Covid-19: Vaccines appear weak at blocking Omicron infection, says study

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

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/BioNTech vaccine against Omicron. Their models suggest that early after two doses of an mRNA vaccine from Pfizer/BioNTech or Moderna, efficacy against symptomatic infection from Omicron is only about 30 per cent, down from about 87 per cent 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 per cent, “which is similar to the protection of individuals with waned immunity against the Delta variant (43%),” Kilpatrick said.

ALSO READ:

• Canada could soon see rapid surge in Covid-19 cases as Omicron spreads locally

• No plans for any further Covid restrictions in UK, says Health Secretary Sajid Javid

• Covid-19: First patient dies of Omicron in UK, says Boris Johnson

“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 per cent for recent mRNA vaccination against Omicron, 67 per cent for waned immunity, and 91 per cent 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.”

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 analysed 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 per cent after the first vaccine dose, the researchers reported. It was unclear whether this improvement continued between the first and second doses. A further 9 per cent 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 Ayoubkani 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, Pfizer/BioNTech, or Moderna.

“However,” Ayoubkani 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.”

In some patients on immunosuppressive drugs, Covid-19 vaccines may induce protective antibodies without inducing good second-line immune defences, 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 recognise 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 per cent — 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?

• Europe