Yes. Sperm quality varies quite often and is dependent on lifestyle factors. It is likely that stress or the flu affect spermatogenesis, and the results of a semen analysis report appear altered, including problems of oligozoospermia, asthenozoospermia, etc.
The good news is that a man can recover his fertility within 3 months if the cause of infertility is improved or disappears. A balanced diet, doing sports, and quitting toxic habits can contribute to improving sperm quality to a large extent.