COVID-19 vaccines

FETHI BELAID/AFP via Getty Images

With the United States still well short of reaching herd immunity against COVID-19, concern is growing over a new variant of the virus that researchers now believe is between 30 percent and 100 percent more transmissible than the previously most dominant variant. "The best estimate at the moment is this [new] variant may be 60 percent more transmissible than the Alpha ['U.K.'] variant," epidemiologist Neil Ferguson told The Guardian.

The new variant, known as the Delta variant, accounted for around 60 percent of cases in Delhi in April, at a time when one in every three samples tested in the city were coming back positive for COVID-19, India's Tribune reports. But while the Delta variant was first identified in India, it has now spread to 62 countries; on Friday, authorities in Australia's Victoria state confirmed the variant is a factor in their new Melbourne outbreak. The variant has also been found in the U.S.

Though research is ongoing, there is not yet any sign that the Delta variant is more deadly than other variants. Still, that doesn't mean it's less dangerous; as Zeynep Tufekci wrote for The New York Times in an article titled "COVID's deadliest phase may be here soon" on May 28, "A variant with higher transmissibility is a huge danger to people without immunity either from vaccination or prior infection, even if the variant is no more deadly than previous versions of the virus … A more transmissible variant can burn through such an immunologically naïve population very fast." 

U.K. researchers recently found that two doses of a COVID-19 vaccine appear to be slightly less effective against the Delta variant (providing 81 percent protection, versus the 87 percent against the dominant U.K. variant). But single doses of a vaccine were particularly ineffective, with just 33 percent effectiveness. "If that is accurate," writes Intelligencer, "it means that [the Delta variant] may be the variant that currently poses the biggest threat to partially vaccinated populations worldwide."