4 COVID vaccine doses best prevent critical Omicron BA.5, even after BA.1/BA.2 infection

News brief

SARS-CoV-2 spike proteinsFour COVID-19 booster doses were the most effective way to prevent critical Omicron BA.5, regardless of previous infection status, according to a nationwide study published late last week in JAMA Network Open.

South Korean researchers used the Korea COVID-19 Vaccine Effectiveness data set to estimate the protection conferred by vaccination and previous Omicron BA.1 or BA.2 infection against BA.5 infection and critical illness among 3,415,980 who tested positive for the virus and an equal number of matched controls from Aug 1 to 31, 2022. The average age was 40.2 years, and 53.9% were female.

2-dose VE low in all groups

Vaccine effectiveness (VE) of four doses of COVID-19 vaccine against BA.5 infection among COVID-naïve participants was 16.1%, while it was 89.5% and 94.3% among those previously infected with BA.1 and BA.2, respectively.

VE of two doses against critical BA.5 was low in all groups, including COVID-naïve participants (41.5%) and those previously infected with BA.1 (53.1%) and BA.2 (50.0%). But four-dose VE against critical BA.5 was 90.9% among COVID-naïve participants and 93.9% and 92.9% among those with previous BA.1 and BA.2 cases, respectively.

The observation that the protection against critical BA.5 infection depends more on 4-dose booster, rather than previous BA.1 or BA.2 infection, highlights the importance of booster vaccination.

The authors cautioned that some infections may have been missed, and protection from previous infection could have been overestimated if exposed participants sought testing more often than their unexposed peers.

"Importantly, the observation that the protection against critical BA.5 infection depends more on 4-dose booster, rather than previous BA.1 or BA.2 infection, highlights the importance of booster vaccination," they concluded.

Quick takes: Resistant E coli in Germany, multidrug-resistant gonorrhea, bloodstream infections in Sweden

News brief

The latest issue of Eurosurveillance included three reports on antibiotic-resistant infections in Europe:

  • German researchers reported on the rapid and ongoing spread of carbapenemase-producing Escherichia coli in Germany. Whole-genome sequencing (WGS) of 222 E coli isolates producing the New Delhi metallo-beta-lactamase 5 (NDM-5) gene revealed that incidence rose in Germany from 2013 to 2019 largely because of the increased prevalence of isolates belonging to multiple sequence types (STs), mainly the international high-risk clones ST167, ST410, ST405, and ST361. The researchers say available evidence suggests the increased number of cases is being driven by local clusters and that NDM-5–producing E coli appear to be spreading in the community through multiple sources and transmission routes.
  • Researchers with the World Health Organization (WHO) Collaborating Centre for Gonorrhoea and Other Sexually Transmitted Infections (STIs) reported on a multidrug-resistant gonorrhea infection identified in a female sex worker in September 2022. The woman was treated with ceftriaxone, which is the last-remaining recommended treatment for Neisseria gonorrhoeae infections, but did not return for test of cure. Antimicrobial susceptibility testing revealed the isolate was resistant to ceftriaxone, cefixime, cefotaxime, ciprofloxacin, tetracycline, and benzylpenicillin, and WGS identified a mutation to the penA-60.001 allele that confers ceftriaxone resistance. The analysis also found that the isolate belongs to a genomic lineage that to date has been antibiotic susceptible, "showing that strains across the gynecoccal phylogeny can develop ceftriaxone-resistance," the researchers wrote.
  • Also in Sweden, a retrospective study on bloodstream infection (BSI) incidence in southern Sweden found an average annual increase of 3.0% from 2006 to 2019. The most frequent bacteria isolated were E coli (27% of isolates) and Staphylococcus aureus (13%). Of the 17,734 isolates with resistance data, 14.8% were resistant to at least one of the three antibiotics tested: ciprofloxacin (11%), cefotaxime (6.5%), and gentamicin (4.7%). Over time, the proportion of resistant BSI isolates rose from 12.1% to 17.4% for any antibiotic. Patients aged 80 and older had the highest BSI incidence and a disproportionate increase. "Any preventive measures should prioritise the oldest patients," the study authors wrote.

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