Is candidiasis a common secondary infection of viral pneumonia?

Less than. Staph infections are much more common than candida following a viral pneumonia, but certainly they can occur. Generally, overgrowth of candida that is local (thrush or vaginosis) can occur in any patient. Systemic candidiasis or candidal pneumonia is seen, but usually only in the immune compromised or severely ill patient.
No . Pulmonary candidiasis causing pneumonia is rare and usually only seen in those who are severely immuno-suppressed.

Related Questions

Is candidiasis a common secondary infection of bacterial pneumonia?

Yes. Oral candidiasis (thrush), or vaginosis is commonly seen in people treated with antibiotics. Both usually resolve with local treatment. Systemic candidiasis does occur in patients recovering from severe sepsis, but is not "common" outside the ICU except in the immune compromised. Read more...