Time-domain statistical studies of mid-infrared and submm variability in nearby star-forming regions show that at least half of all protostars are variable. In this study, we present a statistical analysis of the mid-infrared variability of Young Stellar Objects (YSOs) in the distant, massive star-forming region W51, based on data from the Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) All-Sky Survey. From a catalog of 81 protostars, 527 disk objects, and 37,687 other sources, including diskless pre-main sequence stars (Class III) and likely evolved contaminants such as AGB stars (collectively labeled as PMS+E), we identified significant variability in both the 3.4 μm(W1) and 4.6 μm(W2) bands. Due to the large distance (∼5.4 kpc) and high extinction of W51, our sample primarily includes intermediate- to high-mass YSOs (≥2 M⊙), in contrast to nearby star-forming regions such as Taurus or the Gould Belt, which are dominated by low-mass stars (≤1M⊙). This mass bias may affect the observed variability characteristics and their interpretation. Specifically, 11.1% of protostars, 7.6% of Disk objects, and 0.6% of PMS+E sources exhibited secular variability in the W2, while 8.6% of protostars, 2.3% of Disk objects, and 0.5% of PMS+E sources exhibited stochastic variability. Similar trends were observed in the W1 band. Both the fraction and amplitude of variability increase toward earlier evolutionary stages. Protostars exhibit predominantly stochastic variability with high amplitudes, likely driven by dynamic accretion, and extinction changes. In contrast, disk objects show more secular variability, including linear, curved, and periodic patterns, possibly caused by moderate accretion changes or geometric modulation in the inner disk. Analysis of brightness and color changes revealed that protostars typically become redder as they brighten, while disk objects show more complex behavior: they appear roughly balanced in W1 but more often become bluer in W2. These trends are consistent with enhanced dust emission or extinction in protostars, and reduced extinction or accretion-induced hotspot modulation in disk objects. These trends reflect the distinct physical mechanisms at play across evolutionary stages and demonstrate that mid-infrared variability provides useful insight into the accretion and disk evolution processes in young stars.

This work presents four high-amplitude variable YSOs (≃3 mag at near- or mid-IR wavelengths) arising from the SPICY catalog. Three outbursts show a duration that is longer than 1 year, and are still ongoing. And additional YSO brightened over the last two epochs of NEOWISE observations and the duration of the outburst is thus unclear. Analysis of the spectra of the four sources confirms them as new members of the eruptive variable class. We find two YSOs that can be firmly classified as bona fide FUors and one object that falls in the V1647 Ori-like class. Given the uncertainty in the duration of its outburst, an additional YSO can only be classified as a candidate FUor. Continued monitoring and follow-up of these particular sources is important to better understand the accretion process of YSOs.