Achieving herd immunity with safe and effective vaccines reduces disease and saves lives. For SARS-CoV-2, herd immunity should not have been considered a threshold for elimination. Instead, it should have helped us understand that if immunity built up in the population, whether through infection or vaccination, the epidemic would recede before everyone was infected. Since we have not been able to stop all infections, the policy should have focused on minimizing exposure to those who are already known to be significantly more exposed to serious illness, while limiting the damage caused by prolonged restrictions. In a JAMA 2020 patient page on herd immunity, Dr. Angel Desai, associate editor of JAMA Network Open, and Dr. Maimuna Majumder of Boston Children`s Hospital, Harvard Medical School, also explain that herd immunity can be achieved through natural infection and recovery:5 An unfortunate result of this pandemic period was that herd immunity was widely understood to refer only to an elimination threshold reached by vaccination. Close to this goal, it was deemed dangerously inappropriate. Two weeks after the Great Barrington Declaration was released, Nature reported on the “false promise of herd immunity” against Covid-19. One virologist wrote that “herd immunity has never been achieved by naturally acquired infections.” In a shocking reversal that looks like a redefinition of reality, the World Health Organization has changed its definition of herd immunity.
Herd immunity occurs when enough people acquire immunity to an infectious disease so that it can no longer spread widely in the community. In 1971, we discussed herd immunity and its relevance to vaccination practices (1), using applications from Reed Frost`s epidemic model (2) and a stochastic simulation model for a family community (3) to illustrate basic concepts. This presentation builds heavily on our previous discussion*, but will also explore how these herd immunity concepts relate to some important current immunization issues. Herd immunity depends on the risk of infection of the disease. Diseases that spread easily, such as measles, require more immunized people in a community to achieve herd immunity. Herd immunity protects the most vulnerable members of our population. When enough people are vaccinated against dangerous diseases, those who are susceptible and unable to get vaccinated are protected because the germ cannot “find” these susceptible people. Herd immunity (also called community immunity) protects people who are not immune to a disease, such as those who: Following the concept of pathogens to which we have sterilizing immunity, such statements were misleading. When experts – and the public – began to realise that neither a previous infection nor vaccination would lead to lasting immunity to SARS-CoV-2 infection, many became pessimistic about the possibility of herd immunity and the term was again considered irrelevant to Covid-19. Herd immunity has always been our greatest asset in protecting the vulnerable, but public health has failed to use it wisely. The post generated nearly 27,000 likes in less than a week.
Other social media users shared false claims that Merriam-Webster changed the definition of “anti-vaxxer,” PolitiFact reported. In March 2020, shortly after Covid-19 was declared a global health emergency, leading experts predicted that the pandemic would eventually end thanks to herd immunity. Infectious disease epidemiologist Michael Osterholm, who has advised President Biden, said in the Washington Post that even without a vaccine, SARS-CoV-2, the virus that causes Covid-19, would eventually “run out if the spread of infection conferred some form of herd immunity.” The best strategy, he argued, is to “gradually boost immunity” by allowing “people at low risk of severe illness to continue working” while protecting those at higher risk and scientists developing treatments and, hopefully, vaccines. The best evidence of the herd immunity effect of IPV is the experience in the United States, where IPV was introduced into common use in 1955 and replaced by OPV in 1962. Between 1955 and 1962, the number of cases of paralytic and non-paralytic poliomyelitis declined sharply (Figure 27-5). The apparent decline in the number of observed cases exceeded expectations based on the percentage of children vaccinated (Figure 27-6).214 More specific regional data have been published indicating a sharper-than-expected decline in polio cases.215 The new definition of “vaccine” released in May reads: “a preparation administered – such as by injection – to stimulate the body`s immune response against a specific infectious agent or disease.” At the time of writing, other leading medical organizations have not signed the WHO`s distorted definition of herd immunity.