When CCP did a controlled eradication of pest animals destroying their crops, it caused the great Chinese famine and millions died. Mostly because these pest animals were natural enemies to even worse pests.
Although the sparrow campaign ended in disaster, the other three anti-pest campaigns may have contributed to the improvement in the health statistics in the 1950s.[18]
Seems the birds may have been the only screw up. No harm reported from the mosquitos, flies, and rats.