Does one-fifth of a monkeypox vaccine dose provide enough protection against the virus?

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As demand for the monkeypox vaccine continues to grow and supply begins to diminish, the Biden administration took steps this week to change how much each individual receives.

Vaccines administered to reduce monkeypox infections will now be given in a smaller dose in order to stretch the current supply of dosages, the Associated Press reported.

The new plan announced by the The Food and Drug Administration will authorize a dose that is one-fifth the normal dosage. The measures were taken in response to the rapid spread of the virus, according to the agency.

Furthermore, the JYNNEOS vaccine -- used to prevent contraction of smallpox and is authorized to be used against monkeypox as well -- will now be administered between layers of skin, the FDA said. This is known as an intradermal injection. In any other circumstance, the monkeypox vaccine would be injected into layers of fat.

Health officials say the practice may have a better impact on the immune system, CBS reported. Those who receive the vaccine under the new guidance will still get two shots four weeks apart.

An estimated 1.6 million people in the United States are considered “high risk” for contracting the virus, NPR reports. The vast number of people is compared to a smaller 1.1 million – the number of doses that are available. The new strategy is estimated by federal officials to increase the stock of available vaccines five-fold.

How effective will the vaccine be under the new provision?

According to Robery Fenton, the White House monkeypox response coordinator, the plan will not have a negative impact on safety or effectiveness of the vaccine.

“It’s safe, it’s effective, and it will significantly scale the volume of vaccine doses available for communities across the country,” Fenton said in a news conference with CDC and public health officials. “We encourage jurisdictions to utilize the alternative dosing method as quickly as possible, and we’ll be your partner in this step every step of the way.”

The FDA also highlighted a 2015 clinical study by the National Institutes of Health that suggested one-fifth of the Modified vaccinia Ankara (MVA), or smallpox and monkeypox vaccine, isn’t that much less effective than a full dose. The data showed that approximately 94% of those who received the smaller dose had enough antibodies to fight the virus compared to 98% of those who received a full dose.

The FDA says that the JYNNEOS and ACAM2000 vaccines are both effective in combating both smallpox and monkeypox. However, data has not yet been published to show how well ACAM2000 protects against the current monkeypox virus, according to the CDC.

The Biden administration is still moving forward with the plan in hopes that the new strategy will make a substantial impact on containment efforts.

“This is a significant priority of not only the President, but this administration, to make sure that we’re working across all of the government and with all communities to make a whole-of-government process here to make sure that we work as quick as possible to control and contain (monkeypox) in the United States,” Fenton said.