Two new large studies, one based on outcomes among US children and teens and the other on adults in Japan, show COVID-19 vaccines are protective against long COVID. Both studies were conducted when the Omicron strain of the virus was dominant, with the first also assessing the Delta variant.
In the first study, published in eClinicalMedicine, researchers measured the real-world efficacy of the Pfizer (BNT162b2) vaccine against long COVID in children and adolescents using data from 20 US health systems collected in as part of the RECOVER PCORnet electronic health record (EHR) Program.
Three cohorts were constructed: (1) adolescents 12 to 20 years old during the Delta phase (July 1 to November 30, 2021), (2) children 5 to 11 years and (3) adolescents 12 to 20 during the Omicron phase (January 1 to November 30, 2022). Outcomes were compared among those who received a first dose of the Pfizer vaccine to those with no receipt of COVID-19 vaccines.
In total, 112,590 adolescents (88,811 vaccinated) were included in the cohort for the analysis against the Delta variant, and 188,894 children (101,277 vaccinated), and 84,735 adolescents (37,724 vaccinated) were included for the analysis against the Omicron variant.
Preventing long COVID by averting infections
For adolescents during the Delta period, the estimated effectiveness of the BNT162b2 vaccine against long COVID was 95.4% (95% confidence interval [CI], 90.9% to 97.7%). During Omicron, the estimated effectiveness against long COVID among children was 60.2% (95% CI, 40.3% to 73.5%), and it was 75.1% (95% CI, 50.4% to 87.5%) among adolescents.
The risk reduction in developing long COVID was largely linked to reducing the risk of COVID infection in the first place.
The effects through protecting againt SARS-CoV-2 infections were estimated as 0.04 (95% CI, 0.03 to 0.05) among adolescents during Delta phase, and 0.31 (95% CI, 0.23 to 0.42) among children and 0.21 (95% CI, 0.16 to 0.27) among adolescents during the Omicron period.
The higher effectiveness of the BNT162b2 vaccine during the Delta phase, relative to the Omicron period, can be attributed both to its protection against Delta infections and to the fact that the primary benefit of the vaccine on long COVID stems from its capacity to prevent infection.
"The higher effectiveness of the BNT162b2 vaccine during the Delta phase, relative to the Omicron period, can be attributed both to its protection against Delta infections and to the fact that the primary benefit of the vaccine on long COVID stems from its capacity to prevent infections," the authors concluded. "With the genetic evolution of Omicron strains that generally are more highly transmissible with much lower severity of symptoms, infection rates are higher and vaccine effectiveness has been lower."
Three or more doses tied to less long COVID in women
In the second study, a population-based analysis from Japan, researchers found the vaccine effectiveness of three or more doses of COVID vaccine against Omicron-related long COVID to be 30%, and against neurologic symptoms of long COVID it was 39%.
The protection, however, was found only in women. The study was published yesterday in Clinical Microbiology and Infection.
A total of 7,936 participants aged 20 to 69 years, who were infected from July 1 to August 31, 2022, were included in the study. Of those, 940 (11.8%) had at least one post-COVID, or long-COVID, symptom, according to a self-administered questionnaire.
Participants who had three or more COVID-19 vaccine doses had a 30% lower probability of long-COVID symptoms, with the odds ratio (OR) of 0.70 (95% CI, 0.53 to 0.90), although there was no association with one or two doses.
Furthermore, the risk reduction was seen in women with three or more COVID vaccine doses but not in men.
There was no significant association for respiratory symptoms, but those with three or more COVID vaccine doses reported fewer neurologic symptoms compared to unvaccinated participants (OR, 0.61; 95% CI, 0.45 to 0.83).