What motivated the powers of europe to cover up the spanish flu's existence

When the flu broke out in 1918, wartime press censorship was more entrenched in European countries because Europe had been fighting since 1914, while the United States had only entered the war in 1917. It's hard to know the scope of this censorship, since the most effective way to cover something up is to not leave publicly-accessible records of its suppression. Discovering the impact of censorship is also complicated by the fact that when governments pass censorship laws, people often censor themselves out of fear of breaking the law.