Chills, soreness after COVID vaccine mean better protection, UConn study finds

A new UConn study finds that COVID-19 vaccines provided better protection in people who experienced side effects. In addition, those who had COVID-19 before vaccines were available had better and more durable COVID-neutralizing antibodies. The study tracked roughly 300 healthcare workers for about a year beginning just after vaccines became available in 2021. The healthcare workers were vaccinated and reported symptoms and prior infections. Researchers collected blood from the workers and checked the levels of protective antibodies. "We had a population that was more or less continually exposed to COVID through work," said Dr. Kevin Dieckhaus, author of the study and chief of the Division of Infectious Diseases at UConn Health in Farmington. Dieckhaus said that at that time nobody knew how durable the vaccine would be, so they put out a call for healthcare workers to answer surveys and donate blood over time. The study, published in February, found that by month nine, all the workers had reduced levels of COVID-19 antibodies. But workers who had muscle aches, headaches or chills were more likely to have had sustained antibody responses that decayed more slowly than people who did not experience side effects. People who had both a prior COVID infection and vaccine side effects, like fever and fatigue, were 30-50 percent more likely to have sustained antibody responses with gentle declines. No workers experienced an allergic reaction to a vaccine. The side effects were all the standard “gross feelings” associated with vaccination. Workers who experienced no side effects and no prior infection had far sharper declines in antibody production by the ninth month of the study. "Having some redness and swelling around the injection site, having fatigue, chills, muscle pains and so on," Dieckhaus said, "these are the ones that really stood out. If you had these symptoms, the more likely you were to be someone who was going to have a longer duration of antibodies." When you’re sick, many symptoms you experience come from the immune system mobilizing to fight the infection. Fever, chills, and soreness are side effects of immune chemical signaling, anti-microbial activity, and the recruitment of immune cells to the site of infection. The immune system treats a vaccination like an infection even though it isn’t one. Vaccines carry a danger signal called an adjuvant that tricks the immune system into seeing the vaccine as an attack rather than some stray protein or RNA to digest. RNA outside a cell is a danger signal because RNA should only be seen inside cells under normal circumstances. "This is spot-on what we would have predicted as immunologists," said Dr. Derya Unutmaz, an immunology professor at The Jackson Laboratory. He explained that the symptoms people experienced after vaccination could be taken as evidence of the immune system working. "It's nice to know that if you had some adverse effects, that's because your response is somewhat better." In other words, the COVID vaccines simulate an infection, summon the immune system, and trigger some of the physical sensations of fighting off an infection. The study also demonstrated the immune system’s capacity to improve its reaction to a specific infection over time. People in the study with prior COVID infections experienced better long-term immunity than those who hadn’t because of immune memory. If the immune system sees the same disease again, it pounces faster and harder. Vaccines are treated like infections by the immune system, so they’re a way to establish memory without getting truly sick. The study saw this effect in the rare breakthrough infections among the healthcare workers. Within days of a breakthrough infection, the antibody levels of the vaccinated workers skyrocketed. Typically, the immune system takes about a week to mount an antibody response to a new infection. "When you get a vaccine, it's like calling the immune system back from the front lines for training," said Unutmaz. "It's not like your immune system is perfect after one infection." In the future, the study group hopes to trace the way this plays with different variants and boosters. The healthcare workers are still contributing blood to the study. Many have gotten boosters. "We're continuing to collect the data," Dieckhaus said. "The reason we stopped at month nine in this study is that's when boosters became available. So we'll be adding boosters to the next study."

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