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How dangerous is the Covid-19 delta variant?

A doctor checks an X-ray of a patient suffering from the coronavirus disease (COVID-19) inside a COVID-19 ward of a hospital in New Delhi
Reuters/Danish Siddiqui
Variant of global concern.
  • Manavi Kapur
By Manavi Kapur

Reporter

Published Last updated on

Delta variant, a strain of Covid-19 that likely wreaked havoc during India’s second wave has been identified in at least 85 countries. According to the World Health Organization (WHO), the delta covid variant is the most transmissible of all the variants identified so far. Acknowledging the contagious nature of the delta Covid-19 variant that was first identified in India, the WHO on June 25 urged vaccinated people to continue wearing masks.

The delta variant, or B.1.617.2, which was first identified in India in October 2020, has now become the dominant strain in the UK, currently accounting for more than 90% of coronavirus cases there. Meanwhile, in the US, the delta variant accounts for more than a third of new cases as per a Financial Times analysis. The former commissioner of the US Food and Drug Administration, Dr. Scott Gottlieb told CBS News’ Face the Nation that the United States is likely to witness “very dense outbreaks” due to the delta variant.

The US Centers for Disease Control and Prevention (CDC) estimates that delta accounted for 20.6% of all Covid-19 cases between June 5 and June 19.

This surge has led Dr. Anthony Fauci, chief medical advisor to the White House, to label the variant as the “greatest threat” to the country’s attempt to eradicate Covid-19.

Both the UK and US have high vaccination rates, and it remains to be seen whether their populations are protected against this Covid strain. But in much of the rest of the world, where Covid-19 vaccines have not been administered at the same level, the concerns are even greater.

Covid delta variant on WHO’s radar

On June 25, the World Health Organization’s Dr. Maria Van Kerkhove in a press conference said that the delta variant is a dangerous virus. “It is more transmissible than the Alpha variant, which was extremely transmissible across Europe, across any country that it entered. The Delta variant is even more transmissible,” she explained during the conference.

Thus far, there are four “variants of concern” flagged by the WHO and seven “variants of interest.” Despite the strain being identified last year, the delta variant was tagged as a variant of concern only on May 11. This is because the WHO uses three parameters—increased transmissibility, more virulence, and decreased effectiveness of public health measures—to determine its seriousness.

The delay is also because there wasn’t enough genome sequencing data coming from India during its brutal second wave. Now, data from the Public Health England (PHE), the UK government’s health executive arm, have given scientists and public health experts around the world some ability to make sense of this Covid-19 variant.

What is the delta variant?

When Covid-19 infections broke out in Wuhan, China, that first strain was a “wild type” virus. This was the strain used by scientists across the world to develop testing kits, treatment plans, and even Covid vaccines.

It is in the nature of viruses to mutate, and it did. But not all mutations are serious, and usually do not require countries to reimagine their public health measures.

The variants of concern—Alpha (first identified in the UK), Beta (South Africa), Gamma (Brazil), and Delta—are different from all other countless variants for this very reason.

The delta variant has certain significant mutations in the spike protein of the virus—the pointy elements that give it the shape of a crown (which is why it’s called the coronavirus). These spikes are like hooks that have to find the receptors in a human cell to link with. Studies have shown that these spikes hook onto receptors called ACE-2. Once these spike proteins can unlock the cells, the infection spreads by replicating the genetic code of the virus.

Some key mutations in the delta variant—such as the E484Q, L452R, and P614R—make it easier for the spikes in the virus to attach to ACE-2 receptors. This means it can infect and replicate faster, and even evade the body’s natural disease-fighting immunity more efficiently.

The spike protein mutations make the delta variant the “fastest and fittest” variant yet, according to the WHO. The disease caused by this variant might also exhibit different symptoms than other viral mutations. Those infected with delta variant develop symptoms such as headaches, sore throat, and a runny nose, replacing cough and loss of taste or smell like the most common symptoms.

Is the delta variant more transmissible?

“Most studies indicate delta is 50-60% more transmissible than the Alpha variant,” says Dr. Bhramar Mukherjee, associate director for quantitative data sciences at the University of Michigan Rogel Cancer Center. “The Alpha variant itself was nearly 50-60% more transmissible than the original strain.”

This, according to Mukherjee, implies that if the reproduction number for the original strain was around 2.4-2.6, the one for Alpha is 3.6-4.2, and for delta, it is 5.6-6.7. In layman terms, if a person infected with the original strain could infect nearly two people, a person with the Alpha variant could infect four people. With delta, one person could infect nearly seven other people. It’s important to remember that these are averages, not absolute numbers; one delta carrier might infect zero people, or 25.

Its higher reproduction number is likely why entire families in crowded Indian cities like Delhi and Mumbai were infected together. It would also explain the tsunami-like surge of cases in the country in April and May.

The other consequence of a higher reproduction number (denoted as R in epidemiological data) in an epidemic is that it increases the threshold for herd immunity. That is, more people will need to have the antibodies—either through infection or vaccination—to be protected as a community against the delta variant. “With an R of 2.5, the threshold for herd immunity is 60%, but with an R of 6, it is 83%,” explains Mukherjee.

Do vaccines work against the delta variant?

According to the CDC, studies show that the currently authorized vaccines which include Pfizer-BioNTech, Moderna, and Johnson&Johnson or Janssen work on the circulating variants.

Dr. Gautam Menon, professor at the departments of physics and biology at Ashoka University in India said, “It is reasonably certain that the delta variant also exhibits some immune escape, although estimates vary as to the extent.” For instance, single doses of Covid-19 vaccines, according to data from the UK, are only 33% efficacious against the disease.

But there is hope that those who are fully vaccinated are reasonably protected against serious disease. According to data from PHE, Pfizer’s mRNA vaccine is 96% effective, and the AstraZeneca vaccine 92% effective against hospitalizations after two doses. These, PHE says, are comparable to efficacy against the Alpha variant.

This also means that getting a large part of the population fully vaccinated is crucial for countries where the delta variant is prevalent. For countries like the US, where nearly half the population is fully vaccinated, scientists suspect a varied impact of the delta variant. “I would expect some breakthrough infections and transmission happening even in highly vaccinated areas in the US, but would not expect a spike in hospitalizations and deaths,” Mukherjee says.

“We cannot be complacent with a large percentage only partially vaccinated, dropping masks and Covid-appropriate behaviors,” she adds. “We need full vaccination for a large fraction to fight the delta variant.” She also expects that in pockets of the US with lower vaccine coverage, cases of delta variant could rise.

Experts from WHO reiterated that the delta variant is spreading rapidly among unvaccinated populations. However, the health agency quickly noted that “vaccines are effective at preventing severe disease and death, including against the delta variants.

Can masks keep the delta variant in check?

Public health experts are investigating whether booster shots of vaccines will be needed to protect the population against the new variant.

Hence, the WHO is once again highlighting the need to wear masks. “Vaccine alone won’t stop community transmission,” said Mariangela Simao, the WHO’s assistant director-general for access to medicines and health products, during a briefing at the organization’s headquarters in Geneva. “People need to continue to use masks consistently, be in ventilated spaces, [practice] hand hygiene, [maintain] physical distance, avoid crowding,” she said.

Although Covid cases in the US have been steadily declining as vaccination rates are going up, it might be reaching an impasse. Joe Biden had set a target of immunizing 70% of adult Americans by July 4, but the country will fall short of it, reaching 67% of all eligible adults. Some 20% Americans say they don’t want to get the vaccine.

What is the delta plus variant?

The delta variant has developed a new mutation of a type that was first found in the Beta variant. The new variant—which is being labeled delta plus, though not officially by the WHO yet—additionally has the K417N mutation in its spike protein, which is associated with increased immunity escape.

Shahid Jameel, a top virologist in India, has said that delta plus could also render cocktail antibody treatments—like the one given to former US president Donald Trump—ineffective in fighting the disease. This variant could also potentially lead to vaccines being less effective. India has officially flagged delta plus a “variant of concern,” though after a great deal of indecision.

Menon says the delta plus variant is not a cause for worry yet but would be “if it began to replace the existing variants.” “Currently, there is no evidence that this is the case,” he says, “so there is no cause for immediate worry, but this may change and we should be watchful for this.”

Mukherjee warns that India, where 40% of the population is below the age of 17 and not eligible for vaccines, needs to adhere to strong public health interventions to control the coronavirus pandemic. Besides scaling up vaccinations, she suggests better studies around the variants, an area where India has been particularly slow. “We need to study properties of these variants: what the clinical manifestations are, whether our diagnostic tests work well to detect them, whether treatments work well.”

The delta plus variant has now been detected in at least nine countries, including the UK, US, China, and Japan.

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