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A top World Health Organization official estimated Monday that COVID-19 vaccination coverage of at least 80% is needed to significantly lower the risk that “imported” coronavirus cases like those linked to new variants could spawn a cluster or a wider outbreak. Dr. Michael Ryan, WHO’s emergencies chief, told a news conference that ultimately, “high levels of vaccination coverage are the way out of this pandemic.” (Keaten, 6/7)

The coronavirus variant driving India’s devastating Covid-19 second wave is the most infectious to emerge so far. Doctors now want to know if it’s also more severe. Hearing impairment, severe gastric upsets and blood clots leading to gangrene, symptoms not typically seen in Covid patients, have been linked by doctors in India to the so-called delta variant. In England and Scotland, early evidence suggests the strain -- which is also now dominant there -- carries a higher risk of hospitalization. (Shrivastava, 6/7)

The coronavirus variant labeled “delta” was first recorded in India, where a slow vaccination drive and complacency about pandemic rules helped spark a record-breaking surge in cases this spring. Since then the variant has spread, and as new cases rise in Britain, it has become dominant, despite one of the most successful vaccination programs anywhere. Its newfound prevalence could upend plans for a return to normalcy. (Taylor, 6/7)

In December, British researchers discovered that a new variant was sweeping through their country. When it arrived in other countries, the variant, now known as Alpha, tended to become more common in its new homes as well. By April, it had become the dominant variant in the United States, and it has remained so ever since. Alpha’s swift success has left scientists wondering how the variant conquered the world. A new study points to one secret to its success: Alpha disables the first line of immune defense in our bodies, giving the variant more time to multiply. (Zimmer, 6/7)

Any diagnostic test worth its salt has precision on its side. It can pinpoint the presence of this condition, but not that one; it can, when used for an infectious disease, distinguish between microbes that look very much the same. For most of the pandemic, that exactness has been a major asset for the hundreds of tests that detect SARS-CoV-2. But the discerning nature of most tests has also opened up a weak point for the coronavirus to exploit. With the virus mutating into new and concerning variants, a few of the tests designed to recognize its original iteration are now getting duped. What was once a singular target has split itself off into many, many bull’s-eyes, each a little different from the next, and we’re having trouble taking aim. (Wu, 6/7)