I had a reaction to the first shot, headache, general malaise, etc. for 24 hours. A milder reaction to the second, feeling generally "off" with a borderline migraine for 12-24 hours. With the booster (all shots Moderna FWIW), I didn't have any reaction at all except site tenderness. I'll let Chuck weigh in, but the literature is still saying that while the current boosters are not as effective on Omicron as they were/are on the earlier variants, they are still more effective than your average flu shot (more than 65 percent, I think) so still worth having to a) reduce the chances of illness and b) reduce the severity of illness if caught.