Feeling unwell after your Covid shot? So it probably works.

Fever, chills and fatigue may all be signs of vigorous antibody production, according to a new study.

< p class="css-at9mc1 evys1bk0 ">New study has an encouraging message for Americans who avoid Covid vaccines because of concerns about side effects: chills, fatigue, headaches and malaise that may follow vaccination may be signs of a vigorous immune response.

< p class="css-at9mc1 evys1bk0">People who had these side effects after the second dose of a Covid vaccine had more of antibodies against the coronavirus one month and six months after the injection, compared to those who had no symptoms, according to the new study. Increased skin temperature and heart rate also signal higher antibody levels.

"We know that vaccine uptake can be difficult, and in some cases that may be the case because some people have strong reactions to the vaccine,” said Aric Prather, a clinical psychologist at the University of California, San Francisco, who led the study.

“I hope this actually helps alleviate some of those concerns,” said Dr. Prather, who studies how behavioral factors affect the immune system. “Actually , these symptoms, while they may be unpleasant, may actually work for you."

The study was posted online last week. was not reviewed for publication in a scientific journal. But several experts said it was well done and its results were consistent with other research.

The relative increase in antibody levels in those who experienced side effects was small and does not mean that people without symptoms do not mount a strong immune response, experts said.

“The absence of side effects should not be taken as a sign that the vaccine is effective. doesn’t work,” said Alessandro Sette, co-director of the Center for Vaccine Innovation at the La Jolla Institute of Immunology, who was not involved in the work.

An earlier study found that 98% of people who experienced no adverse effects still produced large amounts of antibodies, compared to 99% of those who had localized symptoms or worse, said the Dr. Sette.

Nevertheless, the new results suggest that people who have a difficult time after vaccination are likely to be well protected against the virus. “If you're feeling bad, there's a good chance you'll mount a pretty reasonable immune response,” said Deepta Bhattacharya, an immunologist at the University of Arizona who was not involved in the new study.

In research published last year, Dr. Bhattacharya and colleagues examined the vaccine responses of 2,354 people, about half of whom took a painkiller to relieve the effects side effects of the injection.

In mice, nonsteroidal anti-inflammatory drugs, such as aspirin and ibuprofen, seriously impair immune responses to the coronavirus. But Dr Bhattacharya's team found that in humans, the drugs did not inhibit the immune response to Covid vaccines.

Not only that, but those who took painkiller appeared to have more antibodies than those who tolerated the symptoms without medication. The most likely explanation is not that painkillers increase antibody levels, Dr. Bhattacharya said.

"It...