The World Health Organization (WHO) authorized an eighth Covid-19 vaccine for emergency use, a CDC report suggests immunity from vaccination is more consistent than natural immunity, and more in this week's roundup of Covid-19 news.

• Health regulators in the United Kingdom on Thursday authorized molnupiravir, Merck's antiviral Covid-19 pill, becoming the first country to clear the drug for use in patients, the Wall Street Journal reports. "The first global authorization of molnupiravir is a major achievement in Merck's singular legacy of bringing forward breakthrough medicines and vaccines to address the world's greatest health challenges," said Merck CEO Robert Davis. "We will continue to move with both rigor and urgency to bring molnupiravir to patients around the world as quickly as possible." Last month, Merck applied to FDA for emergency use authorization of its antiviral drug, and the agency's expert advisory committee is scheduled to review the drug on Nov. 30. According to the Journal, the U.S. could authorize Merck's drug by the end of the year, depending on the advisory committee's decision. (Hopkins, Wall Street Journal, 11/4; Knutson, Axios, 11/4)

• According to data from Johns Hopkins University (JHU), the total number of Covid-19 deaths worldwide has now surpassed five million. The countries with the highest number of Covid-19 deaths are the United States (745,800+), Brazil (607,000+), and India (450,000+). However, Amber D'Souza, a professor of epidemiology at JHU's Bloomberg School of Public Health, said the true number of Covid-19 deaths may be higher than what the data shows since it only accounts for confirmed cases. "It's quite possible that the number of deaths is double what we see," D'Souza said. "But five million is such a staggering number on its own. No country has been able to escape it." (Reyes, Axios, 11/1; Diaz, NPR, 11/1)

• WHO on Wednesday authorized India's Covaxin Covid-19 vaccine for emergency use—a move that will bolster the global vaccine supply, particularly in low-income nations, The Hill reports. The vaccine, which was developed by Bharat Biotech, is a two-dose regimen taken four weeks apart and is 78% effective against the coronavirus. According to WHO, the Covaxin vaccine is "extremely suitable" for lower- and middle-income countries due to its easy storage requirements compared with other vaccines. "This emergency use listing expands the availability of vaccines, the most effective medical tools we have to end the pandemic," said Mariângela Simão, WHO's assistant director-general for access to medicines and health products. Currently, WHO has authorized eight Covid-19 vaccines for emergency use, The Hill reports. (Falconer, Axios, 11/4; Vakil, The Hill, 11/3)

• A CDC science brief published last week found that both natural immunity from coronavirus infection and immunity from vaccination are durable for at least six months, but vaccination offers more consistent protection and higher antibody response, the Washington Post reports. For the brief, researchers analyzed data from more than 90 peer-reviewed and preprint studies, as well as unpublished CDC data, to compare natural immunity and immunity from vaccination against Covid-19. According to the researchers, both people who are fully vaccinated and those who have had a previous Covid-19 infection have "a low risk of subsequent infection for at least six months." However, the researchers said vaccination provides "higher, more robust, and more consistent level of immunity to protect people from Covid-19 than infection alone." Overall, CDC recommends that everyone, regardless of prior infection, be vaccinated against Covid-19 since it is unclear how long natural immunity lasts, The Hill reports. (Sun/Achenbach, Washington Post, 11/1; Williams, The Hill, 11/2)

• A real-world study of the Johnson & Johnson (J&J) Covid-19 vaccine found that it was 73.6% effective against infection from the coronavirus, CNN reports. For the study, researchers analyzed the EHRs of more than 97,500 patients enrolled in the Mayo Clinic Health System across five states from Feb. 27 to July 22. Of the patients, 8,889 were vaccinated with J&J's vaccine, and 88,898 were unvaccinated. Overall, the researchers found that 0.7% of vaccinated patients tested positive for Covid-19 compared with 2.5% of unvaccinated patients, resulting in a vaccine effectiveness of 73.6%. In an accompanying editorial, Zahra Rikhtegaran Tehrani and Mohammad Sajadi, both from the University of Maryland School of Medicine, said the findings suggest there is "room for improvement" for J&J's vaccine. In particular, they noted that J&J's vaccine effectiveness may be improved through an additional dose of either J&J's vaccine or an mRNA vaccine. (Bonifield, CNN, 11/2; Hamza, MedPage Today, 11/3)

• A study published in The Joint Commission Journal on Quality and Patient Safety found that over 13% of patients hospitalized with Covid-19 visited EDs or were readmitted after 30 days, Becker's Hospital Review reports. For the study, researched examined 576 adult Covid-19 patients admitted to an academic medical center between March 21 and June 29, 2020 and identified patients who had been readmitted after discharge. Of the patients, 13.2% had an unplanned hospital revisit within 30 days of being discharge, with 3.6% visiting an ED without being admitted and 9.5% being readmitted to the hospital. The most common diagnoses at the revisits were worsening Covid-19 (11.8%), bacterial pneumonia (7.9%), and urinary tract infection (6.6%). The top contributing factors to readmissions were patient or caregiver misunderstanding of discharge medication, inappropriate choice of discharge location, inadequate treatment of medical conditions, discharge without a needed procedure, and premature discharge. According to the authors, more than a quarter of these revisits were potentially preventable. (Gleeson, Becker's Hospital Review, 10/29; The Joint Commission, 10/28)