The lymphocyte index on the blood routine after viral infection is usually increased, but there may also be a decrease, and there may also be an increase in neutrophils.
When the organism is infected by a virus, it tends to lead to the proliferation of lymphocytes, i.e., the routine blood tests show lymphocytes higher than the normal range (0.8~4) x 10^9/L, for example, this is the case with both EBV and cytomegalovirus infections.
However, certain viral infections can also lead to a decrease in lymphocytes, such as novel coronaviruses. Some viral infections result in an increase in neutrophils with no change in lymphocytes, such as hemorrhagic fever caused by hantavirus.
Patients are advised to seek professional advice with the results of routine blood tests to avoid delays.