Mpox outbreak

America’s mpox outbreak “is not over” and could see a resurgence over the coming months, the Centers for Disease Control and Prevention said Monday, ramping up their warnings after reports of “ongoing community transmission” of the virus around the country. 

The CDC’s new alert for doctors and health authorities comes ahead of new vaccine effectiveness data expected to be released by the agency. 

It also follows a cluster of infections in the Chicago area from mpox, formerly called monkeypox, many in fully vaccinated residents. While none were hospitalized, potentially thanks to their two doses, authorities are now investigating a range of potential explanations for the breakthrough cases. 

“Spring and summer season in 2023 could lead to a resurgence of mpox as people gather for festivals and other events,” the CDC said in the alert, echoing an earlier prediction by the agency’s modelers.

At least 36 new cases have been diagnosed over the past month around the country, according to figures published by the CDC last week. This includes infections during the days leading up to April 26, which officials had previously heralded as a record week of no new infections.

“There was actually a time on our website where the average daily number of cases was zero over a seven-day period. But we know that that wasn’t actually the case, because then subsequently cases were reported,” the CDC’s Dr. Chris Braden said last week at an emergency meeting convened by the National Coalition of STD Directors. 

Braden said the agency is still seeing far fewer cases reported than at the peak of last year’s outbreak, which saw hundreds diagnosed each day. But Braden added that federal authorities are now “very concerned that we are going to see more of what Chicago has experienced.”

Spokespeople for health departments in New York City and California tell CBS News they are closely tracking sporadic new cases, but have so far not identified a resurgence.

“We also see some wastewater detections in a number of different jurisdictions that may be a harbinger of things to come. So we are very concerned,” said Braden.

Breakthrough infections

Braden said a number of reasons could explain the recent uptick of breakthrough infections in Chicago.

One is the possibility that the mpox virus may have mutated to evade the vaccine’s immunity. While viruses like mpox generally evolve far slower than other pathogens — including SARS-CoV-2, the virus that causes COVID-19 — authorities had tracked unusual jumps in its genome during last year’s outbreak, including changes that led to the virus dodging some tests.

A spokesperson for Chicago’s health department told CBS News that the city is currently working with the CDC on sequencing virus samples collected from the cluster of cases.

Investigators also want to know if cases may have all been vaccinated from the same batch.

“Specific vaccine doses or lots may be compromised. So when we have a cluster of people who had been vaccinated but now are infected, we want to look at that to see if there are common lots among them,” Braden said.

Some of the CDC’s outside vaccine experts had also wondered if last year’s approach of using smaller “intradermal” doses to stretch supplies last year might risk lower effectiveness. It is unclear how the patients in this cluster were vaccinated.

The cluster could be the result of random chance, a sign that authorities have been reaching vaccines to the communities most at risk of infection or simply that vaccinated cases are more likely to be detected by health authorities.

“Vaccinated people may be among those in continuous care, and more likely to be diagnosed, and then be part of our surveillance of cases. And so it may be a surveillance artifact in that way,” said Braden.

The vaccine may also be waning in immunity faster than authorities had hoped or lower than previously estimated. Braden said the CDC has three new vaccine-effectiveness studies that are expected out this week.

“We are going to be seeing releases of more VE data. And the view into that data is that it’s about as we expect, based on what has already been published,” the White House’s Dr. Demetre Daskalakis said at the NCSD meeting.

Daskalakis pointed to CDC’s preliminary vaccine effectiveness estimates from last year, which put two doses of the mpox vaccine at around 69% effectiveness.

“The confidence intervals go from 41% all the way to 81%. So I think we have to have a lot of humility,” said Daskalakis.