As of July 1st, 2022, the US Centers for Disease Control and Prevention (CDC) reported approximately 460 cases of monkeypox in the US, primarily among men who have sex with men. Germany, Spain, France and the UK have reported more cases per capita than the US. Monkeypox is a member of the Orthopoxvirus genus, a cousin of smallpox.

A person with monkeypox is infectious for 2-4 weeks via direct contact, person to person, from the rash and body fluids including saliva and sexual contact. The virus can be spread during pregnancy via the placenta. The pox virus can also be spread by touching items such as clothing that previously touched someone with the infection. Transmission via human milk is not known. Monkeypox can also be contracted from infected animals via a bite or scratch, or preparing meat from an infected animal.

There are 2 smallpox vaccines available to prevent monkeypox- JYNNEOS (also known as Imvamune or Imvanex) and ACAM2000. The JYNNEOS smallpox vaccine contains live virus that does not replicate efficiently, meaning that it is not expected to spread smallpox infection. This is the preferred vaccine for pregnant and lactating people, and use of this vaccine during pregnancy and lactation is not considered contraindicated, as it is expected to be safe.

The ACAM2000 smallpox vaccine is live and competent to replicate, which means that it can cause clinical infection and produce infectious virus that can be spread to others. This vaccine is not advised for anyone who is immunocompromised. Because the vaccine can replicate, and is contraindicated for infants under 12 months, the Advisory Committee on Immunization Practices (ACIP) considers the ACAM2000 vaccine contraindicated during lactation.

ACIP recommends pre-exposure vaccination for the following groups: persons at risk for occupational exposure to monkeypox; people who administer the ACAM2000 vaccine; people who care for patients with monkeypox; people with ongoing risk for occupational exposure to monkeypox, such as those who perform lab testing on specimens.

Regarding post-exposure vaccination, people who have had household or otherwise close contact with a person infected with monkeypox should be vaccinated ideally within 4 days of exposure. People who have had contact while wearing appropriate protective personal equipment (PPE) do not typically need post exposure vaccination.

Although the treatment of monkeypox is largely supportive (rest, fluids, pain medication, etc) there are anti-viral medications considered effective against monkeypox including Brincidofovir (oral), Tecovirimat (oral) and Cidofovir (IV).

Although there are no studies of these medications during human lactation, E-lactancia considers Cidofovir not safe during lactation because of its low protein binding, low molecular weight, and high volume of distribution. Despite being an IV medication, there is concern that premature infants and neonates could absorb the medication due to having highly permeable intestinal linings.

Brincidofovir is contraindicated during pregnancy because it is considered a teratogen based on animal studies.

According to the manufacturer, there is no data on transmission into human milk. It was found in the milk of rats, with undetectable plasma levels in nursing pups. E-lactancia considers Brincidofovir low risk. The product label indicates that there is no data to assess the presence of the medication in human milk but was found in the milk of lactating mice. The CDC states that pregnant and nursing women are not excluded from treatment with this medication.

According to a 2022 professional consensus paper from the UK, lactating individuals in high income countries are advised to not breastfeed, but rather to express their milk and discard it. They should also be isolated for 2-4 weeks until considered non-infectious. Although transmission of the virus in human milk is not known, the skin lesions are infectious, and it would be difficult to prevent viral shedding from the skin lesions into expressed milk. In low and middle income countries, the benefits of breastfeeding might outweigh the potentially increased risk of neonatal monkeypox infection.