Pfizer's COVID-19 antiviral Paxlovid cut the prevalence of hospitalizations and deaths in half when it was used within the first day of diagnosis, according to a study published Dec. 16 in Nature.
To find out whether initiating the drug immediately after symptom onset would improve outcomes, researchers analyzed medical data from more than 80,000 patients in Hong Kong who used Paxlovid between March 2022 and January 2023.
By using Paxlovid between zero to one days after COVID-19 symptom onset, the rate of all-cause deaths and hospitalizations were half the rate of those recorded among delayed users, or those who took Paxlovid after two days.
The risk grew as more days passed since symptoms appeared, the researchers found. The incidence of 28-day all-cause deaths and hospitalizations was 5.1% for early initiators and 6.6% for delayed users.
A caveat was a risk of COVID-19 rebound that was higher among early users of Paxlovid, but this was "based on limited sample sizes and thus subject to high uncertainty," the authors wrote.