Each person who contracted the coronavirus early in the pandemic likely transmitted it to four or five others, a new study has found. This is double the number originally estimated by the World Health Organization.

Researchers from Duke University, Durham, NC, also found that governments in the 57 countries they analyzed had about 20 days from their first reported cases to enforce measures that would prevent transmission, reported the Miami Herald. The time available to reduce infections and prevent outbreaks was much smaller than expected, investigators said.

Many of the countries studied were slow to ramp up prevention measures. The researchers calculated that any actions enforced 44 days or more after the first cases were discovered were “virtually ineffective at preventing coronavirus outbreaks,” according to the news outlet.

To reach a level of herd immunity that would keep COVID-19 from becoming an epidemic again, fully 78% of the world’s population would need to be infected with the coronavirus, the researchers said. 

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Spread of COVID-19 driven by few individuals; children a key  A study of more than a half-million people in India exposed to SARS-CoV-2 reveals that the virus’ continued spread is driven by a small percentage of those who become infected. Children and young adults were found to be potentially much more important to transmitting the virus — especially within households — than previous studies have identified, according to researchers from the United States and India. Full findings were published in the journal Science.