Who should get the monkeypox vaccine? What to know as Mass. limits shots to one dose only

With the monkeypox vaccine in short supply and cases rising quickly, state health officials have instructed providers to schedule only the first of two doses.

The goal is to give some protection to as many people as possible until more vaccine becomes available in the hope of reining in a fast-spreading virus that has caught the nation by surprise. The vaccine, known as Jynneos, is normally given in two doses 28 days apart, but health officials said the second shot would still be effective if delayed.

In a directive that took effect Monday, the state Department of Public Health told clinics that offer the vaccine to honor any already-scheduled second-dose appointments, but to refrain from making new ones.

The shift in strategy means almost doubling the number of people who can get vaccinated at a time when case numbers are soaring, said Dr. Paul Biddinger, medical director for emergency preparedness at Mass General Brigham, who has been advising the state health department. As of last week, Massachusetts had reported 157 monkeypox cases, with 42 diagnosed between July 28 and Aug. 3.

A single dose “is still highly effective at decreasing transmission,” he said. “There is data saying the immune response after a single dose starts to wane after two years. Certainly delaying [the second dose] a couple of months is unlikely to have major clinical significance,” Biddinger said.

Dr. Cassandra Pierre, Boston Medical Center’s associate hospital epidemiologist and medical director of public health programs, said she agreed with the decision, despite doubts about the data on how long single-dose immunity lasts.

“We’re really trying to sprint to prevent this infection from becoming endemic,” she said.

State health officials said that a single dose provides substantial, rapid protection from monkeypox infection, and the second dose will provide long-term immunity even if given months later.

The new rules make one important exception. Second doses may be administered to people whose immune systems are compromised, such as those who are recent organ transplant recipients, undergoing chemotherapy, or suffering from an HIV infection that is not suppressed.

Meanwhile, the Biden administration on Tuesday authorized stretching the supply even further by administering just one-fifth of a dose between the layers of the skin rather than into the fat beneath it as is currently done. One study found that the lower-dose intradermal injection induced an immune response comparable to that of the standard method. But health care workers may require training in the new method.

All doses of Jynneos are being distributed through the US Centers for Disease Control and Prevention. Massachusetts has received several shipments since July 5, with a total of 16,251 doses, but does not expect any more until the fall. As of Aug. 3, a total of 5,875 doses had been administered in the state.

Here are answers to some common questions about the monkeypox vaccine.

Who is eligible to receive the vaccine?

Anyone who lives or works in Massachusetts and who has had contact with a person diagnosed with monkeypox is eligible. Also eligible are people who in the past 14 days had sex with someone diagnosed with monkeypox or had multiple sexual partners in an area where monkeypox cases have occurred.

Monkeypox has been spreading in networks of men who have sex with men, but anyone can catch and transmit it.

For more details, visit the state’s website: mass.gov/info-details/monkeypox-vaccination.

Where can people get the vaccine?

The state is distributing the vaccine to 14 clinics, and you must make an appointment to get the shot. The clinics are listed here: mass.gov/info-details/monkeypox-vaccination#how-to-obtain-vaccine-.

Are these clinics able to meet the demand? And are they reaching everyone who needs the vaccine?

Some are struggling more than others.

Dr. Genevieve Daftary, medical director of practice at the Codman Square Health Center in Dorchester, said a big challenge is staffing. “We’ve been able to commit to three four-hour sessions” each week, she said. Daftary hopes to open up more hours by hiring per-diem nurses through an agency.

Dr. Mireya A. Wessolossky, medical director at AIDS Project Worcester, said calls seeking the vaccine “are increasing as we speak.”

With 20 hours worth of vaccination appointments available per week, Wessolossky said, “We are scheduled all the way to September. … We are going to see how we can add more hours to accommodate the demand.”

Biddinger said that Mass General Brigham has been able to vaccinate every eligible person who has sought the shot, but he believes many more qualify for the vaccine but haven’t received it.

Boston Medical Center’s waiting list for monkeypox vaccine has shrunk from 800 to 100 people, and will be down to zero soon, Pierre said, now that the clinic is fully staffed. “We are meeting the demand,” she said.

But she worries that there are many other people who don’t realize they’re at risk or have poor access to the health care system.

Does the smallpox vaccine work against monkeypox?

It does, but it’s “much more challenging to deliver,” Biddinger said. The vaccine contains a replicating virus, so people who administer it have to be vaccinated themselves, and anyone who takes it can’t be around people who have weakened immune systems or other conditions, he said.

Known as ACAM2000, the vaccine is kept in the Strategic National Stockpile in case smallpox is ever used as a biological weapon. It is recommended for military personnel and people who work in laboratories where they may be exposed to related viruses. Biddinger said he is not aware of anyone using the smallpox vaccine to combat the monkeypox outbreak.

As for people who were vaccinated against smallpox as children, Biddinger said it’s not known for sure whether they are immune to monkeypox, but they probably have some protection against severe illness.

Can the monkeypox outbreak be brought under control or is it too late?

“I don’t think we know yet,” Biddinger said. “It is reassuring that the disease continues to be transmitted in the ways we knew before this outbreak” — primarily through close skin-to-skin contact. Improved education about how to avoid infection and an increasing vaccine supply this fall and winter “make me hope we can get this under control, but right now the numbers are not headed in the right direction,” he said.

Wessolossky, of AIDS Project Worcester, expressed optimism. “I think we’ll get it [under control],” she said. The declaration of a public health emergency last week may ease access to a medication, known as TPOXX, that shortens the duration of sickness and infectiousness.

Pierre, of Boston Medical Center, was on the fence. “I’m hopeful,” she said, “but still worried.”

Felice J. Freyer can be reached at felice.freyer@globe.com. Follow her @felicejfreyer.