Health officials urge caution amid potential re-emergence of mpox as summer arrives

As summer festival season arrives, public health authorities are warning of a potential resurgence of mpox infections as vaccine effectiveness appears to wane, often in the absence of a second recommended dose.

Recently, the U.S. Centers for Disease Control and public health officials in San Diego County have highlighted a mpox outbreak in Chicago which, according to a May 18 briefing from the CDC, involved 21 new infections.

“What’s really unique about this cluster is that most of the cases are in people who have had one or both vaccine doses,” said Dr. Demetre Daskalakis, deputy White House mpox coordinator.

San Diego County has documented four instances where a vaccinated resident later became infected, but all were reported in 2022. The region, said Dr. Ankita Kadakia, deputy public health officer , has not had a new case reported since February, but outreach efforts to the communities that are most at risk is underway.

“Although we have not seen the same situation in San Diego that has been observed in Chicago, we still want to take a proactive approach,” Kadakia said. “We know that summer is coming up and travel is coming up, and there are a lot of festivals and outdoor events where people will be gathering.

“We just want to, you know, give a reminder to our local community about the availability of mpox vaccination, and we also have testing available if somebody is concerned.”

While vaccination, along with public messaging around transmission prevention, is credited with stopping the 2022 global outbreak, there is evidence that the vaccine is not a panacea.

According to the CDC, recent research estimates the effectiveness of the JYNNEOS vaccine at between 36 percent and 75 percent for a single dose and 66 percent to 86 percent for two doses, which is the recommended number.

It’s important to remember, said Dr. David M. Smith, head of the Division of Infectious Diseases and Global Public Health at UC San Diego, that this vaccine was designed to prevent smallpox infection. While the viruses that cause mpox, formerly called monkeypox, and smallpox are closely related, they are not identical and that, Smith said, is the likely reason for the difference in vaccine response.

“For smallpox, it is really good, like, you just need to get it once and you’re protected,” Smith said. “We thought that we would see the same using a smallpox vaccine for mpox, because there are so many similarities between the two, but now we’re seeing that while immunity did occur, it did work, now it’s waning.”

Though vaccine effectiveness research is showing that a second dose conveys a significant jump in immunity, many have not bothered to get that second dose.

Vaccination data show that about 750,000 Americans received a first dose, but only about 470,000 of those returned for a second shot. In San Diego County, a total of 14,681 residents had received at least one dose as of May 1, 2023, but only 9,520 returned for a second.

Thus far, no schedule for a booster dose has been approved for mpox to boost immunity as case rates begin to build. While the official recommendation for a second dose is 28 days after the first, Smith said there is no reason to think that completing the series can’t happen significantly outside that window.

That means, for those who got their first dose, but not their second, it’s possible to get an additional boost just as summer is starting.

“There is no great data with this vaccine showing that 28 days is optimal,” Smith said in an email. “Most of this recommendation is based on data from other vaccines.

“It is likely that doses given later outside the window will generate high levels of immune protection.”

Of course, there is plenty that can be done to avoid infection outside of vaccination.

The mpox virus spreads through intimate, most often sexual, contact between people. The World Health Organization indicates that 96 percent of cases are male with a median age of 34. Public health interviews have found that 84 percent of those willing to share their sexual orientation identified as men who have sex with men and, of those, nearly 8 percent said they were bixesual.

Though men are disproportionately affected, women are also in the crossfire, making up nearly 4 percent of cases.

Party settings with sexual contact are listed as the likely infection locations in 66 percent of cases.

That information tracks with the last global outbreak, which was reported to be connected to Pride events, which occur in cities worldwide.

The idea, said Kadakia, the county medical director, is to pay attention to safe sex messages while still celebrating as would be the case any other year.

“When we talk about limiting exposure, we still want people to go out and live their best lives, right?” Kadakia said. “It’s not about having to restrict themselves or, you know, not go out and enjoy the summer festivals or travel or whatever other activities they are participating in.”

Smith, who has treated several severe cases of mpox over the past year, added that it’s important for those who experience symptoms to come forward and get help. Severe cases can be very painful, and there is no reason to suffer without help.

“If you feel something, say something, I think that’s really the key,” Smith said.

According to the CDC, public health departments distributed more than 1.2 million doses of the JYNNEOS vaccine in the United States since the 2022 outbreak started, peaking at 460 new cases per day, infecting more than 30,000 and killing 42 across America.

Globally, more than 87,000 cases were confirmed with 143 deaths, according to the World Health Organization. From May 22 to May 28, according to the WHO, there has been a global increase in monkeypox activity with 96 cases detected that week compared to 51 cases one week earlier. To date, San Diego County has reported 474 cases, 18 hospitalizations and zero deaths.