The odds of SARS-CoV-2 infection were 6.2 times greater among household contacts during the Omicron variant wave than during periods dominated by other strains, with rates even higher in children, estimates a study published yesterday in Emerging Infectious Diseases.

A team led by researchers from the National Institute of Infectious Diseases in Tokyo analyzed COVID-19 case rates in a single city during four variant waves: July 1 to October 31, 2020 (before variants of concern), April 1 to 30, 2021 (Alpha), July 3 to August 15, 2021 (Delta), and January 3 to 23, 2022 (Omicron).

Health center staff interviewed COVID-19 patients, regardless of symptom status. Close contacts were tested for COVID-19, even if they were asymptomatic.

The team enrolled 1,057 COVID-19 patients and 3,820 contacts, including 123 patients and 530 contacts in the prevariant period, 246 patients and 998 contacts amid Alpha, 304 patients and 984 contacts during Delta, and 384 patients and 1,318 contacts during Omicron. Close contacts without polymerase chain reaction results were excluded.

3.6-times-higher rate among non-household contacts

COVID-19 rates during Omicron were 35.0% for household contacts and 15.1% for non-household contacts. After adjustment for potential confounding factors, the odds of infection were 6.2 higher among household contacts and 3.6 times greater among other contacts amid Omicron than during the prevariant period.

The risk of infection rose significantly among household contacts aged 0 to 19 years, from 3% before variants of concern to 38% amid Omicron. Infection rates for non-household contacts in this age-group, however, were lower.

COVID-19 rates among household contacts 60 years and older declined 12% during Delta but rose 29% amid Omicron. Throughout all periods, the risk of infection from patients 60 and older was higher than among those in other age-groups.

A study today in Morbidity and Mortality Weekly Report looked at a recent cluster of 40 mpox cases in Chicago and suggests that vaccine protection may wane over time, but vaccinated patients do well recovering at home, and vaccination protects against severe mpox.

The cluster, identified from March 18 to June 12, 2023, was notable because in the previous 2 months the Chicago Department of Health received notice of only 1 mpox case. And 55% of case-patients in the cluster reported having completed the two-dose schedule of Jynneos mpox vaccine prior to their illness or had received one dose of ACAM2000, a smallpox vaccine that also prevents mpox.

The 40 laboratory-confirmed cases included 22 (55%), 5 (13%), and 13 (33%) patients who had received, respectively, either 2 doses of Jynneos or 1 dose of ACAM2000 vaccine, 1 Jynneos dose, or no vaccine.

Most of the case-patients reported being vaccinated against the virus in July or August 2022; the median interval from receipt of the second Jynneos vaccine dose to mpox diagnosis was 8.4 months.

Vaccine protection against more severe illness

Patients who received only one dose of Jynneos or no vaccines had a higher prevalence of lesions affecting the genital (43% versus 6%) or ocular (29% versus none) mucosa, the authors said.

"Preliminary medical record review indicates that vaccinated patients experienced self-limited illness, managed in outpatient settings," the authors wrote. None of the patients who had been vaccinated required hospitalization, compared to two unvaccinated patients who were admitted for treatment.

Although the cause of this cluster has not yet been determined, leading hypotheses include a potential high number of sexual exposures.

"Although the cause of this cluster has not yet been determined, leading hypotheses include a potential high number of sexual exposures in a network with many vaccinated persons, decreased vaccine effectiveness due to waning of humoral immunity, or vaccine mishandling or administration errors," the authors concluded.

Cidara Therapeutics, of San Diego, announced today that the US Food and Drug Administration (FDA) has granted fast-track designation for CD388, the company's novel drug for preventing influenza A and B in adults at high risk for severe influenza, including those for whom vaccines are either ineffective or not indicated.

Fast-track designation aims to facilitate the development and expedite the review of drugs to treat serious conditions with unmet medical needs. The purpose is to get key new drugs to patients earlier. Companies that are granted this designation are given the opportunity for more frequent interactions with the FDA, and, if relevant criteria are met, eligibility for Priority Review.

Cidara is developing CD388, a drug-Fc conjugate candidate, in collaboration with Janssen Pharmaceuticals.

"We are pleased that the FDA has granted Fast Track designation for CD388, which emphasizes the unmet need for effective new prevention options for the many individuals who are not adequately protected by available influenza vaccines," said Jeffrey Stein, PhD, Cidara president and CEO.

[The approval] emphasizes the unmet need for effective new prevention options for the many individuals who are not adequately protected by available influenza vaccines.

Cidara recently announced promising interim efficacy and safety data from an ongoing phase 2a study being conducted in cooperation with Janssen. The study is evaluating how well CD388 prevents infection from the influenza A H3N2 strain.