The first known meta-analysis of how SARS-CoV-2 variant type and time since infection influence long-COVID symptoms ties Omicron to brain fog and paresthesia (numbness and tingling), while earlier variants were more likely to cause shortness of breath and loss of smell.
The study also puts the prevalence of the condition at 29%, though it dropped to 23% once the Omicron strain started to dominate.
Investigators in Manila, the Philippines, led the study, which involved searching six databases from December 2019 to December 2025 for studies of adults diagnosed as having long COVID. To estimate pooled prevalence, the team stratified the data by variants of concern (VoC) and follow-up (less or more than six months). The studies were of cross-sectional, case-control, prospective cohort, and retrospective cohort design, and all but one relied on patient self-report.
Among all variants identified, Alpha, Beta, Gamma, Delta, and Omicron were considered VoC. “These VoC have been manifested with various pathologic phenotypes such as heterogeneous disease severity, resistance to neutralizing antibodies, reinfection rates, and vaccine effectiveness,” the study authors wrote.
The study findings were published this week in the International Journal of Infectious Diseases.
Higher prevalence before Omicron
The average participant age was 46.7 years, 41.2% were men, and the average vaccination coverage was 69.6%. The most prevalent pre-infection chronic conditions were high blood pressure (24.2%), obesity (20.0%), and diabetes (8.7%)
The pooled prevalence of long COVID among 35 studies from 19 countries involving 159,000 total participants was 29.4%, with higher prevalence of long COVID in the pre-Omicron (35.5%) than in the Omicron (22.8%) period. The highest prevalence was during the Beta wave (59.5%), and the lowest was tied to the wild-type virus (18.3%). After excluding data sets with mixed or unspecified VoC, the overall prevalence of long COVID was 28.5%.
The long-COVID pooled prevalence at less than six months after infection (27.3%) was comparable to that at six months or later (29.9%). Impaired sleep (32.5%), headache (19.8%), and rash (6.5%) were more prevalent in the six months after infection than at six months or later. In contrast, malaise (general unwellness; 33.1%) and difficulty swallowing (12.1%) were more common after six months. In 29.9% of cases, symptoms lasted more than six months.
Need for tailored management strategies
During all variant periods, fatigue was the most common long-COVID symptom, followed by brain fog, shortness of breath, and sleep problems. Pre-Omicron variants were tied to shortness of breath and loss of smell, while Omicron was linked to brain fog and paresthesia. Most symptoms didn’t wane appreciably over six months.
Our findings underscore that post-COVID-19 condition should not be viewed as a uniform syndrome but rather as a dynamic and multifaceted condition shaped by VoC and temporal factors.
Rates of impaired sleep were higher in the early pre-Omicron era but improved over time. In contrast, heart palpitations and eye problems increased in later pre-Omicron periods.
“Our findings underscore that post-COVID-19 condition should not be viewed as a uniform syndrome but rather as a dynamic and multifaceted condition shaped by VoC and temporal factors,” the authors wrote. “The shifting symptomatology profiles suggest that different mechanisms may drive the persistence of post-COVID symptoms across variants and over time.”
Future research should focus on harmonizing study methodologies and definitions to capture the true burden, variability, and trajectory of long COVID, they said.
“Post-COVID condition remains a burden despite vaccination,” the team concluded. “Distinct symptomatology patterns across VoC and timelines highlight the need for tailored management strategies to mitigate long-term global impacts.”
