The risk of lingering symptoms after COVID-19 appears influenced by the strain of coronavirus that caused the infection, according to an analysis from the U.K., where an estimated 1.8 million people reported experiencing long COVID in early April.

The odds of reporting fatigue, shortness of breath, difficulty concentrating and other persistent symptoms were 50% lower following infections likely caused by the omicron BA.1 variant than those likely caused by the delta strain, the Office for National Statistics said in a report Friday. The difference was found only among adults who were double vaccinated when infected. Among those who were triple vaccinated, the difference wasn’t statistically significant.

Among triple vaccinated adults, the odds of reporting long COVID were higher following infection with the omicron BA.2 variant than the BA.1 variant, the analysis found.

More than two-thirds of those with self-reported long COVID, or 1.2 million people, said their symptoms adversely affected their day-to-day activities, and almost a fifth said their symptoms limited them a lot, according to the statistics bureau.

Most long COVID symptoms don’t seem to be life-threatening, but things like shortness of breath or fatigue can be disabling. The U.S. Government Accountability Office said in a March report that long COVID could affect the broader economy through decreased labor participation and an increased need for use of Social Security disability insurance or other publicly subsidized insurance.