On November 19, 2024, the California Department of Public Health issued a health advisory that California had confirmed the first case of mpox infection from Clade 1B mpox (monkeypox) virus (California Department of Public Health (CDPH)a, 2024). While the overall risk of Clade I affecting the general population in California continues to be low, this case follows the August 14, 2024 World Health Organization declaration identifying mpox as a public health emergency of international concern. An alarming number of cases of Clade 1B in the Democratic Republic of Congo (DRC) and reported cases in nearby countries, such as Burundi, Rwanda, and
Kenya have given rise to concerns of further spread across and beyond central Africa (World Health Organization, 2024). Africa has recorded 50,840 cases of and 1,083 deaths from mpox this year alone (Voice of America, 2024). Although its spread seems to be abating in the DRC recently, travel-related cases of Clade 1B have been reported in Sweden, Germany, India, Thailand, and the UK (Centers for Disease Control and Prevention (CDC)a, 2024). A few additional cases from household transmission have followed the initial case of Clade 1B reported at the end of October in the UK (BBC, 2024). Total confirmed cases through October 1, 2024 numbered 34,063 (Our World In Data, 2024), with 2,404 cases reported year to date as of November 2 (CDCb, 2024).
In its August 2024 assessment, the CDC deemed the risk of mpox in the US as low to moderate among men who have sex with men (MSM) that have more than one sex partner and to sexual partners of MSM, irrespective
of gender (CDCc, 2024). By moderate, they mean there is potential for many people to be exposed or for a substantial proportion of the population or segments within it to experience severe disease (CDCd, 2024). An alternative and more recent November 4th risk assessment was made by the Center for Outbreak Response Innovation. Under the scenario in which both Clades I and II increase in spread through Africa, they believe that the health risk to the MSM community, as well as to sex workers, in the United States is moderate (Center for Outbreak Response Innovation, 2024). The possible impact of a Clade I outbreak on the US is uncertain, with only 1 confirmed case in the U.S.. However, better medical care and access to vaccination and therapeutics are likely to lead to lower morbidity and mortality, in comparison to the DRC.
From May 2022 to January 2023, the month that the US mpox public health emergency was declared over, close to 1.2 million vaccine doses had been administered in 57 jurisdictions across the US (Owens et al., 2023). Full vaccination against mpox requires two doses, whether delivered by subcutaneous or intradermal injection. In August 2022, the Food and Drug Administration approved the option to administer the vaccine as an intradermal injection to conserve doses. At the end of January 2023, one- and two-dose vaccination coverage among persons at risk of mpox in the US were 37% and 23%, respectively (Owens et al., 2023). Among California residents who initiated the mpox vaccination series between May 2022 to March 2023, 64.5% completed the series as of the end of April 2023 (Salih et al., 2023).