Adjuvants, pharmacological or immunological agents that increase the immune system's response to the antigen in a vaccine,
are becoming more common in vaccine formulations. Oil-in-water emulsions and liposome adjuvants in particular are being pursued
by vaccine manufacturers as a cost effective way to meet worldwide vaccine demand. More robust filtration solutions are needed
to achieve sterile filtration of these streams, since they can be difficult to validate for desired capacity and retention
under desired process conditions. A team of researchers conducted an investigation of the variables that affect capacity and
bacterial retention during filtration of a model emulsion adjuvant. Based on the results, we developed and manipulated the
model stream to determine how to optimize the process for improved performance. The study found that processing conditions,
filter selection, and feed stream properties all affect filtration performance. Temperature, pressure, membrane selection,
and particle size and loading can be manipulated to improve process efficiency and ensure product sterility.
Adjuvants increase the response of the immune system to the antigen in the vaccine, improving its efficacy and enabling reduced
dosage to achieve the desired immune response. In use since the 1930s, the oldest adjuvant is alum (aluminum salts), which
is still used in the industry today. Since aluminum salts are >0.2 μm, they cannot be sterilized by 0.2 μm filtration, so
typically they are heat sterilized instead.
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Newer adjuvants, including oil-in-water emulsions and liposomes, were introduced to the market more than a decade ago. These
novel adjuvant formulations are more universal than alum and are thought to minimize adverse patient reactions. They are approved
for use in vaccine formulations in Europe, Asia, Canada, and Mexico. The benefits of these novel adjuvants are driving their
increased use for the foreseeable future.1,2 This increased use has brought more attention to the validation and filtration challenges associated with each. Millipore
undertook a study to better understand the mechanisms that affect capacity and bacteria retention in the presence of emulsions
and liposomes, and use this understanding to develop robust filtration solutions.