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‘Dealing with a different beast’: Why Delta has doctors worried


Escape artist

Recent studies show that Delta is also able to escape antibodies made in response to vaccination more effectively than the Alpha, or B.1.1.7 strain. The effect was more pronounced in older adults, who tend to have weaker responses to vaccines in general.

This evasion of the immune system is particularly problematic for people who are only partially vaccinated. Data from the United Kingdom show that a single dose of vaccine is only about 31% effective at preventing illness with Delta, and 75% effective at preventing hospitalization.

After two doses, the vaccines are still highly effective — even against Delta — reaching 80% protection for illness, and 94% for hospitalization, which is why U.S. officials are begging people to get both doses of their shots, and do it as quickly as possible.

Finally, the virus’s ability to form syncytia may leave greater damage behind in the body’s tissues and organs.

“Especially in the lungs,” Dr. Kadkhoda said. The lungs are very fragile tissues. Their tiny air sacs — the alveoli — are only a single-cell thick. They have to be very thin to exchange oxygen in the blood.

“Any damage like that can severely affect any oxygen exchange and the normal housekeeping activities of that tissue,” he said. “In those vital organs, it may be very problematic.”

The research is still early, but studies in animals and cell lines are backing up what doctors say they are seeing in hospitalized patients.

A recent preprint study from researchers in Japan found that hamsters infected with Delta lost more weight — a proxy for how sick they were — compared with hamsters infected with an older version of the virus. The researchers attribute this to the viruses› ability to fuse cells together to form syncytia.

Another investigation, from researchers in India, infected two groups of hamsters — one with the original “wild type” strain of the virus, the other with the Delta variant of the new coronavirus.

As in the Japanese study, the hamsters infected with Delta lost more weight. When the researchers performed necropsies on the animals, they found more lung damage and bleeding in hamsters infected with Delta. This study was also posted as a preprint ahead of peer review.

German researchers working with pseudotyped versions of the new coronavirus — viruses that have been genetically changed to make them safer to work with — watched what happened after they used these pseudoviruses to infect lung, colon, and kidney cells in the lab.

They, too, found that cells infected with the Delta variant formed more and larger syncytia compared with cells infected with the wild type strain of the virus. The authors write that their findings suggest Delta could “cause more tissue damage, and thus be more pathogenic, than previous variants.”Researchers say it’s important to remember that, while interesting, this research isn’t conclusive. Hamsters and cells aren’t humans. More studies are needed to prove these theories.

Scientists say that what we already know about Delta makes vaccination more important than ever.

“The net effect is really that, you know, this is worrisome in people who are unvaccinated and then people who have breakthrough infections, but it’s not…a reason to panic or to throw up our hands and say you know, this pandemic is never going to end,” Dr. Tuite said, “[b]ecause what we do see is that the vaccines continue to be highly protective.”

A version of this article first appeared on


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