and have-nots, which is now completely exposing the unfairness of our world, the injustice, the inequality,” Ghebreyesus continued. He pointed out that global vaccine supply lines play a role in how variants evolve and emerge.
Despite that, experts are hopeful that hospitalizations and deaths won’t rise with the new cases. “We’re seeing the cases shoot up more steeply than we are seeing hospitalizations and deaths shoot up,” Gounder told STAT News in that July 23 interview. “That said, it remains to be seen whether that decoupling holds because we’re still early in our own surge with Delta.”
Do vaccines work on the Delta variant?
Of concern to many are the possibilities for breakthrough cases as well as breakthrough disease, in which a vaccinated person could develop significant symptoms. But in studies, several major vaccines are proving effective at protecting against severe disease caused by the Delta variant.
According to a blog post from Yale Medicine, an analysis by Public Health England found Pfizer-BioNTech’s vaccine was “88% effective against symptomatic disease and 96% effective against hospitalization from Delta.” Meanwhile, Oxford-AstraZeneca’s formula, which is not an mRNA vaccine like Pfizer’s, was found to be “60% effective against symptomatic disease and 93% effective against hospitalization.”
A late-June press release from Moderna said the company has “encouraging” clinical data about its mRNA vaccine’s efficacy with new variants. Data on Johnson and Johnson’s single-dose vaccine has been mixed. Some have sought follow-up shots of mRNA vaccines, as CNBC reported.
Experts told CNN in June that some U.S. states with low vaccination rates could be at higher risk for Delta variant outbreaks. Meanwhile, the Associated Press reported last month that many states have vaccine surpluses and officials worry some of the medicine could hit its expiration date before it gets used.
According to the CDC’s COVID Data Tracker, 56.8% of the total U.S. population has received at least one dose and 49.1% is fully vaccinated. Those numbers jump to 66.5% for one dose and 57.5% for fully vaxxed when you exclude people under 12, for whom there is currently no authorized vaccine to use. At the urging of the Food and Drug Administration (FDA), vaccine trials are underway for people ages five to 11, the New York Times and Washington Post reported this week. One FDA official told NBC News earlier this month that vaccines for people under 12 could be ready sometime this winter.
Should we still be wearing masks?
Mask mandates have already been re-employed in some areas where infections are surging. The CDC issued new guidance on July 27 for areas with high transmission, with director Dr. Rochelle Walensky saying, “The CDC recommends fully vaccinated people wear masks in public, indoor settings to help prevent the spread of the Delta variant and protect others.”
“This includes schools,” Walensky explained. “CDC recommends that everyone in K to 12 schools wear a mask indoors, including teachers, staff, students, and visitors, regardless of vaccination status. Children should return to full-time, in-person learning in the fall with proper prevention strategies in place.”
“With the Delta variant, vaccinating more Americans now is more urgent than ever," Walensky added. “The highest threat of cases and severe outcomes is happening in places with low vaccination rates and among unvaccinated people. This moment — and most importantly, the associated illness, suffering, and death — could have been avoided with higher vaccination coverage in this country.”
The WHO had already said that, yes, even vaccinated people should mask up. “What I can say is that when we take measures to prevent transmission, we take measures to prevent transmission against droplet and aerosol and airborne,” Dr. Maria Van Kerkhove, WHO’s COVID-19 technical lead, said at the June 25 press conference. “Take those measures. Wearing that mask. Making sure you have clean hands when you put on and you take off a mask. Make sure that if you are indoors, that you have good ventilation. In some situations it is as simple as opening up a window, if it’s safe to do so.”
“We need to ensure that people who are sick and infected don’t get the opportunity to infect others. We have to ensure that the environments we work in, be it the air or the surfaces in the environments we’re in, are appropriately sanitized,” said Dr. Mike Ryan, executive director of WHO’s Health Emergencies Programme. “We have to reduce our own exposure, so we get exposed to less virus, which is the infectious dose, and we have to ensure we’re wearing masks and doing other things to prevent us inhaling particles that will cause us to be sick.”
“What we’re saying is: Once you’ve been fully vaccinated, continue to play it safe because you could end up as part of a transmission chain,” Dr. Bruce Aylward, a senior advisor to the WHO director-general, said at the same press conference last Friday. “I think the first message we want to be careful about is saying, ‘Once you’re vaccinated you can just go ahead and do whatever.’ Yes, you can reduce some measures, and different countries have different recommendations in that regard, but there is still the need for caution.”
How are COVID-19 measures changing in some places?
As the Delta variant spreads, governments around the world have been reinstating some levels of COVID-19 restrictions, from indoor mask mandates to full lockdowns.
According to the BBC, at the end of June, the Israeli government reimposed an indoor mask mandate that had been lifted 10 days earlier. That move came after a spike in new cases, the majority of which were linked to the Delta variant, and some of which occurred in fully vaccinated people. But Prime Minister Naftali Bennet said at the time that new hospitalizations weren’t rising complementarily. Israeli doctors recently told Haaretz that, while hospitalizations have risen, patients are experiencing milder illnesses. At 59% as of July 27, Israel has one of the highest full- vaccination rates in the world, according to data compiled by Our World in Data and the New York Times.
In Australia in late June, four major cities were dealing with new lockdowns potentially affecting millions of people, CNN reported. According to the BBC, the moves came as the Delta variant made it through Australian defenses, prompting the largest lockdown there since the one that began the pandemic. Reuters now reports that one Australian state is set to lift those restrictions, but New South Wales, the state that includes the city of Sydney, will not. According to the Guardian, New South Wales is experiencing an all-time high for daily cases after a month of lockdown. Data indicates that 13% of the country’s population is fully vaccinated, as of July 27.
Indonesia, the world’s fourth most-populous nation, where less than 7% of the population is fully vaccinated, locked down two major islands earlier in July, including the island on which the capital, Jakarta, is located, CNN reported. According to Reuters, that lockdown has been extended, but the nation’s president also says infections and hospitalizations in some areas have started to decline.
In Bangladesh, a strict lockdown was put in place in late June and extended in early July, with restrictions paused for eight days for celebrations of Eid al-Adha, as the Associated Press reported. Officials said that Monday, July 26, set records in the country for new cases and deaths, according to Al Jazeera. Less than 3% of the population is fully vaccinated.
Editor's note: This story was originally published on June 29. It was updated with new information on July 27.
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