A new study finds that early infections with the delta variant carry 1,000 times the viral load of infections from previous versions of the coronavirus; what new lab research reveals about vaccines' effectiveness against the delta variant; and more in this week's roundup of Covid-19 news.

• The delta variant replicates much more quickly in people's respiratory tracts than does the original version of the virus, according to a new study. For the study, researchers from the Guangdong Provincial Center for Disease Control and Prevention compared the levels of the virus in 62 people involved in the first delta variant outbreak in mainland China with the levels of the virus in 63 Covid-19 patients infected in 2020 with an earlier version of the virus. The delta variant patients had an average of 1,000 times more viral copies in their respiratory tract at the time of their first positive test, researchers said. In addition, the study found that someone infected with the delta variant has detectable levels of the virus after just four days, compared with six days among those infected with an earlier version of the virus. The findings indicate that someone infected with the delta variant is likely to become contagious sooner. (Doucleff, "Goats and Soda," NPR, 7/8)

• People who are only partially vaccinated against the coronavirus may not have sufficient antibody levels to protect against the delta variant, according to a recent study in Nature. For the study, researchers examined how well antibodies generated either by Covid-19 infections or through vaccinations could neutralize four different coronavirus variants: alpha, beta, delta, and a "reference variant" similar to the original version of the virus. The researchers found that only 10% of blood samples from people who had received one dose of either the Pfizer-BioNTech or AstraZeneca vaccines were able to neutralize the delta or beta variants in lab experiments—in contrast to the 95% of blood samples from people who had been fully vaccinated. According to the study, the findings suggest the delta variant has mutations that enable it to evade some of the neutralizing antibodies produced by either prior infection or vaccination. (Schnell, The Hill, 7/8; Achenbach, Washington Post, 7/8)

• Despite concerns that the delta variant may evade some vaccine protection, public health authorities are emphasizing that fully vaccinated people gain significant immunity. For instance, Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, recently cited data showing that the Pfizer-BioNTech vaccine, when fully administered, is about 80% effective at preventing infection with the delta variant, 88% effective at preventing symptomatic infection, and 96% effective at protecting against hospitalizations from the coronavirus. Similarly, Moderna officials have said research indicates that the company's Covid-19 vaccine has shown "promising protection in a lab setting" against the delta variant and other variants. And a Johnson & Johnson (J&J) press release from earlier this month states that the company's single-dose Covid-19 vaccine protects individuals against the coronavirus for at least eight months, with "strong, persistent" protection against the delta variant in particular. "It's so easy to get vaccinated," Fauci said of the available vaccinations. "Viruses don't mutate if they can't replicate, and you can prevent them from replicating by vaccinating enough people so that the virus has nowhere to go." (Kelly, NPR, 7/8; NBC10 Boston, 7/12)

• Federal regulators earlier this month cleared an additional 15 million doses of J&J's Covid-19 vaccine for distribution, according to the New York Times. The Baltimore factory that produced the vaccine—which has been shut down since April, after production problems caused 75 million doses to be contaminated—is expected to remain closed for several more weeks as its operator, Emergent BioSolutions, changes its manufacturing practices, sources told the Times. The newly released doses bring the total number of J&J vaccine shots approved from the plant to about 40 million, according to the Times. Although the Biden administration has not announced plans for the new J&J doses, they will likely be exported to other countries where vaccine supplies remain scarce. White House officials have said some countries have specifically requested the single-dose J&J vaccine because it is easier to store and some people prefer to receive just one shot. Currently, 27 countries have used the J&J vaccine, with 12.5 million people in the United States having received a dose. (LaFraniere/Weiland, New York Times, 7/2)

• New research published in Nature has identified a eight amino acids that are targeted by antibodies in the blood of some people vaccinated with AstraZeneca's Covid-19 vaccine, the Wall Street Journal reports—findings researchers said could shed light on what causes the rare blood clots associated with that vaccine and the J&J vaccine. According to the Journal, in rare cases, people who receive either AstraZeneca or J&J's vaccine experience an autoimmune reaction in which antibodies bind to a blood component called platelet factor 4 (PF4), causing clusters to form that themselves activate more platelets, a process that accelerates and triggers simultaneous bleeding and clotting. Mortimer Poncz, the pediatric-hematology division chief at the Children's Hospital of Philadelphia, who was not involved in the study, said the findings could help doctors quickly identify the blood clotting issue and help researchers understand what causes the condition. Meanwhile, the companies behind the J&J and AstraZeneca vaccines are both looking into potentially modifying their shots to reduce the risks of blood clots. (Strasburg, Wall Street Journal, 7/7)

• Maryland last week announced that 100% of Covid-19 deaths in the state in June had occurred in people who were not vaccinated. In addition, Michael Ricci, communications director for Maryland Gov. Larry Hogan (R), said 95% of new Covid-19 cases and 93% of new hospitalizations had occurred among unvaccinated people, The Hill reports. More broadly, on NBC's "Meet the Press," Fauci said that 99.2% of Covid-19 deaths nationwide in June were among those who were unvaccinated. According to The Hill, experts say instances of hospitalization and death from Covid-19 are now largely avoidable in the United States due to the wide availability of vaccines, and health officials are urging unvaccinated individuals to get their shots. (Sullivan, The Hill, 7/6)

• Cancer patients can develop antibodies against Covid-19 after two doses of the Pfizer-BioNTech vaccine, according to a study from Israeli researchers published in JAMA Oncology. According to the researchers, only 29% of cancer patients in the study had detectable antibodies after the first dose of the vaccine, much lower than 84% of controls who were seropositive, but the number climbed to 86% after the second dose. "Although the immunogenicity pattern was gradual and slower than in the noncancer population," the researcher said, "after the second dose most patients were seropositive and no documented cases of Covid-19 infection were determined." (Bassett, MedPage Today, 7/8)