Do Smallpox Vaccines Protect Against Monkeypox?Do Smallpox Vaccines Protect Against Monkeypox?

According to the most recent data from the Center for Disease Control and Prevention (CDC), there are more than 11,800 confirmed monkeypox cases in the United States and an estimated 36,500 infections globally. On July 23, 2022, the World Health Organization (WHO) declared the global spread of monkeypox a Public Health Emergency of International Concern โ€” its highest alert level. 

The good news: Monkeypox and smallpox are closely related, and smallpox vaccines provide some protection against the rapidly spreading monkeypox virus. Distribution of these vaccines is now rolling out to some people who are most at risk.

Infectious disease specialists Frank Esper, MD, and Ted M. Ross, PhD, break down what we know about the current vaccines available and how they can help protect against monkeypox.

Is there a monkeypox vaccine?

The crossover between monkeypox and smallpox means that the prevention plan for them also matches up. According to the CDC, smallpox vaccines are up to 85% effective in preventing monkeypox. 

โ€œThese members of the poxvirus families are so closely related that if you get immunized against any one of them, it actually protects against all the others,โ€ Dr. Esper explains. (If youโ€™re wondering, chickenpox is caused by the varicella-zoster virus โ€” despite its name, chickenpox is not a member of the pox family viruses โ€” so, if youโ€™ve had chickenpox or had the vaccine, you arenโ€™t immune to monkeypox.) 

Because we havenโ€™t vaccinated people against smallpox in 50 years, nearly half of the current U.S. population doesnโ€™t have immunity to smallpox or, by extension, monkeypox. 

โ€œTeens, 20- and 30-year-olds are probably the most susceptible population to monkeypox,โ€ Dr. Ross says. โ€œItโ€™s not surprising that youโ€™re seeing it among sexually active individuals, particularly in urban settings.โ€

Manufacturing of the original smallpox vaccine stopped in 1978. Following the September 11, 2001, terrorist attacks, however, the United States and other governments began creating vaccine stockpiles, including smallpox, due to bioterrorism concerns. That led to the production of two new smallpox vaccines, which are now being used to combat monkeypox.

When properly administered before exposure, both vaccines are able to protect against monkeypox, according to the CDC. Being vaccinated within four to 14 days of exposure to monkeypox may help prevent infection or reduce its severity.

The two types of vaccinia vaccines against smallpox and monkeypox today are the ACAM2000 vaccine and the JYNNEOS vaccine.

ACAM2000 vaccine

The ACAM2000 vaccine requires only one shot. โ€œThis is basically the vaccine that weโ€™ve had for quite some time,โ€ says Dr. Esper. โ€œItโ€™s injected into a personโ€™s shoulder and it causes an infection in that shoulder. Your immune system will then eliminate it and learn how to protect against smallpox and any other pox virus that comes around, like monkeypox.โ€ 

But higher risks come with this vaccine because the virus can replicate and spread to other parts of your body. If you get the ACAM2000 vaccine, youโ€™ll need to take precautions when caring for the vaccine site and not have close skin-to-skin contact with others. And youโ€™re only considered fully protected 28 days after the inoculation. 

ACAM2000 isnโ€™t recommended for children under the age of 1, people who are pregnant or people who are living with:

  • Heart disease.
  • Eye disease treated with topical steroids.
  • Immune deficiency disorders, including HIV
  • Atopic dermatitis (eczema) or a history of acute or exfoliative skin conditions.

JYNNEOS vaccine

The newer vaccine JYNNEOS (also known as Imvamuneยฎ or Imvanexยฎ) was licensed by the U.S. Food and Drug Administration (FDA) in 2019 for the prevention of both smallpox and monkeypox in adults. Itโ€™s considered a safer form of vaccine if youโ€™re immunocompromised or have any of the above conditions.

โ€œIt basically just goes into the skin and doesnโ€™t replicate,โ€ notes Dr. Esper. โ€œThen, your immune system learns how to protect itself from that virus. Itโ€™s similar to a flu shot.โ€

This vaccine has a lower risk of side effects. It requires two shots, spaced four weeks apart. Youโ€™re considered fully immune two weeks after your second dose. Thereโ€™s currently a limited supply of JYNNEOS, but more is expected in the next few months. The U.S. Department of Health and Human Services plans to distribute a total of more than 4 million JYNNEOS doses in 2022 and 2023.

Is monkeypox the same as smallpox?

Youโ€™re not seeing spots โ€” monkeypox and smallpox are, in fact, different. But theyโ€™re actually siblings of the same family called orthopoxvirus (or poxvirus).

The big difference? Monkeypox is far less severe and is rarely ever fatal. 

โ€œMost people infected with monkeypox will have a mild disease,โ€ Dr. Ross says. โ€œThere is probably a large pool of people who are infected and donโ€™t realize it because they have minor symptoms and only one or two skin lesions. The disease is uncomfortable but typically does not require hospitalization.โ€ Monkeypox can be more severe in children and people with compromised immune systems. 

Like smallpox, monkeypox is a virus that spreads through close skin-to-skin contact with a person who is infected who has open sores or scabs, through oral fluids or respiratory droplets. 

Smallpox is a more life-threatening disease than monkeypox, and causes pus-filled blisters to develop all over your body. The original smallpox vaccines were widely distributed in the U.S. in the 1950s, 60s and 70s. By 1972 โ€” thanks in large part to the vaccine โ€” smallpox was declared eradicated (wiped out) in the U.S., and vaccination efforts ended. Globally, smallpox was officially declared eradicated in December 1979.

Who can get the vaccine against monkeypox?

Currently, there are no plans for mass public vaccination in the United States. The two licensed vaccines available are only recommended to prevent monkeypox if you are: 

  • A laboratory worker who works closely with orthopoxviruses. 
  • In the military. 
  • Among certain qualified healthcare workers and public health responders. 

Additionally, the Department of Health and Human Services has developed a policy regarding whoโ€™ll be eligible to receive the vaccine as more doses become available. This will be based on targeting communities with the highest case rates of monkeypox and will be recommended for those with confirmed exposure. This includes:

  • People whoโ€™ve had close physical contact with someone who was diagnosed with monkeypox.
  • People who know their sexual partner was diagnosed with monkeypox.
  • Men who have sex with men whoโ€™ve recently had multiple sex partners in a venue where monkeypox is confirmed or in an area where monkeypox is spreading.

For most individuals, this means you wonโ€™t be able to go to your doctorโ€™s office to get the vaccine just yet. But if you think you may have been exposed to monkeypox, contact your healthcare provider to discuss your eligibility and vaccine availability.

โ€œIf you do worry that you might have monkeypox, we now have tests that have a quick turnaround time to get those results back,โ€ states Dr. Esper.

โ€œIf you get the vaccine within four days of your exposure, you can actually prevent the monkeypox from causing disease,โ€ he adds. โ€œOr if you get that vaccine within two weeks of exposure, you may not prevent the infection, but you actually prevent the infection from becoming severe.โ€

If I had the smallpox vaccine years ago, would I be protected?

What if you already got a smallpox vaccine years ago? You may also be wondering if a previous vaccination for smallpox could still protect you against the current outbreak of monkeypox.

The answer is that a previous vaccination against smallpox may lessen the severity of monkeypox, but thereโ€™s no guarantee.

โ€œWe donโ€™t believe that the previous vaccine will prevent you from getting the infection,โ€ says Dr. Esper. This is because even if you got the vaccine against smallpox before the 1970s, that protection may have waned over time.  

โ€œIf youโ€™ve had a previous vaccination against smallpox, you probably are less likely to get very, very sick,โ€ explains Dr. Esper. โ€œBut itโ€™s probably not enough to prevent the infection itself.โ€

How else can I protect myself from monkeypox?

In addition to getting vaccinated if youโ€™re a candidate, the CDC recommends these steps to protect yourself during the monkeypox outbreak:

  • Avoid close, skin-to-skin contact with people who have a rash that looks like monkeypox.
  • Donโ€™t touch the rash or scabs of a person who has monkeypox.
  • Donโ€™t kiss, hug, cuddle or have sex with someone who has monkeypox.
  • Donโ€™t share eating utensils or cups with a person who has monkeypox.
  • Donโ€™t handle or touch the bedding, towels or clothing of a person who has monkeypox.
  • Wash your hands often with soap and water or use an alcohol-based hand sanitizer.

While weโ€™re still learning more about the current monkeypox outbreak, past vaccines against smallpox have been found to be effective. If you believe you or a loved one may have contracted monkeypox, call your healthcare provider to find out if youโ€™re able to get vaccinated.

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