Monovalent COVID booster protects well against Omicron, but it wanes over 6 months

News brief
Topics
COVID-19

SARS-CoV-2 antibodiesThe monovalent (single-strain) COVID-19 vaccine booster was 74% effective against Omicron infection compared with the primary vaccine series for 3 months, but protection waned to 42% from 3 to 6 months and 36% after 6 months, estimates a study published yesterday in Influenza and Other Respiratory Viruses.

Marshfield Clinic researchers estimated relative vaccine effectiveness (rVE) of a monovalent COVID-19 vaccine booster compared with the primary series among 883 participants aged 5 years and older living in Wisconsin from January to July 2022.

The study spanned the predominance of the SARS-CoV-2 Omicron variant, primarily the BA.2 and BA.5 substrains, and was conducted before the availability of the updated bivalent (two-strain) COVID-19 booster.

A total of 625 (71%) received a booster, while the remainder completed only the primary series. Participants completed a symptom survey and submitted a nasal swab for polymerase chain reaction (PCR) testing each week and when they had at least one COVID-like symptom.

Of 219 (25%) COVID-19 infections, 97 occurred after receipt of the primary series, and 122 occurred after a booster. Overall rVE was 51%, regardless of previous infection status or the presence of an immune-compromising condition.

Routine vaccination needed

Fifteen days to 3 months after booster receipt, rVE was 74%, dropping to 42% at 3 to 6 months and 36% after 6 months. The rVE of a second monovalent booster compared with a single booster was 24% among participants aged 50 and older—the only participants eligible for a second booster—but the 95% confidence interval ranged from –40% to 61%.

Increasing bivalent booster uptake should be a priority to increase protection likely lost due to waning immunity.

The results, the authors said, confirm that vaccine-induced protection against COVID-19 infection is temporary and influenced by evolving pandemic conditions.

"Increasing bivalent booster uptake should be a priority to increase protection likely lost due to waning immunity and antigenic change of circulating viruses," they wrote. "As is the case with influenza, routine vaccination, and regular evaluation of vaccine composition will be necessary to address ongoing SARS-CoV-2 transmission."

Study finds benefits in short-course antibiotics for ventilator-associated pneumonia

News brief
Topics
Antimicrobial Stewardship
Pneumonia

Patient on ventilatorA review and meta-analysis of randomized controlled studies (RCTs) found that short-course antibiotic therapy for ventilator-associated pneumonia (VAP) did not result in increased recurrence or relapse, French researchers reported yesterday in eClinical Medicine.

The review identified five relevant studies comparing treatment for VAP with short-course (8 days or less) versus long-course (10 to 15 days) antibiotic therapy. Despite guidelines for VAP treatment, the optimal antibiotic duration remains unclear, especially for VAP caused by non-fermenting gram-negative bacteria (NF-GNB).

The primary end point for the meta-analysis was recurrence and relapse of VAP. Secondary end points included 28-day mortality, mechanical ventilation duration, number of extra-pulmonary infections, acquisition of multidrug-resistant (MDR) pathogens, and length of intensive care unit (ICU) stay.

The five studies included 1,069 patients, with 530 in the short-course group and 539 in the long-course group. There was no significant difference between short-course therapy (odds ratio [OR], 1.48; 95% confidence interval [CI], 0.96 to 2.28) and long-course therapy (OR, 1.45; 95% CI, 0.94 to 2.22) for recurrence and relapse of VAP. The findings were similar for VAP caused by NF-GNB (OR, 1.90; 95% CI, 0.93 to 3.33 vs OR, 1.76; 95% CI, 0.93 to 3.33). No difference was found between the two groups for 28 day-mortality, mechanical ventilation duration, number of extra-pulmonary infections, acquisition of MDR pathogens, and length of ICU stay. However, short-course therapy significantly increased the number of antibiotic-free days.

Tailored strategies (including clinical and biological endpoints) should be tested in RCTs.

The authors note that while the results suggest that short-course therapy for VAP is preferrable because it reduces exposure to antibiotics, the findings are limited by the small number of trials included in the meta-analysis, the heterogeneity of the studies, and the differences in antibiotics used by the two groups.

"Tailored strategies (including clinical and biological endpoints) should be tested in RCTs in order to individualize antibiotic duration treatment," they wrote.

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