| In this week's edition of the Covid Q&A, we look at the risk of infection with the delta variant. In hopes of making this very confusing time just a little less so, each week Bloomberg Prognosis is picking one question sent in by readers and putting it to experts in the field. This week's question comes to us from Gary. Gary wonders if the delta variant presents a greater risk of infection than other variants if you've already had Covid and are unvaccinated. He asks: Is the delta variant more likely to cause reinfection than other variants? How serious are the reinfections? First off, let's get one big thing out of the way. Regardless of whatever variants are circulating, it's important to get vaccinated even if you have already had Covid-19. We simply don't understand how long protective immunity lasts after getting Covid. It's likely that it varies from person to person. Studies have suggested vaccines provide a significant boost in immunity to people who have already had the virus — and a surer bet of protection against delta and whatever other variant comes along. While we don't yet know how long protective immunity from vaccines last, it's clear that immunity lasts for at least six months and potentially far longer.
Now, to the question at hand. For advice here we turn to Andrew Noymer, a professor of public health at University of California, Irvine. Researchers are investigating how likely people are to get Covid-19 a second time. At present, we know that reinfection can happen, as can so-called breakthrough infections in people who are fully vaccinated. More research on delta is needed, but a new study Thursday suggested the variant is able to evade natural antibodies made in our bodies after infection. Looking at blood drawn from 162 patients, scientists found that while antibodies from people infected with Sars-CoV-2 didn't neutralize delta very well, after just one vaccine dose, antibodies from people with a previous infection were able to neutralize all four strains of the virus tested. Antibodies from people who had only one dose of a vaccine and hadn't previously been infected with the virus didn't fare as well. Antibodies from people who were fully vaccinated but hadn't had Covid performed well, confirming other evidence that the vaccines are extremely effective against delta. The early evidence suggests that if you're unvaccinated—whether you've had Covid or not—you are more vulnerable to delta infection. Once again: vaccination for the win.
Noymer says the real significance of delta isn't that it makes people sicker, but that it spreads so quickly — creating more opportunities for infection, and more opportunities for new variants to form that may be better at evading vaccines.
"I'm worried about delta, but I am not just worried about delta," Noymer says. Other variants, he says, are "waiting in the wings." There are more than enough unvaccinated people in the U.S. to start a new wave of Covid infections, according to Noymer.
"There may be a variant that comes around the corner where the vaccines don't work," he says. Thanks to all of you for writing in this week! Next Sunday, we'll be answering the best question we receive again. So if you have any, we want to hear from you. Write to us at CovidQs@bloomberg.net—Kristen V. Brown | 
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