FULL CLAIM: "I don't know who needs to hear this but Polio and smallpox never reached natural herd immunity, they were eradicated by vaccines"
REVIEW
In early December 2024, social media posts sharing a meme claiming that “Polio and smallpox never reached natural herd immunity” and that these diseases were “eradicated by vaccines” went viral on Facebook. Among posts which received significant engagement were those from the Facebook pages The Other 98%, which has 7.1 million followers, and The Resistance, which has 383,000 followers. The former received more than 45,000 user engagements and 17,000 shares.
Given the popularity of these posts, we decided to examine the veracity of the claims made in the meme. Along the way, we also discuss the impact that vaccines have had on vaccine-preventable diseases in general.
Infection never managed to establish herd immunity against smallpox and polio
Herd immunity occurs when a community is protected from an infectious disease because a sufficient proportion of the community is immune to a disease. Virologist Angela Rasmussen wrote the following in a commentary for the journal Med:
“Herd immunity is based on our understanding of viral pathogens as obligate intracellular parasites that require a host for replication. If enough people are immune to infection, then the virus cannot be transmitted to new susceptible hosts and will be eliminated from circulation within the population. When a sufficient proportion of the population are immune and thus thwart the pathogen’s ability to circulate, that population has reached the herd immunity threshold.”
Immunity can be acquired through infection, as well as through vaccination. Unlike vaccination, acquiring immunity through infection involves exposing oneself to the risks of disease, including disability and death.
Smallpox can be deadly. The U.S. Centers for Disease Control and Prevention (CDC) states that “the case-fatality rate differed for the different clinical forms, but it was approximately 30% overall in unvaccinated individuals”. In rare cases, the infection can also lead to blindness.
As for polio, between 1 in 50 and 1 in 500 infections result in paralysis in unvaccinated people. Polio can kill if the paralysis caused by the infection affects the muscles needed for breathing. The invention of the iron lung in the late 1920s did reduce polio deaths caused by suffocation, but it couldn’t cure the paralysis. While most patients only needed the iron lung for a few weeks, the rest were permanently affected by paralysis and would have to spend the rest of their lives in the iron lung.
Smallpox and polio have existed for thousands of years. Smallpox-like rashes have been found on Egyptian mummies and early descriptions of a disease resembling smallpox can be traced back to the 4th century CE. Artwork from Ancient Egypt suggests that polio has existed for thousands of years, and polio was documented in the written record in the 18th and 19th centuries.
But the eradication of both diseases has only been achieved relatively recently. Smallpox was officially globally eradicated in 1980. Polio eradication has been achieved in most places, though not on a global scale. The European Region was declared polio-free by the World Health Organization only in 2002. Polio was eradicated in the U.S. in 1979. But the disease remains endemic in Afghanistan and Pakistan.
This underscores the fact that infection-induced immunity—also called natural immunity—never managed to bring about herd immunity sufficient to eradicate both diseases from a community. The eradication of both diseases only occurred after vaccines became available.
Vaccines’ role demonstrated by reemergence of vaccine-preventable diseases in areas of reduced vaccine coverage
Some argue that advances in sanitation and nutrition eradicated vaccine-preventable diseases like polio, not vaccines. While improvements in sanitation and nutrition significantly reduced the spread of infectious diseases, they’re insufficient in themselves to keep infectious diseases at bay.
This is illustrated by relatively recent reappearances of vaccine-preventable diseases in developed countries, which presumably meet adequate sanitation and nutrition standards. These outbreaks also tend to specifically affect pockets of a community that’s underimmunized.
For example, a measles outbreak occurred in New York between 2018 and 2019.
It primarily affected Orthodox Jewish communities in Williamsburg, a neighbourhood in Brooklyn, and neighbouring Rockland County.
More than 600 cases were reported in New York City, with 72% of these cases in Williamsburg, while more than 200 were reported in Rockland County[1]. The proportion of children who received at least one dose of measles vaccine in Williamsburg, where the majority of cases in New York City were reported, was 79.5%[2]. Coverage in Rockland County schools that were affected by the outbreak was estimated at just 77%[1,2]. Both were well below the 95% coverage (two doses of vaccine) required for achieving herd immunity.
The New York outbreak nearly saw the U.S. losing its measles elimination status.
France also saw a measles outbreak from 2008 to 2011, with the most affected areas also being the ones with the lowest vaccine coverage. One study noted that there were more than 22,000 reported cases[3]. Nearly 5,000 people were hospitalized; more than 1,000 hospitalizations were for severe pneumonia, and 27 for encephalitis/myelitis. Ten people died.
There was also a measles outbreak in Wales between 2012 and 2013, linked to historically low vaccine coverage in the community. More than 600 cases were reported.
Another example is pertussis. From the CDC:
“Three countries – Great Britain, Sweden, and Japan – cut back the use of pertussis vaccine because of fear about the vaccine. The effect was dramatic and immediate. In Great Britain, a drop in pertussis vaccination in 1974 was followed by an epidemic of more than 100,000 cases of pertussis and 36 deaths by 1978. In Japan, around the same time, a drop in vaccination rates from 70% to 20%-40% led to a jump in pertussis from 393 cases and no deaths in 1974 to 13,000 cases and 41 deaths in 1979. In Sweden, the annual incidence rate of pertussis per 100,000 children 0-6 years of age increased from 700 cases in 1981 to 3,200 in 1985.”
These experiences demonstrate “that not only would diseases not be disappearing without vaccines, but if we were to stop vaccinating, they would come back”, the CDC states.
REFERENCES
- 1 – McDonald et al. (2019) Notes from the Field: Measles Outbreaks from Imported Cases in Orthodox Jewish Communities — New York and New Jersey, 2018–2019. Morbidity and Mortality Weekly Report.
- 2 – Zucker et al. (2020) Consequences of Undervaccination — Measles Outbreak, New York City, 2018–2019. New England Journal of Medicine.
- 3 – Antona et al. (2013) Measles Elimination Efforts and 2008–2011 Outbreak, France. Emerging Infectious Diseases.
