How dangerous is the Covid-19 Delta variant?
A Covid-19 variant that likely wreaked havoc during Indias second wave has now spread to 80 countries. 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 cases there. In the US, too, the number of Delta variant cases are rapidly rising, up from 10% of the total Covid-19 cases last week to 20% this week. According to a Financial Times analysis, the delta variant accounts for more than a third of new cases each day in the US. This surge has led Dr Anthony Fauci, chief medical advisor to the White House, to label the variant as the greatest threat to the countrys 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 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 variants on WHOs radar  Maria Van Kerkhove, the WHOs technical lead for Covid confirmed that the delta variant has now spread to 92 countries. Thus far, there are four variants of concern flagged by the World Health Organization (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 parametersincreased transmissibility, more virulence, and decreased effectiveness of public health measuresto determine its seriousness. The delay is also because there wasnt enough genome sequencing data coming from India during its brutal second wave. Now, data from the Public Health England (PHE), the UK governments health executive arm, have given scientists and public health experts around the world some ability to make sense of this Covid-19 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 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 concernAlpha (first identified in the UK), Beta (South Africa), Gamma (Brazil) and Deltaare different from all other countless variants for this very reason. The Delta variant has certain significant mutations in the spike protein of the virusthe pointy elements that give it the shape of a crown (which is why its 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 variantsuch as the E484Q, L452R, and P614Rmake 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 bodys 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 the other viral mutations. Those with the Delta variant often complain of headaches, sore throat, and a runny nose, replacing cough and loss of taste of smell as the most common symptoms. 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. Its 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 antibodieseither through infection or vaccinationto 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. It is reasonably certain that the Delta variant also exhibits some immune escape, although estimates vary as to the extent, explains Dr Gautam Menon, professor at the departments of physics and biology at Ashoka University in Sonipat. 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, Pfizers 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, the Delta variant could lead to a spike in cases. The Delta variant has developed a new mutation of a type that was first found in the Beta variant. The new variantwhich is being labeled Delta Plus, though not officially by the WHO yetadditionally 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 treatmentslike the one given to former US president Donald Trumpineffective 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. 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 nine countries, including the UK, US, China, and Japan.