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Experts say COVID-19 vaccines so far have been effective against the Delta variant. Halfpoint Images/Getty Images
  • Experts say the COVID-19 Delta variant poses a threat in the United States because it is more contagious than other strains and produces more serious symptoms.
  • They add that although the current vaccines are effective against the variant, the strain will have more chances to mutate as unvaccinated people contract the virus.
  • The most common symptoms for the Delta variant are fever, headache, sore throat, and runny nose.

All data and statistics are based on publicly available data at the time of publication. Some information may be out of date. Visit our coronavirus hub and follow our live updates page for the most recent information on the COVID-19 pandemic.

Many states have relaxed COVID-19 restrictions, allowing people in the United States to return to a semblance of life before the pandemic.

Still, a decrease in vaccination levels coinciding with the explosive spread of a new coronavirus variant has some health experts concerned about the country’s pandemic endgame.

The Delta variant, also known as B.1.617.2, was first detected in India but has since surfaced in more than 70 countries, according to the World Health Organization (WHO).

In the United States, the variant accounts for more than 6 percent of sequenced virus samples, according to data from the Centers for Disease Control and Prevention (CDC). This is a jump from about 1 percent a month ago.

This variant not only spreads more easily than earlier strains but may also cause more severe disease. This is particularly worrisome for unvaccinated people and those who have a weaker immune response to the virus.

Doctors in China find that as the Delta variant spreads throughout the country, people have different and more severe symptoms than reported earlier in the pandemic, reports The New York Times.

Fevers are common. The level of virus in the body rises higher than previously seen during the pandemic. And more people are becoming severely ill within 3 or 4 days.

In the United Kingdom, where the Delta variant makes up 91 percent of new cases, one study found that the most reported symptoms were headache, sore throat, and runny nose.

For younger people, this might feel like just a bad cold. But they could still spread the virus to others who are more at risk of severe illness, including those not yet fully vaccinated.

Even people with an asymptomatic infection can pass on the virus to others.

As scientists collect more data, a clearer picture of the symptoms Delta causes will emerge.

People should be on alert for other symptoms of coronavirus infection, such as cough, shortness of breath, headache, fatigue, or loss of sense of taste or smell.

The United States and the United Kingdom have fully vaccinated about 43 percent of their populations. But as the Delta variant has become more common in the United Kingdom in recent weeks, the country has seen a spike in COVID-19 cases.

A similar spike in cases was seen in India as the Delta variant spread widely. Experts say this is due to this variant being more transmissible.

U.K. Health Secretary Matt Hancock said this past weekend that the Delta variant is around 40 percent more transmissible than the Alpha variant, which was previously dominant in the country, reports BBC News.

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said at a White House COVID-19 briefing this past week that studies support this idea.

“Clearly now [the Delta variant’s] transmissibility appears to be greater than the wild type,” said Fauci, referring to the original strain of the virus that emerged at the start of the pandemic.

Early evidence suggests the Delta variant may increase the risk of hospitalization compared to the Alpha variant, Public Health England (PHE) reported June 10.

One analysis by PHE of more than 38,000 COVID-19 cases in England found that people with the Delta variant were 2.61 times more likely to be hospitalized than those with the Alpha variant.

Fauci echoed the PHE’s concerns about the Delta variant, saying, “It may be associated with an increased disease severity, such as hospitalization risk, compared to Alpha.”

PHE also found that in some areas where the Delta variant was increasing, hospital visits and admissions were “predominantly in unvaccinated individuals.”

This suggests that even with this variant, full vaccination offers protection against more severe disease and hospitalization.

For a two-dose vaccine such as Pfizer-BioNTech or Moderna-NIAID, full vaccination is at least 14 days after the second dose. For a single-shot vaccine such as Johnson & Johnson, full vaccination is at least 14 days after the dose.

There is other evidence that the COVID-19 vaccines work against the Delta variant.

A study published June 10 in the journal Nature found that 20 people who had received two doses of the Pfizer–BioNTech vaccine had enough antibodies in their blood to neutralize several variants, including Delta.

This suggests that the vaccine would provide adequate protection against the Delta variant, the authors wrote, although they say real-world studies are needed to know for certain.

Other research emphasizes the importance of full vaccination, especially when the Delta variant is spreading widely in the community.

Researchers at the Francis Crick Institute and National Institute for Health Research (NIHR) UCLH Biomedical Research Centre reported in The Lancet that people were less likely to develop after a single dose of the Pfizer-BioNTech vaccine an adequate immune response to the Delta variant, compared with the original strain.

Real-world data supports the need to get as many people their second dose as soon as possible.

A pre-print study released by PHE on May 22 found that two doses of the Pfizer-BioNTech vaccine were 88 percent effective against symptomatic infection with the Delta variant than 93 percent for the Alpha variant.

However, one dose was only 33 percent effective against symptomatic infection with the Delta variant versus 50 percent for the Alpha variant.

“A single dose of the mRNA vaccines clearly conveys insufficient protection against the Delta variant,” said Dr. Stanley H. Weiss, professor of medicine at Rutgers New Jersey Medical School and a professor of biostatistics and epidemiology at Rutgers School of Public Health. “But current data suggests that you have pretty good protection against the Delta strain after complete vaccination.”

Most at risk from the Delta variant are people who are not fully vaccinated and those who don’t have a robust immune response to vaccination, such as older adults and the immunocompromised.

Weiss says these people, even when fully vaccinated, may want to continue taking precautions when in public settings, where others may have the virus.

“Because someone over 80 or who is immunosuppressed is at particularly high risk for progression to significant disease or death, we should be very careful with those groups,” Weiss told Healthline.

Some experts see the United Kingdom as a cautionary tale for the United States.

“This is a situation, the way it was in England, where they had a B.1.1.7 dominant and then the [B.1.] 617 took over. We cannot let that happen in the United States,” said Fauci.

With the rapid rise of the Delta variant in the United Kingdom, British Prime Minister Boris Johnson is expected to postpone the end of COVID-19 restrictions by several weeks.

This is “such a powerful argument … to get vaccinated,” Fauci said. “Particularly if you’ve had your first dose, make sure you get that second dose. And for those who have not been vaccinated yet, please get vaccinated.”

Much of the focus right now is on the existing variants. But the more that the novel coronavirus is allowed to spread, the more chances it has to mutate.

“We can expect that there will be other variants that will arise, spread, and become of concern,” said Weiss.

He says that’s why all countries need to have equal access to the vaccines and increase vaccine uptake in those parts of the United States with low vaccination rates.

“Those parts of the world where the virus is spreading could become hotbeds for creating new variants that could pose a risk for the rest of the world,” said Weiss.