The coronavirus's incubation period has shortened with each new variant, FDA authorizes Novavax's Covid-19 vaccines for adolescents ages 12 to 17, and more in this week's roundup of Covid-19 news.

Case study: Recovery clinics for Covid-19 long-haulers

• Between 2 million and 4 million Americans are currently unable to work due to long Covid, according to a report from the Brookings Institution. It is unclear how many people have long Covid, but the report estimated that roughly 16 million Americans ages 18 to 65 currently have the chronic condition. Of this group, roughly 3 million have not been able to work because of their persistent Covid-19 symptoms, including fatigue, neurocognitive issues, and shortness of breath. "Three million full-time-equivalent workers is 1.8% of the entire U.S. civilian labor force," said Katie Bach, a nonresident senior fellow at Brookings. According to the report, this inability to work has resulted around $170 billion a year in lost wages and is likely contributing to the current labor shortage. David Putrino, director of rehabilitation innovation at Mount Sinai Health System, said the report highlights what doctors routinely see at long Covid clinics."Long Covid definitely affects the ability to remain employed, and we're definitely seeing a lot of people being denied short- and long-term disability and workers' compensation despite the fact that they have a diagnosis of long Covid," Putrino said. (Reddy, Wall Street Journal, 8/24)

• The time between exposure to the coronavirus and the development of symptoms has likely shortened with each new variant, according to a study published in JAMA Network Open. For the study, researchers from Peking University and Tsinghua University in Beijing analyzed data from 142 studies that included 8,112 patients to determine whether the incubation period changed with different coronavirus variants. The researchers found that the mean incubation period of the coronavirus was 6.57 days. However, the incubation period shortened as new coronavirus variants emerged. For example, the incubation period was an average of five days for the alpha variant, 4.5 days for the beta variant, 4.4 days for the delta variant, and 3.4 days for the omicron variant. "Incubation period is one of the most important epidemiological parameters of infectious diseases," the researchers said. "Identifying the incubation period of different variants is a key factor in determining the isolation period." CDC currently recommends people who are exposed to the coronavirus quarantine for five days and then wear a mask for an additional five days. (Carbajal, Becker's Hospital Review, 8/23)

• Most people who were infected by the omicron variant did not realize they had been infected, which likely contributed to the rapid spread of the virus during the omicron surge, according to a new study published in JAMA Network Open. For the study, researchers analyzed blood samples from 2,479 adult patients and employees at Cedars-Sinai Medical Center during the omicron surge at the beginning of the year. Of the 210 participants who had been infected by the omicron variant, which was determined by the presence of antibodies in their blood, 56% did not know they had been infected. In addition, only 10% of those who said they were unaware of infection reported having any symptoms. "We hope people will read these findings and think, 'I was just at a gathering where someone tested positive,' or, 'I just started to feel a little under the weather. Maybe I should get a quick test,'" said Susan Cheng, director of the Institute for Research on Healthy Aging at Cedars-Sinai's Smidt Heart Institute and one of the study's authors. (Miranda, NPR, 8/19)

• Around 98% of Covid-19 reinfections are occurring in individuals who were previously infected more than 90 days ago, which suggests than waning immunity rather than new coronavirus variants are the cause of these cases, according to data from Helix, a lab that assists CDC with viral surveillance. Although Peter Chin-Hong, an infectious disease specialist and professor of medicine at the University of California, San Francisco, said the BA.5 omicron subvariant's high transmissibility has thrown the 90-day reinfection standard "completely out the window," data from Helix shows that the average time between infections has increased. In April, the average time between infections was 230 days, but it was 270 days in July. "New data reinforces our earlier conclusion that while reinfections are rising rapidly, ones that occur within 90 days of the original infection are rare," Helix said. (Gleeson, Becker's Hospital Review, 8/16)

• FDA last week authorized Novavax's Covid-19 vaccine for adolescents ages 12 to 17, Axios reports. In July, FDA authorized the vaccine for adults ages 18 and older, making it the fourth Covid-19 vaccine available in the United States. According to Novavax CEO and president Stanley Erck, the new authorization for adolescents "will hopefully help increase vaccination rates, particularly as we prepare for ongoing surges of COVID-19 with the start of fall and the back-to school season." He added that the company hopes its vaccine, which uses more traditional protein technology rather than mRNA technology, "may have a special role in adolescent vaccination based on parents' and caregivers' familiarity with protein-based vaccines used in other disease areas." Currently, Novavax is conducting a clinical trial of a reformulated vaccine targeting the omicron variant as a potential booster. The trial results are expected by September, and doses could be available in the last three months of the year. (Allassan, Axios, 8/21)

• Older Covid-19 patients who were treated with Paxlovid had lower rates of hospitalization and death during the omicron wave than patients who did not receive the treatment, according to a study published in the New England Journal of Medicine. For the study, researchers analyzed data from 109,254 individuals ages 40 and older who were eligible to receive Paxlovid between Jan. 9 and March 31 at Clalit Health Services in Israel. In total, 3,902 patients received Paxlovid during the study period. The mean age of these patients was 60 years, 39% were 65 years or older, and 60% were women. Patients received Paxlovid an average of two days after testing positive for Covid-19, and 97% completed the full five-day course. Overall, the researchers found that patients ages 65 or older who received Paxlovid had a hospitalization rate of 14.7 cases per 100,000 person-days, compared to 58.9 cases per 100,000 person-days for patients who were not treated. In addition, only two deaths occurred in patients ages 65 and older who received Paxlovid, compared to 158 untreated patients. However, younger patients between the ages of 40 and 64 did not see much benefit from Paxlovid. Hospitalization and deaths rates were roughly the same between patients who received Paxlovid and those who did not. "Our results conform to CDC guidelines to treat high-risk patients, prioritizing those above 65," said Ronen Arbel, one of the study's authors. "No evidence of benefit was found in younger adults." However, Arbel also noted that "whether or not to give a patient nirmatrelvir [Paxlovid] is a clinical decision" and "[i]t should not be limited [to those over 65], but rather a factor to consider in the risk assessment of patients based on their risk profile and additional clinical considerations, including symptoms." (Hein, MedPage Today, 8/24)