Vaccines appear weak at blocking Omicron, better against severe disease - Reuters

Vials with Pfizer-BioNTech and Moderna coronavirus disease (COVID-19) vaccine labels are seen in this illustration picture taken March 19, 2021. REUTERS/Dado Ruvic/Illustration

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Dec 13 (Reuters) - The following is a summary of some recent studies on COVID-19. They include research that warrants further study to corroborate the findings and that has yet to be certified by peer review.

Vaccines appear weak vs Omicron infection, better vs severe disease

Vaccine effectiveness against symptomatic infection from the Omicron variant of the coronavirus is likely to be much lower than against earlier variants, but they may still offer substantial protection against severe disease, a new analysis suggests.

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Billy Gardner and Marm Kilpatrick from the University of California, Santa Cruz developed computer models incorporating data on COVID-19 vaccines' efficacy against earlier variants and initial data on the Pfizer (PFE.N)/BioNTech vaccine against Omicron. Their models suggest that early after two doses of an mRNA vaccine from Pfizer/BioNTech or Moderna (MRNA.O), efficacy against symptomatic infection from Omicron is only about 30%, down from about 87% versus Delta, they reported on Sunday on medRxiv ahead of peer review. Protection against symptomatic infection is "essentially eliminated" for individuals vaccinated more than four months earlier. Boosters restore protection to about 48%, "which is similar to the protection of individuals with waned immunity against the Delta variant (43%)," Kilpatrick said.

"Importantly, protection against severe disease is much higher" for all categories: recently vaccinated, waned, or boosted. "We estimated that protection against severe disease was 86% for recent mRNA vaccination against Omicron, 67% for waned immunity, and 91% following 3rd dose boosters," Kilpatrick said. "There are still no direct estimates of vaccine effectiveness for severe disease from any country yet, so our estimates cannot be compared to direct estimates yet."

COVID-19 vaccines may reduce long COVID burden

COVID-19 vaccines may contribute to a reduction in the health burden of long COVID, new findings suggest.

Researchers analyzed survey responses from 28,356 adults ages 18 to 69 from across the UK who had previously had COVID-19, nearly one-quarter of whom had reported troublesome lingering symptoms. The likelihood that participants would report long COVID symptoms at least 12 weeks after infection fell by 13% after the first vaccine dose, the researchers reported on Thursday on medRxiv ahead of peer review. It was unclear whether this improvement continued between the first and second doses. A further 9% reduction in the odds of persistent symptoms after the second vaccine dose "did appear to be sustained, at least over the follow-up period of 67 days on average," said study leader Daniel Ayoubkhani of the UK Office for National Statistics. The same was true for long COVID symptoms severe enough to hamper daily activities, and the pattern was similar regardless of whether participants received vaccines from AstraZeneca (AZN.L), Pfizer/BioNTech, or Moderna.

"However," Ayoubkhani noted, "we can't say from this study if, or how, vaccination caused the observed changes in symptoms, and more follow-up time is needed to assess whether the improvement will be sustained in the longer term and the impact of booster doses and new variants."

Good antibody levels from vaccines no guarantee of other immune defenses for some

In some patients on immunosuppressive drugs, COVID-19 vaccines may induce protective antibodies without inducing good second-line immune defenses, leaving them at risk for severe illness if they do become infected, researchers say.

Vaccines reduce the severity of illness by inducing T cells in the immune system to recognize and eliminate virus-infected cells. In 303 patients on immune-suppressing therapies for inflammatory bowel disease, researchers used a new molecular measurement tool to count the numbers of antiviral T cells induced by COVID vaccines. "Overall, a substantial number of vaccinated patients - about 20% - had minimal antiviral T cell levels, even though most had high antiviral antibodies," said study leader Jonathan Braun of Cedars-Sinai Medical Center in Los Angeles.

Age, sex and specific immunotherapies might be associated with patients' T-cell response to the vaccines, but the bottom line is that antibody levels after vaccination do not necessarily predict T cell responses, his team said in a report posted on Wednesday on medRxiv ahead of peer review. Levels of antiviral T cells are not often measured, Braun said, leaving open important questions. Among them: How frequent are vaccinated individuals with low antiviral T cell levels in the general population? and, Do boosters help such individuals elevate their antiviral T cell levels?

Click for a Reuters graphic on vaccines in development.

(This story corrects spelling of Dr. Ayoubkhani's name in second item)

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Reporting by Nancy Lapid; Editing by Bill Berkrot

Our Standards: The Thomson Reuters Trust Principles.

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