But the vaccine has been known to cause occasional outbreaks, presumably because the procedure used to kill the virus is imperfect. (sciencemag.org)
The embrace of openness has survived, in spite of occasional outbreaks of anti-immigrant sentiment, for the intervening two and a half centuries. (fortune.com)
Virology is being constantly challenged with occasional outbreaks of hazardous viral infections, occurrence of newly emerging viruses and persistent infections. (2018.febscongress.org)