A highly contagious form of the coronavirus known as the Delta variant is spreading rapidly and becoming increasingly prevalent around the world. First identified in India in December, Delta has now been identified in 111 countries.
In the United States, the variant now accounts for 83% of sequenced COVID-19 cases, said Rochelle Walensky, director of the Centers for Disease Control and Prevention, at a July 20 Senate hearing. In May, Delta was responsible for just 3% of U.S. cases. The World Health Organization projects that Delta will become the dominant variant globally over the coming months.
So, how worried should you be about the Delta variant? We asked experts some common questions about Delta.
What is a variant?
To understand Delta, it's helpful to first understand what a variant is. When a virus infects a person, it gets into your cells and makes a copy of its genome so it can replicate and spread throughout your body.
In the process of making new copies of itself, the virus can make a mistake in its genetic code. Because viruses are replicating all the time, these mistakes — also called mutations — happen pretty often. A new variant emerges when a virus acquires one or more new mutations and starts spreading within a population.
There are thousands of SARS-CoV-2 variants, but most of them don't substantially change the way the virus behaves. The variants that scientists are most interested in are known as variants of concern. These are versions of the virus with mutations that allow the virus to spread more easily, evade vaccines, or cause more severe disease.
"The vast majority of the mutations that have accumulated in SARS-CoV-2 don't change the biology as far as we're concerned," said Jennifer Surtees, a biochemist at the University of Buffalo who's studying the coronavirus. "But there have been a handful of key mutations and combinations of mutations that have led to what we're now calling variants of concern."
One of those variants of concern is Delta, which is now driving many new COVID-19 infections.
Why is the Delta variant so concerning?
"The reason why the Delta variant is concerning is because it's causing an increase in transmission," said Alba Grifoni, an infectious disease researcher at the La Jolla Institute for Immunology. "The virus is spreading faster and people — particularly those who are not vaccinated yet — are more prone to exposure."
The Delta variant has a few key mutations that make it better at attaching to our cells and evading the neutralizing antibodies in our immune system. These mutations have changed the virus enough to make it more than twice as contagious as the original SARS-CoV-2 virus that emerged in Wuhan and about 50% more contagious than the Alpha variant, previously known as B.1.1.7, or the U.K. variant.
These mutations were previously seen in other variants on their own, but it's their combination that makes Delta so much more infectious.
Do vaccines work against the Delta variant?
The good news is, the COVID-19 vaccines made by AstraZeneca, Johnson & Johnson, Moderna, and Pfizer still work against the Delta variant. They remain more than 90% effective at preventing hospitalizations and death due to Delta. While they're slightly less protective against disease symptoms, they're still very effective at preventing severe illness caused by the Delta variant.
"They're not as good as they were against the prior strains, but they're holding up pretty well," said Eric Topol, a physician and director of the Scripps Translational Research Institute, during a July 19 briefing for journalists.
Because Delta is better at evading our immune systems, it's likely causing more breakthrough infections — COVID-19 cases in people who are vaccinated. However, breakthrough infections were expected before the Delta variant became widespread. No vaccine is 100% effective, so breakthrough infections can happen with other vaccines as well. Experts say the COVID-19 vaccines are still working as expected, even if breakthrough infections occur. The majority of these infections are asymptomatic or cause only mild symptoms.
Should vaccinated people worry about the Delta variant?
Vaccines train our immune systems to protect us against infection. They do this by spurring the production of antibodies, which stick around in our bodies to help fight off a particular pathogen in case we ever come into contact with it.
But even if the new Delta variant slips past our neutralizing antibodies, there's another component of our immune system that can help overtake the virus: T cells. Studies are showing that the COVID-19 vaccines also galvanize T cells, which help limit disease severity in people who have been vaccinated.
"While antibodies block the virus and prevent the virus from infecting cells, T cells are able to attack cells that have already been infected," Grifoni said. In other words, T cells can prevent the infection from spreading to more places in the body. A study published July 1 by Grifoni and her colleagues found that T cells were still able to recognize mutated forms of the virus — further evidence that our current vaccines are effective against Delta.
Can fully vaccinated people spread the Delta variant?
Previously, scientists believed it was unlikely for fully vaccinated individuals with asymptomatic infections to spread Covid-19. But the Delta variant causes the virus to make so many more copies of itself inside the body, and high viral loads have been found in the respiratory tracts of people who are fully vaccinated. This suggests that vaccinated people may be able to spread the Delta variant to some degree.
If you have COVID-19 symptoms, even if you're fully vaccinated, you should get tested and isolate from friends and family because you could spread the virus.
What risk does Delta pose to unvaccinated people?
The Delta variant is behind a surge in cases in communities with low vaccination rates, and unvaccinated Americans currently account for 97% of hospitalizations due to COVID-19, according to Walensky. The best thing you can do right now to prevent yourself from getting sick is to get vaccinated.
Gigi Gronvall, an immunologist and senior scholar at the Johns Hopkins Center for Health Security, said in this week's "Making Sense of Science" podcast that it's especially important to get all required doses of the vaccine in order to have the best protection against the Delta variant. "Even if it's been more than the allotted time that you were told to come back and get the second, there's no time like the present," she said.
With more than 3.6 billion COVID-19 doses administered globally, the vaccines have been shown to be incredibly safe. Serious adverse effects are rare, although scientists continue to monitor for them.
Being vaccinated also helps prevent the emergence of new and potentially more dangerous variants. Viruses need to infect people in order to replicate, and variants emerge because the virus continues to infect more people. More infections create more opportunities for the virus to acquire new mutations.
Surtees and others worry about a scenario in which a new variant emerges that's even more transmissible or resistant to vaccines. "This is our window of opportunity to try to get as many people vaccinated as possible and get people protected so that so that the virus doesn't evolve to be even better at infecting people," she said.
Does Delta cause more severe disease?
While hospitalizations and deaths from COVID-19 are increasing again, it's not yet clear whether Delta causes more severe illness than previous strains.
How can we protect unvaccinated children from the Delta variant?
With children 12 and under not yet eligible for the COVID-19 vaccine, kids are especially vulnerable to the Delta variant. One way to protect unvaccinated children is for parents and other close family members to get vaccinated.
It's also a good idea to keep masks handy when going out in public places. Due to risk Delta poses, the American Academy of Pediatrics issued new guidelines July 19 recommending that all staff and students over age 2 wear face masks in school this fall, even if they have been vaccinated.
Parents should also avoid taking their unvaccinated children to crowded, indoor locations and make sure their kids are practicing good hand-washing hygiene. For children younger than 2, limit visits with friends and family members who are unvaccinated or whose vaccination status is unknown and keep up social distancing practices while in public.
While there's no evidence yet that Delta increases disease severity in children, parents should be mindful that in some rare cases, kids can get a severe form of the disease.
"We're seeing more children getting sick and we're seeing some of them get very sick," Surtees said. "Those children can then pass on the virus to other individuals, including people who are immunocompromised or unvaccinated."
What's the case-fatality rate?
Currently, the official rate is 3.4%. But this is likely way too high. China was hit particularly hard, and their healthcare system was overwhelmed. The best data we have is from South Korea. The Koreans tested 210,000 people and detected the virus in 7,478 patients. So far, the death toll is 53, which is a case-fatality rate of 0.7%. This is seven times worse than the seasonal flu (which has a case-fatality rate of 0.1%).
What's the best way to clean your hands? Soap and water? Hand sanitizer?
Soap and water is always best. Be sure to wash your hands thoroughly. (The CDC recommends 20 seconds.) If soap and water are not available, the CDC says to use hand sanitizer that is at least 60% alcohol. The problem with hand sanitizer, however, is that people neither use enough nor spread it over their hands properly. Also, the sanitizer should be covering your hands for 10-15 seconds, not evaporating before that.
How often should I wash my hands?
You should wash your hands after being in a public place, before you eat, and before you touch your face. It's a good idea to wash your hands after handling money and your cell phone, too.
How long can coronavirus live on surfaces?
It depends on the surface. According to the New York Times, "[C]old and flu viruses survive longer on inanimate surfaces that are nonporous, like metal, plastic and wood, and less on porous surfaces, like clothing, paper and tissue." According to the Journal of Hospital Infection, human coronaviruses "can persist on inanimate surfaces like metal, glass or plastic for up to 9 days, but can be efficiently inactivated by surface disinfection procedures with 62–71% ethanol, 0.5% hydrogen peroxide or 0.1% sodium hypochlorite within 1 minute." (Note: Sodium hypochlorite is bleach.)
Can Lysol wipes kill it?
Maybe not. It depends on the active ingredient. Many Lysol products use benzalkonium chloride, which the aforementioned Journal of Hospital Infection paper said was "less effective." The EPA has released a list of disinfectants recommended for use against coronavirus.
Should you wear a mask in public?
The CDC does not recommend that healthy people wear a mask in public. The benefit is likely small. However, if you are sick, then you should wear a mask to help catch respiratory droplets as you exhale.
Will pets give it to you?
That can't be ruled out. There is a documented case of human-to-canine transmission. However, an article in LiveScience explains that canine-to-human is unlikely.
Are there any "normal" things we are doing that make things worse?
Yes! Not washing your hands!!
What does it mean that previously cleared people are getting sick again? Is it the virus within or have they caught it via contamination?
It's not entirely clear. It could be that the virus was never cleared to begin with. Or it could be that the person was simply infected again. That could happen if the antibodies generated don't last long.
Will the virus go away with the weather/summer?
Quite likely, yes. Cold and flu viruses don't do well outside in summer weather. (For influenza, the warm weather causes the viral envelope to become a liquid, and it can no longer protect the virus.) That's why cold and flu season is always during the late fall and winter. However, some experts think that it is a "false hope" that the coronavirus will disappear during the summer. We'll have to wait and see.
And will it come back in the fall/winter?
That's a likely outcome. Again, we'll have to wait and see. Some epidemiologists think that COVID-19 will become seasonal like influenza.
Does dry or humid air make a difference?
Flu viruses prefer cold, dry weather. That could be true of coronaviruses, too.
What is the incubation period?
According to the World Health Organization, it's about 5 days. But it could be anywhere from 1 to 14 days.
Should you worry about sitting next to asymptomatic people on a plane or train?
It's not possible to tell if an asymptomatic person is infected or not. That's what makes asymptomatic people tricky. Just be cautious. If you're worried, treat everyone like they might be infected. Don't let them get too close or cough in your face. Be sure to wash your hands.
Should you cancel air travel planned in the next 1-2 months in the U.S.?
There are no hard and fast rules. Use common sense. Avoid hotspots of infection. If you have a trip planned to Wuhan, you might want to wait on that one. If you have a trip planned to Seattle and you're over the age of 60 and/or have an underlying health condition, you may want to hold off on that, too. If you do fly on a plane, former FDA commissioner Dr. Scott Gottlieb recommends cleaning the back of your seat and other close contact areas with antiseptic wipes. He also refuses to take anything handed out by flight attendants, since he says the biggest route of transmission comes from touching contaminated surfaces (and then touching your face).
There have been reports of an escalation of hate crimes towards Asian Americans. Can the microbiologist help illuminate that this disease has impacted all racial groups?
People might be racist, but COVID-19 is not. It can infect anyone. Older people (i.e., 60 years and older) and those with underlying health conditions are most at risk. Interestingly, young people (aged 9 and under) are minimally impacted.
To what extent/if any should toddlers -- who put everything in mouth -- avoid group classes like Gymboree?
If they get infected, toddlers will probably experience only a mild illness. The problem is if the toddler then infects somebody at higher risk, like grandpa or grandma.
Should I avoid events like concerts or theater performances if I live in a place where there is known coronavirus?
It's not an unreasonable thing to do.
Any special advice or concerns for pregnant women?
There isn't good data on this. Previous evidence, reported by the CDC, suggests that pregnant women may be more susceptible to respiratory viruses.
Advice for residents of long-term care facilities/nursing homes?
Remind the nurse or aide to constantly wash their hands.
Can we eat at Chinese restaurants? Does eating onions kill viruses? Can I take an Uber and be safe from infection?
Yes. No. Does the Uber driver or previous passengers have coronavirus? It's not possible to tell. So, treat an Uber like a public space and behave accordingly.
What public spaces should we avoid?
That's hard to say. Some people avoid large gatherings, others avoid leaving the house. Ultimately, it's going to depend on who you are and what sort of risk you're willing to take. (For example, are you young and healthy or old and sick?) I would be willing to do things that I would advise older people avoid, like going to a sporting event.
What are the differences between the L strain and the S strain?
That's not entirely clear, and it's not even clear that they are separate strains. There are some genetic differences between them. However, just because RNA viruses mutate doesn't necessarily mean that the virus will mutate to something more dangerous or unrecognizable by our immune system. The measles virus mutates, but it more or less remains the same, which is why a single vaccine could eradicate it – if enough people actually were willing to get a measles shot.
Should I wear disposable gloves while traveling?
No. If you touch something that's contaminated, the virus will be on your glove instead of your hand. If you then touch your face, you still might get sick.