A coronavirus variant that was first found in India is now the dominant strain circulating in the U.S., according to the Centers for Disease Control and Prevention
The highly transmissible strain, known as the delta variant, is responsible for more than half of the country’s new coronavirus infections as of early July, according to a CDC estimate. The first U.S. case of the variant was documented in March, and the percentage of delta cases has been roughly doubling every two weeks.
Public health officials have warned that the delta variant could spread easily among unvaccinated populations. The head of the Centers for Disease Control and Prevention recently said that about 1,000 counties in the U.S. have vaccination coverage rates of under 30%.
Those parts of the country could see more infections as the delta variant takes hold.
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“Unfortunately, I do expect that we will see some surges, but I do not think they will be nationwide anymore because we do have several states that are clearly on track, that have already achieved somewhat good vaccination,” says Amber D’Souza, a professor of epidemiology at Johns Hopkins Bloomberg School of Public Health.
And while the World Health Organization has suggested that fully vaccinated people should still practice mask-wearing in areas of high transmission, the CDC has said its mask guidance remains unchanged in the face of the delta variant.
Why Is the Delta Variant Concerning?
WHO has called the delta strain “the most transmissible of the variants identified so far.”
“That means that each infected person is on average infecting more people, and because of this, the delta strain outcompetes the other strains and is becoming the dominant strain that we see in the U.S. and elsewhere,” D’Souza says.
Research has suggested that the delta variant could be between 40-60% more transmissible than the alpha strain first found in the U.K. With less than half of the U.S. population fully vaccinated, there is ample opportunity for the delta variant to spread.
One study out of Scotland suggested that the delta variant nearly doubled the risk of hospitalization compared to the alpha strain. But experts warn that data is still evolving and the picture could be different in the U.S.
It’s also too soon to say whether the variant is more deadly than the original strain or the other variants or whether protection from previous infections from another strain will stand up to the delta strain.
“All of the people who aren’t vaccinated because they said they already had [COVID-19] and they’re actually protected, it’ll be really interesting to see their protection in the coming months and if that actually holds true,” says Marilyn Bulloch, an associate clinical professor at Auburn University’s Harrison School of Pharmacy.
Do Vaccines Work on the Delta Strain?
All three coronavirus vaccines authorized for emergency use in the U.S. appear to work on the delta variant, though with slightly reduced efficacy.
“The fact that these amazing vaccines have been able to hold up to the mutations of the virus is such great news,” D’Souza says.
Johnson & Johnson recently said that its vaccine generated a “strong, persistent” immune response to the rapidly spreading delta variant in a lab study, possibly diminishing concerns among recipients of the potential need for a booster shot. Moderna and Pfizer have also said they expect their vaccines to work on the variant, though with slightly reduced efficacy.
But a person who has received just a single shot of a two-dose vaccine has “barely” any protection against the delta variant, according to a report published this week, highlighting the importance of finishing the recommended vaccine dosage.
Recent data out of Israel caused a stir when it suggested that Pfizer’s efficacy against preventing infection and symptomatic COVID-19 fell to 64% on the delta variant. However, the shot was still 94% effective at preventing severe illness. Some public health experts questioned the study, saying more data is needed.
“It’s really hard to know exactly how the protection is going to be until we get data from America,” Bulloch says.[
Still, the most important factor from a public health point of view is protection from hospitalization and death, and the vaccines are likely to continue to have a strong efficacy in those areas even when up against the variant.
Another factor that could keep U.S. coronavirus deaths and hospitalizations down is the high rate of vaccination among U.S. adults 65 and older. According to the CDC, nearly 79% of that population is fully vaccinated.
“We did see high uptake of the vaccine among older individuals across all states, and that will protect us against the highest mortality rates because we really did achieve good coverage in our senior citizens,” D’Souza says.
But there are still roughly 150 million Americans who haven’t received even one vaccine dose.
“It’s important while we celebrate the tremendous accomplishments over these past few months in the vaccine rollout, to remember that the battle is not yet done and most areas of the country do not yet have high enough levels of protection to prevent a resurgence,” D’Souza says.
What Is Delta Plus?
The delta plus variant is a sublineage of the delta variant that has an additional mutation.
Authorities in India have called it a “variant of concern,” but WHO hasn’t matched that designation yet.
WHO recently told Reuters that the delta plus variant “does not seem to be common, currently accounting for only a small fraction of the delta sequences.” But it added that “delta and other circulating variants of concern remain a higher public health risk, as they have demonstrated increases in transmission.”
There is concern that the mutation could lead the delta plus variant to be more transmissible. Studies are ongoing to test vaccine effectiveness against the strain.[
“I think our alarm about the delta plus variant should just be that this virus is continuing to circulate and mutate as we would expect, and it makes our fight that much harder to contain the spread of this infection,” D’Souza says.
Where Have Delta and Delta Plus Been Found?
The delta strain has been found in all 50 U.S. states. It’s been documented in over 100 countries.
According to CDC data, the delta strain represented more than 80% of cases across Iowa, Kansas, Missouri and Nebraska from June 20-July 3.
Meanwhile, the delta plus strain has been documented in over 10 countries, including the U.S.
Experts warn that worldwide vaccination rates need to dramatically increase in order to prevent more variants from arising. Rates still need to increase in the U.S., as well.
“We can’t stop this pandemic just by focusing on the U.S., but what we can do is protect ourselves as a nation by achieving high vaccination,” D’Souza says.