1. INCUBATION PERIOD According to a study published August 22 in JAMA Network Open, the incubation period of COVID-19 has decreased gradually as SARS-CoV-2 has continuously evolved and mutated, producing variants with different enhanced transmission and virulence. The incubation period is the interval between exposure and development of symptoms and is an important epidemiologic indicator for understanding transmission. Based on the authors’ meta-analysis, the initial “wild type” strain first detected in Wuhan, China, in 2019 had an incubation period of approximately 5.2 days. Later in 2020, the Alpha variant that quickly became dominant in the UK had an incubation period of about 5 days. The Beta variant was identified shortly after and showed a shortened incubation period of 4.5 days, followed by the Delta variant with 4.41 days. The incubation period for Omicron infection is currently 3.42 days. While a decrease in incubation period often is associated with more severe disease, the decrease with COVID-19 means it makes it much more difficult to control transmission, because the faster someone becomes contagious, the faster an outbreak spreads. Knowledge of this key epidemiological parameter is helpful not only in reducing local transmission but also in understanding presymptomatic transmission.

2. PAXLOVID REBOUND The US FDA has requested that Pfizer conduct a study examining an extended course of its antiviral Paxlovid among individuals who experience a rebound of COVID-19 after taking an initial 5-day course. The FDA wants to know if a second 5-day course of the antiviral would help prevent disease rebound, and has requested that Pfizer produce initial results of such a trial by September 30, 2023. While Pfizer claims that disease rebound following Paxlovid treatment remains rare, several high-profile cases have prompted the FDA’s request for further study into the phenomenon. 

3. US BOOSTER CAMPAIGN Following recent news regarding the authorization of variant-adapted SARS-CoV-2 vaccine boosters in the UK and applications for emergency use authorization (EUA) of BA.4/BA.5 boosters in the US (both Pfizer-BioNTech and Moderna), US government officials have signaled that variant-adapted booster doses could be available for individuals aged 12 years and older by early September. The bivalent vaccines will target both the original strain of SARS-CoV-2 and both the BA.4 and BA.5 sublineages (since they share common mutations to the spike protein).

While human clinical trials have not yet been conducted, the agency’s Director of the Center for Biologics Evaluation and Research (CBER), Dr. Peter Marks, indicated that he is “extremely confident” that the trials will demonstrate the candidate boosters to be safe and efficacious. In contrast to regulatory review of previous SARS-CoV-2 vaccine candidates, the FDA is not waiting on the completion of human clinical trials. Rather, the agency will base their assessment primarily on data from animal models and previous clinical trial data on BA.1-adapted bivalent candidate vaccines, a process similar to how the FDA reviews seasonal influenza vaccines. Clinical trials for the candidate boosters in humans are expected to begin this month. Reportedly, the FDA does not intend to convene its Vaccines and Related Biological Products Advisory Committee (VRBPAC) to discuss the candidate boosters; however, the CDC’s Advisory Committee on Immunization Practices (ACIP) has tentatively scheduled a meeting for September 1-2 in anticipation of a FDA decision. 

Some experts have expressed doubt regarding the need for a BA.4/BA.5-specific booster, as it may provide little additional protection for the millions of people who have already been exposed to one of those variants. Similarly, antibodies generated to protect against BA.4/BA.5 may not provide sufficient protection against other emerging variants, such as BA.2.75. While some experts are concerned that the abbreviated regulatory review risks increasing vaccine hesitancy and mistrust among the public, others argue that it is critical to make variant-adapted boosters available quickly, to provide protection before the virus evolves further and new variants emerge.

(J. Harris: I plan to follow this vaccine closely.)

4. Moderna sues Pfizer and BioNTech over coronavirus vaccine patent (Washington Post) Moderna sued Pfizer and its German partner BioNTech on Friday, alleging the rival firms improperly used its foundational technology in developing their coronavirus vaccine. The suit sets up a legal battle between the most prominent companies that helped curb the coronavirus pandemic in the United States by developing highly effective shots in record time. “We believe that Pfizer and BioNTech unlawfully copied Moderna’s inventions, and they have continued to use them without permission,” Moderna Chief Legal Officer Shannon Thyme Klinger said in a company news release. The company said it filed suits in U.S. District Court in Massachusetts and in Germany, where BioNTech is headquartered.

BECKERS reports:

1. 3 medications fail as possible COVID-19 treatments

2. Student debt relief’s effect on physicians, nurses: 5 notes

(J. Harris: Would that we could give them some relief while also requiring that they serve where they are most needed for a prescribed period of time.)


Fall boosters: An update

(J. Harris: Good read.)


Nirmatrelvir Use and Severe Covid-19 Outcomes during the Omicron Surge

”…Among patients 65 years of age or older, the rates of hospitalization and death due to Covid-19 were significantly lower among those who received nirmatrelvir than among those who did not. No evidence of benefit was found in younger adults.”


1. America’s Fall Booster Plan Has a Fatal Paradox

”…we might finally be getting inoculations that are well matched to the season’s circulating strains…..America is still stuck on … two very shaky assumptions, perhaps both doomed to fail: that the shots can and should sustainably block infection, and that “people will actually go and get the vaccine,..In terms of both content and timing, the fall shot will be one of the most important COVID vaccines offered to Americans since the initial doses… COVID vaccines, like most others, are best at staving off severe disease and death; against BA.5 and its kin, especially, that protection is likely to be durable and strong. But those same shields will be far more flimsy and ephemeral against milder cases or transmission, and can only modestly cut down the risk of long COVID. And when partnered with a compromised or elderly immune system, the shots have that much less immunological oomph…The U.S. needs people to take this vaccine because it has nothing else. But its residents are unlikely to take it, because they’re not doing anything else…Shots, to be abundantly clear, are essential to building up a properly defensive anti-COVID wall. But they are not by themselves sufficient to keep invaders out. Like bricks stacked without a foundation or mortar, they will slip and slide and crumble. Nor is a wall with too few bricks likely to succeed: If the goal is to preemptively quell a winter case surge, “a booster that will have maybe 30 to 40 percent uptake is not something we can expect to have a huge population-level impact,..”

(J. Harris: My personal plan is to take one of the modified vaccines even though they have not been well studied on humans. The basic vaccine has been studied and it works and is as safe as most any other vaccine. I don’t know if I will “Mix and Match” and take Moderna after have had 4 jabs of Pfizer with satisfactory results.)




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