One important question is whether the Delta strain will make you sicker than the original virus. “Based on hospitalizations tracked in Great Britain [which has been about a month ahead of the U.S. with Delta], the variant is probably a bit more pathogenetic,” Dr. Wilson says. While more research is needed, early information about the severity of Delta includes a study from Scotland that showed the Delta variant was about twice as likely as Alpha to result in hospitalization in unvaccinated individuals (and vaccines reduced that risk significantly).
Another question focuses on how Delta affects the body. There have been reports of symptoms that are different than those associated with the original coronavirus strain, Dr Yildirim says. “It seems like cough and loss of smell are less common. And headache, sore throat, runny nose, and fever are present based on the most recent surveys in the U.K., where more than 90% of the cases are due to the Delta strain,” she says.
It’s unclear whether Delta could cause more breakthrough cases—infections in people who have been vaccinated or have natural immunity from a prior COVID-19 infection, which so far have been rare in general. “Breakthrough is a big question,” Dr. Wilson says. “At least with immunity from the mRNA vaccines, it doesn’t look like it will be a problem.” A Public Health England analysis (in a preprint that has not yet been peer-reviewed) showed that at least two of the vaccines are effective against Delta. The Pfizer-BioNTech vaccine was 88% effective against symptomatic disease and 96% effective against hospitalization from Delta in the studies, while Oxford-AstraZeneca (which is not an mRNA vaccine) was 60% effective against symptomatic disease and 93% effective against hospitalization. The studies tracked participants who were fully vaccinated with both recommended doses.
Moderna has also reported on studies (not yet peer-reviewed) that showed its vaccine to be effective against Delta and several other mutations (researchers noted only a ”modest reduction in neutralizing titers” against Delta when compared to its effectiveness against the original virus). Johnson & Johnson also has reported that its vaccine is effective against the Delta variant, showing only a small drop in potency compared with its effectiveness against the original strain of the virus.
“So, your risk is significantly lower than someone who has not been vaccinated and you are safer than you were before you got your vaccines,” Dr. Yildirim says.
Will vaccinated people need booster shots to protect against Delta? Once again, it’s too soon to know whether we will need a booster modified to target the Delta variant—or any other variant. (Nor do experts know with certainty yet if vaccinated people will need an additional shot at some point to boost the overall immunity they got from their first shots.)
There are additional questions and concerns about Delta, including Delta Plus—a subvariant of Delta, that has been found in the U.S., the U.K., and other countries. “Delta Plus has one additional mutation to what the Delta variant has,” says Dr. Yildirim. This mutation, called K417N, affects the spike protein that the virus needs to infect cells, and that is the main target for the mRNA and other vaccines, she says.
“Delta Plus has been reported first in India, but the type of mutation was reported in variants such as Beta that emerged earlier. More data is needed to determine the actual rate of spread and impact of this new variant on disease burden and outcome,” Dr. Yildirim adds.
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