Stability of an aluminum salt-adjuvanted protein D-conjugated pneumococcal vaccine after exposure to subzero temperatures

Accidental exposure of a vaccine containing an aluminum-salt adjuvant to temperatures below 0 degrees C in the cold chain can lead to freeze damage. Our study evaluated the potential for freeze damage in a licensed aluminum-salt-containing protein-D-conjugated pneumococcal vaccine (PHiD-CV; Synflorix, GSK) in conditions that included static storage, single subzero-temperature excursions, and simulated air-freight transportation. Several parameters were assessed including freezing at subzero temperatures, aluminum-salt-particle size, antigen integrity and immunogenicity in the mouse. The suitability of the WHO's shake test for identifying freeze-damaged vaccines was also assessed. During subzero-temperature excursions, the mean temperatures at which PHiD-CV froze (-16.7 degrees C to -18.1 degrees C) appeared unaffected by the type of vaccine container (two-dose or four-dose vial, or single-dose syringe), vaccine batch, rotational agitation, or the rate of temperature decline (-0.5 to -10 degrees C/hour). At constant subzero temperature and in simulated air-freight transportation, the freezing of PHiD-CV appeared to be promoted by vibration. At -5 degrees C, no PHiD-CV sample froze in static storage (>1month), whereas when subjected to vibration, a minority of samples froze (7/21, 33%) within 18hours. At -8 degrees C with vibration, nearly all (5/6, 83%) samples froze. In these vibration regimes, the shake test identified most samples that froze (10/12, 93%) except two in the -5 degrees C regime. Nevertheless, PHiD-CV-antigen integrity appeared unaffected by freezing up to -20 degrees C or by vibration. And although aluminum-salt-particle size was increased only by freezing at -20 degrees C, PHiD-CV immunogenicity appeared only marginally affected by freezing at -20 degrees C. Therefore, our study supports the use of the shake test to exclude freeze-damaged PHiD-CV in the field.