Comparing reactogenicity of COVID-19 vaccine boosters: a systematic review and meta-analysis.

INTRODUCTION: Different COVID-19 vaccines are being utilized as boosters. This systematic review and meta-analysis aims to evaluate the reactogenicity of COVID-19 vaccines given as booster doses, according to vaccine type, dose, timing, participant characteristics and primary immunization regimen received. METHODS: Four databases (MEDLINE, Embase, Web of Science and CENTRAL) were searched for randomized controlled trials between 1 January 2020 and 1 January 2023 according to predetermined criteria. RESULTS: Twenty-eight studies describing 19 vaccines of four different types (viral vector, inactivated, mRNA and protein sub-unit) were identified. BNT162b2 vaccine (Pfizer-BioNTech) was selected as the control as it was most often compared with other vaccines. Fever, fatigue, headache, injection-site pain, redness, and swelling were the most frequently reported solicited events. mRNA vaccines were the most reactogenic, followed by viral vector vaccines and protein sub-unit vaccines, while inactivated vaccines were the least reactogenic. Full-dose vaccines were more reactogenic than half-dose vaccines. Heterologous BNT162b2 boosters were more reactogenic than boosters with the same vaccine used for primary immunization. CONCLUSIONS: COVID-19 vaccine booster schedules have distinct reactogenicity profiles, dependent on dose and vaccine type, which may allow targeted recommendations and provide choice for specific populations. Greater standardization of adverse event reporting will aid future studies.

Brown adipose tissue and seasonal variation in humans.

OBJECTIVE: Brown adipose tissue (BAT) is present in adult humans where it may be important in the prevention of obesity, although the main factors regulating its abundance are not well established. BAT demonstrates seasonal variation relating to ambient temperature and photoperiod in mammals. The objective of our study was therefore to determine whether seasonal variation in BAT activity in humans was more closely related to the prevailing photoperiod or temperature. RESEARCH DESIGN AND METHODS: We studied 3,614 consecutive patients who underwent positron emission tomography followed by computed tomography scans. The presence and location of BAT depots were documented and correlated with monthly changes in photoperiod and ambient temperature. RESULTS: BAT activity was demonstrated in 167 (4.6%) scans. BAT was demonstrated in 52/724 scans (7.2%) in winter compared with 27/1,067 (2.5%) in summer months (P < 0.00001, chi(2) test). Monthly changes in the occurrence of BAT were more closely related to differences in photoperiod (r(2) = 0.876) rather than ambient temperature (r(2) = 0.696). Individuals with serial scans also demonstrated strong seasonal variation in BAT activity (average standardized uptake value [SUV(max)] 1.5 in July and 9.4 in January). BAT was also more common in female patients (female: n = 107, 7.2%; male: n = 60, 2.8%; P < 0.00001, chi(2) test). CONCLUSIONS: Our study demonstrates a very strong seasonal variation in the presence of BAT. This effect is more closely associated with photoperiod than ambient temperature, suggesting a previously undescribed mechanism for mediating BAT function in humans that could now potentially be recruited for the prevention or reversal of obesity.