What you need to know about the highly contagious coronavirus delta variant

The highly transmissible coronavirus variant called delta is present in all 50 states and is already dominant in many parts of the United States.

Modeling shows the new variant now accounts for 51.7% of all infections in this country, five times the prevalence four weeks earlier, according to the Centers for Disease Control and Prevention. The latest estimates show delta has overtaken alpha, the variant first identified in the United Kingdom which quickly spread throughout the world, including the United States.

Here are answers to commonly asked questions about the delta variant and how to protect yourself.

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What is the delta variant?

The delta variant, also known as B. 1.617, was first detected last year in India, where it has been ravaging the nation, and has since spread to dozens of other countries, where it is upending plans for a return to normalcy.

Delta actually has several lineages with slightly different sets of mutations. One of those - B. 1.617.2 - is also now the dominant coronavirus strain in the United Kingdom, where it accounts for the vast majority of all covid-19 cases in that nation.

Experts describe delta as the most “fit” variant of all the coronavirus mutations. That means it is likely to outcompete other variants to infect more people with covid-19, the disease caused by the virus, said Monica Gandhi, an infectious-diseases expert at the University of California at San Francisco. “It’s the one that is most likely to latch onto cells in a host, and it attacks that host better than the other variants because it can replicate itself better.”

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Why is the delta variant a concern?

Early research suggests that delta is about 50% more contagious than the alpha variant, which became the predominant strain in the United States during the spring. Alpha was already about 50% more transmissible than the original strain of the coronavirus first identified in Wuhan, China in late 2019.

Although there is compelling evidence that the delta variant is more transmissible, there is limited data on whether it is more likely to result in a severe illness.

Public Health England found that the variant may be associated with a higher risk of hospitalization, and some early research from Scotland suggests people are at about twice the risk of hospitalization with covid-19 infections from the delta variant than from alpha - with the unvaccinated at greatest risk.

But experts caution there is no clear evidence that delta is more likely to cause severe disease. Hospitals serving areas where delta is surging have reported admitting more young and middle-aged covid patients, but note that may be because they are less likely to be vaccinated.

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How effective are the vaccines against the variant?

Early data suggests that all three vaccines authorized in the United States offer strong protection against severe disease and death from the delta variant, although they may offer less robust protection against minor to moderate infections.

“I think this is a really important point because that’s our primary goal with our vaccination effort - to prevent severe disease, to prevent hospitalization, to prevent deaths,” said William Moss, a professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health.

In the case of the two-dose messenger RNA vaccines, both shots are needed to mount a strong response against delta. Research from Public Health England (PHE) recently showed that the Pfizer-BioNTech was 33% effective against symptomatic infection from the delta variant after the first shot of the two-shot regimen, but 88% effective after the second one.

In terms of preventing hospitalizations from delta, another PHE paper suggested that the Pfizer-BioNTech vaccine was 94% effective after the first shot and 96% effective after the second.

Experts said because the Moderna vaccine is comparable to Pfizer, researchers could extrapolate that it would offer similar protection.

As for the Johnson & Johnson shot, one small study showed that people who took the vaccine mounted a strong antibody response against the variant, the company told The Washington Post.

Some researchers believe that the Johnson & Johnson vaccine may end up showing similar results to the AstraZeneca vaccine, which was included the PHE studies and found to be 60% effective against symptomatic disease and 92% effective against hospitalization after both doses. The AstraZeneca vaccine has not been approved for use in the United States.

“Vaccination is your force field; that is the best precaution you can take,” Gandhi said.

How will the delta variant affect the U.S.?

With more than 150 million Americans now inoculated against the coronavirus, the delta variant is not expected to cause massive outbreaks across the entire United States. Instead, health experts anticipate it will cause surges in communities where vaccination rates are lower, posing the most serious risk to those who are older, sicker and unvaccinated.

“We’re going to have to face it throughout the United States,” said Eric Topol, a professor of molecular medicine and executive vice president at the Scripps Research Institute. “So far, it’s at a low level in terms of increase in cases, but we don’t know where it’s headed.”

Topol said delta is already spreading through states such as Nevada, Missouri, Arkansas, Utah and Wyoming, which are more vulnerable because they have had fewer cases of covid-19 and also fewer vaccinations, meaning they do not have as much natural and vaccine-induced immunity.

States with high vaccination rates like Connecticut, Massachusetts and Vermont have “a delta wall,” he said.

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Anthony Fauci, the nation’s leading infectious-diseases expert, recently said he is “very concerned” about the variant because it could lead to “two Americas” - one largely protected due to high vaccination rates and the other experiencing surges due to with low vaccination rates.

“When you have such a low level of vaccination superimposed upon a variant that has a high degree of efficiency of spread, what you are going to see among undervaccinated regions - be that states, cities or counties - you’re going to see these individual types of blips. It’s almost like it’s going to be two Americas,” he said.

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Do symptoms from delta infections differ from infections from other strains of the coronavirus?

There is little research on this but some people have reported symptoms such as a headache, sore throat and runny nose, without the hallmark covid-19 signs such as loss of taste and smell.

Will booster shots be needed?

Currently, there is no evidence booster shots are necessary to buttress any of the vaccines approved by the Food and Drug Administration, and federal health officials do not recommend them at this time.

Health experts said the time to start thinking about boosters would be if the delta variant, or any other variant, begins causing significant breakthrough infections within heavily vaccinated communities. “That would be a red flag that we need boosters or new vaccines to target the delta variant,” Moss said.

[Pfizer to seek authorization for 3rd vaccine dose to boost immunity over time]

What else can people do to protect themselves?

Although the CDC no longer recommends masking for people who are fully vaccinated, health experts said it may make sense for some people depending on their circumstances. Those who are living in areas where vaccination rates are low and delta cases are high may want to continue covering their faces, particularly in high-risk settings such as indoor gatherings, large crowds, or places such as senior living facilities where the consequences of transmission could be grave.

The World Health Organization is still urging people around the world to mask up. Mariangela Simao, WHO’s assistant director general for access to medicines and health products, recently told reporters, “People cannot feel safe just because they had the two doses. They still need to protect themselves.”

Gandhi said that recommendation makes sense coming from WHO, which is dealing with very mixed populations - many with high amounts of circulating virus, low vaccination rates and less effective vaccines. Only about 11% of the world’s population has been fully inoculated against the virus.

“The likelihood of getting a breakthrough infection with any variant is not just dependent on your vaccination status but the amount of virus you’re seeing circulating in your community,” she said. “It’s why health care workers in India, even though they were fully vaccinated, still had breakthrough infections because they were seeing so much virus.”

What about people who are immunocompromised?

Vaccination is still the top recommendation to protect against the virus, including the delta variant, although not all immunocompromised people may mount a robust response. But others will build immunity from the shots and there appears to be no harm from getting immunized, said William Schaffner, medical director of the National Foundation for Infectious Diseases.

Beyond that, individuals with compromised immune responses should practice social distancing, mask-wearing and avoid crowds, particularly indoors - “those things continue to pertain to these highly susceptible people,” he said.

Schaffner, a professor of infectious diseases and preventive medicine at Vanderbilt University, said it is also important for immunocompromised people to get tested if they experience symptoms, especially as the new influenza season rolls around, so they can get treated appropriately - either for flu or covid-19. In some cases, for example, antiviral medications may be used to treat influenza and monoclonal antibodies for covid-19, which can reduce the risk of hospitalization and death when used early in the course of the disease.

What about the risk to children and how can parents protect them?

There is no indication the delta variant is more virulent if it infects children, said Paul Offit, a pediatrician and the director of the Vaccine Education Center at Children’s Hospital of Philadelphia.

However, since it is more contagious than earlier variants, children are at somewhat greater risk of infection. Those who are 12 and older are eligible for vaccines and federal health officials recommend they be immunized for greater protection.

For children 11 and younger, Offit recommends that parents make sure their unvaccinated children wear masks if they are in public spaces indoors.

The bottom line is that the people need to take measures to protect themselves and their loved ones against the delta variant.

“If you haven’t had covid, you’re not vaccinated and you’re not wearing a mask, you’re basically asking for delta trouble. It’ll find you. It’s the most efficient form of the virus for finding hosts, by far. If you’re not vaccinated, a mask is important right now,” Topol said.

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The Washington Post’s Ben Guarino contributed to this report.