Final answer:
Flushing and dizziness are considered an adverse effect of omalizumab. Pain at the injection site is common but not adverse, and the respiratory rate mentioned is normal. A peak flow reading of 75% may indicate asthma control issues but is not directly related to omalizumab adverse effects.
Step-by-step explanation:
Among the listed options for a client who has received omalizumab, the finding that would be considered an adverse effect is flushing and dizziness. Pain at the injection site is a common side effect but not typically considered an adverse effect. A respiratory rate of 22 breaths/min is within the normal range. A peak flow reading of 75% of normal could be a concern if it represents a significant drop for the individual, but does not directly indicate an adverse reaction to omalizumab; instead, it could be a sign of suboptimal asthma control or progression of the illness.