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How effective are MPX vaccines?

Vaccines will help control the monkeypox (MPX) outbreak.

The bad news is that we desperately need more doses. And we don’t know how much the vaccines help and in what manner they help (prevention, duration of disease, severity of disease).

This information is absolutely essential so people know how well they are protected and what behaviors they should (or should not) change. This information will also have major implications for controlling the outbreak worldwide.

How effective was the second generation vaccine against MPX?

The CDC website states the smallpox vaccine is 85% effective in preventing MPX among humans based on data from Africa. From what I can tell, this is based on a 1988 study in the Democratic Republic of the Congo.

Scientists looked at a pretty big sample (3,686 people) who were exposed to close contacts of MPX. Among people who were exposed and then infected, 15 were vaccinated and 54 were unvaccinated. This equates to an efficacy of 87%, which is great news! At least for the historical outbreaks.

The problem is that the virus has mutated, it’s spreading very differently than before, and it’s been a long time since people got this smallpox vaccine. So we cannot assume a smallpox vaccination from decades ago will act the same way during this outbreak.

How effective is a smallpox vaccine from decades ago?

A very recent study published in the Lancet collected data on 181 patients with an MPX infection in Spain during the current outbreak, including data on whether people had a previous smallpox vaccination. Among the 181 MPX cases, 32 (18%) had a history of the smallpox vaccination.

We cannot calculate efficacy because we don’t know how many people were exposed and not infected, but overall this was not great news. We need to better understand the protection provided in the context of the current outbreak, like investigating the duration of protection and why vaccine effectiveness may have changed.

How effective is Jyennos?

We have more than 22 clinical trials of Jyennos… against smallpox. This means we know it’s safe, but we don’t know how effective it is against MPX. A few years ago, the FDA approved the vaccine for monkeypox by relying on survival data from primate studies. (Far more primates survived after vaccination compared to those without vaccination.)

But this is really all we have to go on for the current vaccine rollout.

Scientists are smartly collecting data during the rollout, though.

For example, a French preprint study followed 276 people who received a shot after a high-risk contact. Ten people developed MPX quickly thereafter (which is not surprising as vaccines need time to be effective). But two people were infected at 22 and 25 days after vaccination, which was unexpected.

This means that the vaccine is not perfect at preventing infection after close contact. We certainly need more data.

We hypothesize that even among those who get vaccinated and infected, the vaccines still help reduce viral load and, thus, severity of infection.

We have yet to see the clinical data on that yet, though.

How effective are other innovative strategies?

Because of suboptimal vaccine supply in the U.S., we are forced to think innovatively about how to broaden the vaccine reach during this public health emergency. As a result, we are trying two methods, but they leave us with even more questions:

1. Intradermal vaccination. 
2. Earlier this week, the FDA authorized intradermal vaccination, which means administering the vaccine at the top layer of our skin. The skin is home to a number of immune cells that trigger a potentially better immune response and requires less vaccine liquid (we could get five vaccines with this new strategy compared to one with the intramuscular route). This strategy has been used in other emergencies, like Ebola. But we only have one study showing this works for the smallpox vaccine. In 2015, scientists randomized 524 people to test vaccination using this method and showed it was effective. When we use this method with other vaccines (flu and rabies), there is also significant skin irritation. We don’t know if that will be the case with this vaccine. Implementation is also going to be difficult, as it requires special training and confidence. How much will this impact effectiveness or uptake? We don’t know.
3. Dosage sparing. Some jurisdictions, like New York, are also spacing the dosing. So, people get the first dose (the regular intramuscular route) and then have to wait until we get more vaccines in the fall for the second dose. This increases reach, but the protection after one dose is unknown.

Given the (limited) evidence, vaccine shortage, and urgency of this emergency, I support these approaches, as long as people understand that this is experimental and we collect data along the way to make better, data-driven decisions in the future.

Bottom line

We really need real-world effectiveness studies on MPX vaccines. This will be coming. In the meantime, we have to make difficult policy decisions based on limited data. (Sound familiar?) But we cannot repeat our COVID-19 mistakes and provide a false sense of security with vaccines. Communication around scientific uncertainty and how it’s being used to make decisions needs to be at the forefront so we can build trust and effectively dampen the outbreak across the globe.

Love, YLE

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“Your Local Epidemiologist (YLE)” is written by Dr. Katelyn Jetelina, MPH PhD—an epidemiologist, biostatistician, wife, and mom of two little girls. During the day she works at a nonpartisan health policy think tank, and at night she writes this newsletter. Her main goal is to “translate” the ever-evolving public health science so that people will be well equipped to make evidence-based decisions. This newsletter is free thanks to the generous support of fellow YLE community members. To support the effort, please subscribe here:

By Dr. Katelyn Jetelina.

Your Local Epidemiologist. August 10, 2022. Reprinted with permission.

School is starting. And, with it, the contentious debate on what schools should and should not do. While the pandemic ravages on, the landscape continues to morph, and because of that, every subsequent school year has looked very different (hopefully for the better).

Unfortunately, student absences continue. As seen in London, (BELOW) students’ absences continue to be higher than before the pandemic. They were especially high at the end of this school year when BA.5 took hold. (Editor’s note: this was true of the White Plains City School District, too).

We know this is partially driven by reinfections, as children have the highest reinfection rate compared to any other age group.

(Source Kit Yates)

It’s imperative that schools remain open, but they continue to seem stuck between “do everything” and “do nothing.” 

How many layers can a school feasibly implement given pandemic fatigue, limited resources, strong opinions, and differing risk calibrations?

The answer is multi-level; it requires a balance of tradeoffs from students, parents, teachers, schools, and the community. Our primary goal should be to maximize the number of days children are present. This can be accomplished many ways, but I think there are three buckets schools should really focus on.

Back-to-school vaccination campaign

We need strong, universal vaccine campaigns at schools.

Parents report that schools, pediatricians, and health departments are the most trusted sources of information about vaccines. Schools can also significantly improve access to vaccines, as 38% of parents say they do not have enough info on where their kid can get vaccinated. A fall back-to-school campaign could really help move the needle for vaccinations, and thus school absences. And not just for COVID, but other vaccine preventable diseases.

• COVID-19: The number of children vaccinated against COVID-19 remains abysmally low. (Only 10% of 5-11 year olds and 27% of 12-17 years olds are up to date.) Vaccines are safe, they prevent infections (especially within a few months of vaccination), prevent severe disease, and reduce risk of long COVID. But parents have a lot of great questions; we need to anticipate concerns.
• Flu. The flu season in Australia just wrapped up, and it wasn’t pretty.This is notable because, historically, Southern Hemisphere patterns predict what is to come in the Northern hemisphere. (We’ve been worried about a “twin-demic” since COVID-19 began, but it hasn’t happened yet. We are not sure why.) We should heed Australia’s warning and prepare for the worst.

• Other routine vaccines. New York is strongly warning parents about a dip in routine vaccinations. For example, 13.8% of children have not been vaccinated against polio. This reflects patterns we’ve seen nationally and internationally with other routine vaccinations, too. We cannot lose decades-long progress towards eliminating vaccine-preventable diseases.

We can reimagine how vaccines and information reach students and parents.

For example, the Teens for Vaccines campaign in Detroit was highly successful by empowering student ambassadors.

A school district in Florida recognized that active communication and education promoted vaccine confidence and uptake, so they sent text reminders, posted on social media, and provided credible information. Los Angeles School District even had a TikTok campaign.

Ventilation and filtration

Schools need to upgrade their ventilation and filtration systems.

This is one of the most powerful tools we have to curb COVID-19 and other viruses because it happens in the background—it’s an institutional-level intervention that doesn’t require the teachers, parents, or students to do anything. Unfortunately, a small proportion of schools report using these strategies, especially in rural and mid-poverty schools. Many administrators aren’t aware that federal funding is available for ventilation improvements.

Layman wording on how to improve ventilation and filtration is difficult to find. I worked with Dr. Whitney Robinson and Katie Harper, fellow epidemiologists, on a one pager that outlines available strategies and how to test effectiveness. This may help.

Testing and isolating

Now that everyone is eligible for vaccines, and treatments (monoclonal antibodies, antivirals and Evusheild) are available for high risk family members, a more targeted approach to testing, isolating, and masking in the upcoming school year is reasonable:

• Testing. Sick, symptomatic kids should stay home. At-home or at-school antigen tests would be a great tool to use for this. (Do not use PCR tests, as these could stay positive for weeks).
• Quarantining. Attending school far outweighs benefits of quarantining for a respiratory virus that is out of control in the community. It’s reasonable (and overdue) to remove quarantine requirements.
• Isolation. The ideal scenario is that a child tests-to-exit isolation using antigen tests. But this can mean a lot of school missed (and a lot of work missed for parents), with the average infection lasting 8-10 days.
• The CDC says people can leave isolation after 5 days if they remain positive as long as they mask. If children need to go back to school at that time, it’s certainly reasonable and should be expected that kids mask if they are still positive.
• Masks.
• Masks are effective to the wearer. They are even more effective if everyone is masking.
• If a school is in an area of high transmission, it’s certainly reasonable to mask to reduce transmission and, thus, reduce missing school.
• However, for that strategy to work, the wearer must mask everywhere else in the community. I don’t think it makes sense for a school to mandate masks if the larger community does not do so either. We shouldn’t ask students to hold down the fort if the larger community hasn’t also committed either.

Other random thoughts

Preparedness needs to be the name of the game. Schools need a plan in case we do get another Omicron-like event or if there’s is a big superspreader event, like a homecoming dance.

There need to be very important conversations about normalizing decisions around masking, even if not required. Very important conversations may also need to ensue if a child is high risk in a classroom, so they, too, can attend in person learning.

Bottom line

This pandemic landscape continues to change and, with it, we should adapt. But if we continue to fail to act, children will continue to have their education disrupted by COVID19. There are a number of measures schools can put in place to maximize the number of days children are in school so they can have a safe and successful school year.