The Omicron variant surge being observed in different parts of the world at the end of 2021 and beginning of 2022 is confusing the public because so many of those who are being diagnosed as infected were partially or fully vaccinated. Vaccines are not a magical forcefield that prevents a virus from landing on a person and beginning an infection. What vaccines do is give the body’s immune system advanced warning of what a virus (or bacteria) looks like. Armed with that information, the immune system is ready to clear out the virus as soon as possible, often preventing infection. And, if the infection is underway, the infection can be halted ahead of any significant symptoms.
This is why those who are vaccinated are exhibiting less serious symptoms than those who are not when it comes to the novel coronavirus infection, COVID-19. Of course, no vaccine is 100% effective, so there will be those who do not mount a significant immune response and can still be severely affected by an infection. At a population level, well-vaccinated people are less likely to be infected, or to show symptoms if they are infected. This is why the novel coronavirus is forecast to become endemic, a nuisance virus like all the other viruses that cause cold and flu-like symptoms. From a public health perspective, it would be better for everyone to achieve that immunity artificially through vaccination because the risk of a vaccine adverse event is significantly lower than the risk of complications from a natural infection.
This concept of infection-with-immunity is not new. Ever since Edward Jenner developed the smallpox vaccine back in the late 1700s, observant clinicians and scientists have noticed a stark difference in the presentation of vaccine-preventable diseases between the vaccinated and the unvaccinated. They noticed that unvaccinated and non-immune (from previous infection) people have a much higher risk of severe disease. On the other hand, vaccinated and/or immune people can still show some signs of the disease, but they are not as severe as the full-blown disease would be on average. Even with these cases of modified or non-severe smallpox, the disease was declared eradicated in 1980.
In 1901, Dr. Allan Warner of the Isolation Hospital at Leicester, England, took a series of photographs of patients with smallpox. One of those photographs has become quite well-known, and we have a digital copy of it in the Historical Medical Library at the College of Physicians of Philadelphia:
The two boys are said to be 13 year-olds and infected with smallpox at the same time during an epidemic of the disease in the United Kingdom. (One of the last big ones there.) The boy on the left is showing a full-blown presentation of smallpox, with the pus-filled pustules all over his body, concentrated on his face and arms. (Unlike chickenpox, which concentrates on the body and less on the face and extremities.) The boy on the right is at the hospital in the same isolation unit because he also is showing some pustules (and perhaps a slight fever or malaise), though certainly not as many. Yes, one could argue that this picture shows a point in time, and the child on the right could have gone on to develop more severe disease, but he did not. In fact, the pustules on the boy on the right have already gone through the process of scabbing and beginning to fall off, leaving him unscarred. This is noted in the book where pictures like this were published. (You can see and read the full book in the Wellcome Collection online.)
Another image that is also at the Historical Medical Library at the College of Physicians of Philadelphia is this one, showing three children also at a smallpox isolation ward:
You can’t see them clearly, but the two children on either side had been vaccinated in infancy, and they showed only a few pustules here and there. The infant in the middle was not vaccinated, and he was covered in the pustules. After the pustules scab over and fall, the disfigurement to the skin is often lifelong, if the child survives. Mortality from smallpox was as low as 1% and as high as 30-50% depending on the strain and the availability of medical care. People with smallpox could also succumb to bacterial infections on the skin, pneumonia from the virus in their lungs, or brain damage from the fevers or the virus reaching their brain. There was also a hemorrhagic form of the disease that is almost 100% fatal.
Another picture that I recently came across was this one, digitally stored on the Historical Medical Library servers:
The writing under the image reads, on the left: “‘Pig’ Robinson, Never Vaccinated, Confluent Smallpox.” On the right: “Wm (William) Butler. Vaccinated 5 years of age. Moderate take. Mild smallpox.” The “moderate take” is talking about the smallpox vaccine and how much of a mark it made on the person receiving it. If it did not leave a mark, it is believed that the vaccine did not take, and people were often given another dose. As you can see, these two men look just like the children above. The vaccinated person with a few pustules while the unvaccinated person is covered in them. (And Mr. Robinson above shows some facial swelling, too.) The picture was taken in Virginia in 1904.
Do these pictures show that the vaccine caused only a mild illness and not fully protected people from infection? No, not at all. Remember that these pictures were taken at smallpox isolation hospitals. As a result, anyone showing even a hint of a pustule were taken to those centers for isolation. For the most part, vaccinated people showed no signs or symptoms of the infection because it was cleared before any sign showed up. And we now know that the vaccine conferred infection for quite a long time for most — not all, but still the grand majority of — people.
Similarly, today we have situations in which children vaccinated against measles develop measles. Or people vaccinated for influenza get influenza. But it is all about the proportions and the outcomes. Most people will not get the diseases for which they’ve been vaccinated. If they do, it is usually a milder course of the disease. Of course, these are not absolutes. Some vaccinated do get the full-blown illness, and some unvaccinated have mild disease. But, as my biostatistics professor was fond of saying, “on the average and in the long run” vaccinated means less disease and the end of outbreaks and epidemics.