Structural damages in adsorbed vaccines affected by freezing

Area of Science:

• Vaccinology
• Materials Science

Background:

• Adsorbed vaccines require specific storage conditions to maintain structural integrity.
• Freeze-sensitive vaccines can undergo significant structural alterations when exposed to freezing temperatures.

Purpose of the Study:

• To investigate the structural damages in adsorbed vaccines subjected to freezing.
• To correlate observed structural changes with altered precipitation characteristics.

Main Methods:

• Scanning electron microscopy (SEM) for structural analysis.
• X-ray analysis of elemental composition.
• Precipitation time measurements.
• Exposure of WHO pre-qualified adsorbed freeze-sensitive vaccines to -25°C for 24 hours.

Main Results:

• Freezing induced structural damage in adsorbed vaccines, characterized by smooth or rough surfaced conglomerates.
• X-ray analysis identified the precipitate as primarily aluminum clutters, indicating broken bonds between adsorbent and antigen.
• Frozen vaccines exhibited significantly faster precipitation times (4.5 times faster on average) compared to non-frozen controls.
• SEM revealed a disrupted lattice structure in frozen samples.

Conclusions:

• Freezing disrupts the structural integrity of adsorbed vaccines, leading to antigen-adsorbent bond breakdown and aluminum aggregation.
• The observed structural changes and accelerated precipitation are scientifically foundational for the "shake test" used to detect freeze-damaged vaccines.