The 5 Most Common Signs You Caught Delta If You're Vaccinated, Study Says

The latest research also found that those who are older are particularly at risk.

The Delta variant has proven to be one of the most difficult hurdles faced during the COVID-19 pandemic. The highly contagious strain has spread quickly among the unvaccinated and has also shown that it can still infect some people who've received both of their shots. Now, a new study published in the journal The Lancet Infectious Diseases has shed some new light on the variant, including certain common symptoms for vaccinated people to be aware of that could be signs you've actually caught Delta.

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The very large study analyzed data collected using the Zoe COVID Study app between Dec. 8 and July 4, which included 1,240,009 users who had received at least one dose of vaccine and 971,504 who reported being fully vaccinated. Researchers found that while "vaccination was associated with lower symptom reporting for almost all symptoms across all age groups," a small percentage of fully vaccinated respondents reported symptomatic infection. Out of the 906 patients included in that group, 39 percent reported sneezing as a symptom, 41.6 percent reported headache, 43 percent had a runny nose, 43.7 percent experienced fatigue, and 61.9 percent listed running a fever.

Despite the small segment of respondents showing signs of illness, the study added to mounting evidence that vaccines are highly effective against breakthrough illness. Only 0.5 percent of partially vaccinated and 0.2 percent of fully vaccinated patients in the study tested positive for COVID, also finding that breakthrough infections were twice as likely to be asymptomatic in those who were fully vaccinated. In addition, those who had received both shots were also half as likely to develop lingering symptoms known as long COVID after such infections.

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Researchers also found a connection between certain age groups and the likelihood of breakthrough infections. Results showed that frail seniors aged 60 and older were about twice as likely to contract the virus after having one dose compared to healthy adults. According to Claire Steves, MD, the study's lead researcher, such findings justify the call for additional shots to be administered in certain vulnerable parts of the population.

"In terms of the burden of long COVID, it's good news that our research has found that having a double vaccination significantly reduces the risk of both catching the virus and, if you do, developing long-standing symptoms," she said in a statement. "However, among our frail, older adults and those living in deprived areas, the risk is still significant, and they should be urgently prioritized for second and booster vaccinations."

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The study's authors noted some limitations with the study, including the long data period that saw an overlap in time between when the Alpha variant was overtaken by the Delta variant as the dominant strain in the U.K. All cases are also self-reported to the app, meaning that certain metrics on symptoms could be inaccurate. But they also noted the major implications their findings could have on emphasizing the importance of getting fully vaccinated.

"Vaccinations are massively reducing the chances of people getting long COVID in two ways," Tim Spector, MB, a professor of genetics from King's College London and lead investigator of the ZOE COVID Study, said in a statement. "Firstly, by reducing the risk of any symptoms by eight to 10 fold and then by halving the chances of any infection turning into long COVID, if it does happen. Whatever the duration of symptoms, we are seeing that infections after two vaccinations are also much milder, so vaccines are really changing the disease and for the better. We are encouraging people to get their second jab as soon as they can."

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Zachary Mack
Zach is a freelance writer specializing in beer, wine, food, spirits, and travel. He is based in Manhattan. Read more
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