Monkeypox and Herd Immunity

In 1980, smallpox was declared eradicated following an intensive global vaccination campaign.  The virus, Variola, has some close relatives that can infect humans, one of which is monkeypox.  Monkeypox isnt nearly the problem that smallpox was; it has a much lower mortality rate and outbreaks tend to fizzle out quickly due to poor human-to-human transmission.

However, a recent paper suggests that monkeypox infections are becoming an increasing problem.  So why is it emerging now?  Its a problem we’ve been anticipating, actually.  Turns out that when you get the smallpox vaccine (or smallpox itself), it also protects you from monkeypox.  So pre-eradication, most people were immune to monkeypox.  If you met up with an infected animal, chances are you were immune and wouldn’t get infected.  If you did somehow get infected, chances are most people around you were immune so you couldn’t transmit it to others.  An immune host is not fertile ground for viral replication, so whenever immune hosts are encountered, the chain of viral transmission ends.  In fact, a highly vaccinated population helps those few individuals that are not vaccinated by greatly limiting the potential of the virus reaching the unvaccinated (“naive”) individual.  Thats called herd immunity.

Turns out herd immunity to smallpox, and therefore monkeypox, is waning.  Vaccinations stopped in 1980 so anyone born after that is naive and therefore there is a major lapse in herd immunity.  Risk of infection with monkeypox virus is now as much as 20 times greater than 30 years ago.  Interestingly, all those old people born before 1980 who were vaccinated have a much lower risk of infection, telling us that immunity from vaccination lasts 30+ years.

So why should we worry about waning herd immunity to a rare and relatively mild disease that is hardly contagious?  Well, variola and monkeypoxviruses are about 96% identical.  We dont know how much  monkeypox needs to mutate to become sustainable in humans or more virulent.


20 thoughts on “Monkeypox and Herd Immunity”

  1. This is in reply to several comments. First, as I mentioned in another reply, the side effects of vaccination include a 1 in 3 million chance of dying. This was pre-AIDS and other recognized contra-indications so if we were to blindly vaccinate the whole population of the US the death rate from vaccination would likely be significantly higher that what we have seen before. With a growing “anti-vax” community, I would think a decision to vaccinate the US population would go over horribly. Keeping an eye on localized outbreaks in the DRC, perhaps vaccinating individuals there (who can safely take the vaccine) may be sufficient to limit dissemination.
    Sarah is right that a disease outbreak in a remote part of the world can fairly easily spread to another part of the globe. However in the case of monkeypox (and smallpox) we have the advantage that vaccination is effective post-exposure, which means that if you get infected you can get vaccinated after, and still be protected (within a limited time frame of course). This was key in eradicating smallpox because you could vaccinate all people who came in contact with a sick individual and even if they were already infected, you could break transmission. We could do the same thing with monkeypox. Most vaccines are not effective post-exposure.
    Another comment said that we could eradicate a mutant monkeypox just like we did smallpox. But thats probably not true. There is a key difference between the life cycles of these viruses and that is the host range. Variola was limited to humans. So you vaccinate all the humans and the disease is gone. Monkeypox is in all kinds of animals so it can go back and forth between humans ans animals. We probably couldnt eradicate it from diverse animal populations.

  2. The thought of vaccinating over 307 million Americans due to the slight chance of a monkeypox-turn-smallpox mutation seems ridiculous. First note that the paper cited is about a major increase in human monkeypox incidents in the DEMOCRATIC REPUBLIC OF CONGO. The incidence rate in the participating health zones of this third-world country, between November 2005 and November 2007, was only 5.53 cases per 10,000 people. Now with such a low incidence rate and human-human transmission rate, is it really necessary to vaccinate millions of people in a first-world country, thousands of miles away, for fear of a monkeypox or smallpox outbreak? Sarah’s article definitely brings up a good point– that African rodents brought to America as pets could be carriers of the disease. The article also mentions, however, that the possibility of a monkeypox pandemic is very slim because the virus weakens as it passes from human to human. Knowing all this, we can understand that among the few human subjects monkeypox does happen to infect, the chance of a successful viral mutation from monkeypox to smallpox is negligible. For those still fear- mongered by the Democratic Republic of Congo study, perhaps taking alternative measures, such as tightening customs and enforcing stricter trading laws, might mitigate worries of a future pandemic.

  3. It is quite scary to think that due to the younger generation’s lack of vaccination against smallpox, we are more vulnerable to getting monkeypox. When I think of how much people are in contact with one another and how much people travel through cars, buses and planes, it’s no wonder the risk of infection of monkeypox is “20 times greater than 30 years ago”. Viruses can spread so easily from person to person through our modes of transportation, which makes our lack of herd immunity all the more terrifying. Further, I think we also need to worry about the spread of monkeypox in other countries. In one CNN article ( it said that the monkeypox virus was spread to the U.S. seven years ago when a few African rodents were brought in as pets. In addition to vaccinating Americans, we should take care to both monitor and try to suppress the spread of the virus around the world.

  4. After reading such a frightening report about the possible outbreak of a deadly virus, it’s obvious that everyone’s natural response is that we would “rather be safe than sorry” and start giving out smallpox or a new monkeypox vaccinations to prevent a possible outbreak. After thinking this through a bit more, though, I realized that being “safe” in this way (by being precautious) would probably do more harm than good. Besides the obvious risk of the side effects and possible death the vaccine itself could produce, the cost of reproducing this vaccine without a significant threat at the moment would not be worth it. If the money involved seems like a cold thing to factor in when lives are at stake, there is also the fact that putting a vaccine back on the market for a virus that is supposed to be eradicated would definitely make the news and would cause unnecessary hysteria when no real health threat currently exists… only a possible one. Hospitals do not need people rushing in saying that they think they might have smallpox or monkeypox after they hear something on the news and simply become panicked when there are real threats doctors and nurses must actually deal with. The worry that such a revival of the vaccination would cause may do more harm than good. As Alex said, there are many possible health risks just waiting to occur, and it is not worth it to have everyone worrying about what could possibly happen. This is not to say that we shouldn’t keep an eye on possibly dangerous diseases, but there is no need to issue worldwide vaccination movements and health warnings if there is no real threat on the rise just yet. In fact, it would be careless and unnecessary to do so.

  5. Even though monkeypox isn’t much of a threat at this moment, who knows how dangerous it will be ten years from now. As many people on this post have stated, it’s better to be safe than sorry. Also, it would be vastly easier to distribute vaccinations now than it was 30 years ago. People are cautious. And they’re willing to cooperate, as evidenced by the public’s quickness to combat the H1N1 virus. If we managed to eradicate a virus in the 80’s, we can certainly eradicate a similar virus now. So I think the medical and science community should make an effort to eliminate this problem before it gets any worse, which it inevitably will, given that the monkeypox virus is nearly identical to the smallpox virus and that viruses mutate with little trouble. We must regain herd immunity if we want to protect the global community.

  6. One thing I found very interesting about this post is the fact that a vaccine can remain effective for over 30 years. One would think that since the smallpox vaccine was so helpful, and the disease so deadly, it would continue to be given out. However, the fact that it was so helpful was the reason the vaccine stopped being given. However, it is obviously too late to help this now. In response to Cydni’s comment, I agree that the decision to give out new vaccinations should depend on the rate at which people are being infected by monkeypox and the risks that this disease is posing for the immediate future. Although, the odds of being harmed by the vaccine don’t seem to be very high, there is enough danger where we must take precautionary steps to protect ourselves from this new virus. However, it is scary to think that it is only a matter of time before monkeypox becomes easily spread through humans and poses a problem similar to that of smallpox almost 30 years ago.

  7. Monkeypox and variola are both members of the family Orthopoxviridae. The orthopoxviruses are traditionally classified together because they are immunologically cross-protective. Meaning that if you vaccinate (or are infected by) one orthopoxvirus, you become immune to all of them. This is why we can use vaccinia virus or cowpox virus to immunize against variola, or monkeypox. So a monkeypox specific vaccine would also protect against smallpox, although hopefully we will never have to worry about smallpox coming back.

  8. The virus wouldn’t mutate into Variola, the smallpox virus, but rather become a human-adapted strain on Monkeypox. There are already several different strains and they differ in their pathogenesis and mortality rate. No matter how deadly or transmissible it becomes, it will always be considered monkeypox. Presumably, the smallpox vaccine would still work against that strain.

  9. Like Estello said, my initial thoughts upon reading this article have shifted as a result of reading the comments. If monkeypox were to mutate, would it definitely mutate into smallpox, or are there many other plausible mutations? In the past, even if we have immunity to a virus (for example, influenza), the immunity has not stopped the virus from infecting humans and causing near-hysteria. So if monkeypox were to mutate into anything besides smallpox, wouldn’t the epidemic be inevitable? If so, the chances that immunizing against smallpox would help prevent an outbreak seem quite small, and therefore not worth the risk.

  10. I understand that it’s probably desirable for monkeypox viruses to mutate into smallpox viruses so that it can spread faster. But if for some reason, maybe because of the high risk, scientists decided to develop a vaccine for monkeypox that is less risky, would that new vaccine immunize us to smallpox also?

  11. Honestly, while reading this post, I thought to myself, “Well that sucks,” but reading through the comments, I’ve come to the conclusion that vaccinating people all over again would be too risky, especially seeing that there hasn’t been a major outbreak.
    I’ve seen that more often than not, people tend to get themselves vaccinated only if it plays an immediate role to their health. So, as terrible as it sounds, I guess the only way for people to really start taking this waning herd immunity to heart is if it is visibly seen as an immediate hazard.

  12. Transmission is typically from animal to human. Despite its name, the virus seems to be transmitted from rodents. It could be from bites or eating or preparing an infected animal, Im not sure. People living in and close to forested areas are more prone to infection because of their increased contact with the animals.
    Careful monitoring is certainly key to controlling emerging diseases. Although it seems like the response to the Swine flu was slow, in fact it was extremely rapid, its just that the technique for making the vaccine is time consuming. The epidemic virus was isolated, identified and fully sequenced within days of noting an unusual pattern of influenza-like illness. Making sufficient vaccine then takes about 6 months, hence the apparently slow response.

  13. Although monkeypox isn’t as contagious or dangerous as smallpox, the fact that it is 96% identical to each other is exactly why we should worry about the withering herd immunity to it. It won’t be long before monkeypox reproduces and mutates itself through means of natural selection to possibly become as effective of a virus as small pox. But the fact that the vaccine has such risky side affects complicates things on a whole different level. I guess the decision to vaccinate should depend on the mortality rate of the infection and the rate at which people are being infected. What are the rates for death from monkeypox. Because im not sure if a vaccine that kills 1 in 3 million is that much greater odds.

  14. So can the monkeypox virus be transmitted from animal to human, or is it only in rare cases with close contact with an infected animal? Because this seems similar to bird flu, which has very poor transmission from animal to human. Scientists are worried that if that virus mutates it could easily cause a deadly, global pandemic. The only way to be safe is to keep an eye on suspected virus outbreaks, and to develop a vaccine, if possible. The swine flu outbreak this past year really showed the gaps in an epidemic prevention system. Scientists were clearly caught off guard, and several months passed before a vaccine became available. A better safe than sorry mentality could save many lives.

  15. Trevor asks why we dont continue vaccinating in preparation for a monkeypox outbreak. The issue is one of risk vs benefit. The vaccine has some serious side effects, including death in about 1 in 3 million people. Immunosuppressed people are especially at risk, and with high rates of HIV in Africa, there is a significant proportion of the population that could not be vaccinated. The risk of serious side effects were acceptable in the face of variola, but most people would not take the risk now.

  16. Not that the possibility of a monkeypox outbreak doesn’t raise some unsettling concerns about herd immunity, but isn’t this just one of many modern health concerns? Though recent outbreaks of novel influenza strains have relatively contained, there are any number of widespread diseases that could suddenly mutate to disastrous results. Tuberculosis is one example, whose latent form incubates in a staggeringly high percentage of people. Despite the threat of previously weak viruses, I would say that we have other concerns. On a side note, isn’t the structure of the plague readily available online?

  17. I fully support the “better safe than sorry” mentality as well. I don’t think smallpox should be considered eradicated if there is such a similar viral strain still infecting humans. Addressing the problem now, by enforcing vaccinations, will save countless lives as well as money that would be needed to develop vaccines for mutated monkeypox viruses.

  18. I find this post very frightening and believe that in this case, we should worry about waning herd immunity. This is because if vaccinations stopped in 1980 that means there must be millions of people who are “naive”, as stated in the post. Furthermore such young populations (people under the age of 30) tend to interact a lot more with each other than they do with older populations. Also, the new generation (of children or babies) is apparently naive too. Therefore, if monkeypox mutates, which most viruses are very likely to do, then its newly advantageous or better suited form for infection to humans, will infect a naive person who in turn would have the potential to easily infect many of the other naive people and before we know it there would be an epidemic raging out of control.

    From what we have learnt so far in class, viruses have a horrible history and reputation of easily eradicating huge populations. “Better safe than sorry”. Since we know about the monkeypox virus and in fact have at hand the ability to produce smallpox vaccines which are effective against monkeypox, there should be renewed awareness and vaccination campaigns to prevent smallpox, monkeypox or any other related virus.

  19. I have often wondered why we don’t just continue on giving out the smallpox vaccination. I know it is “basically eradicated” but I always believed in covering my bases and this paper proves that. If monkeypox did eventually mutate at any point in time, it could become very deadly and it could herald in a new smallpox epidemic. With the herd immunity dying out, I believe that this is a big sign that we should start up smallpox vaccinations again, if only to prevent a terrible future epidemic from happening or to lessen the blow it could deal.

  20. The idea that “We dont know how much monkeypox needs to mutate to become sustainable in humans or more virulent” is a frightening notion. The virus inevitably will mutate and become more effective at spreading and infecting, and all we can do is sit back and wait for evolution to do its damage. Its unnerving to think that at any minute a monkeypox virion might suddenly gain the ability to penetrate skin or travel from human to human, and with our herd immunity dying out, we are left defenseless.

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