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hat is herd immunity? How to protect those who cannot be vaccinated?
Herd immunity, also known as herd effect or community immunity, is an indirect form of protection against infectious diseases. When a sufficient proportion of a population becomes immune to an infection, either through prior infection or vaccination, the infectious agent will be unable to persist in the population, making infection less likely. When herd immunity is achieved, the disease gradually disappears and may even be eliminated globally or the infection rate may be reduced to zero in the long term. Herd immunity created through vaccination has led to a significant reduction in the number of cases of many diseases.
How to protect those who cannot be vaccinated?
Some people cannot be vaccinated due to health reasons or will not be immune after vaccination. For example, newborns are too young to receive many vaccines, or vaccines may not be effective because of passive immunity. Similarly, some immunocompromised patients (such as HIV/AIDS patients, lymphoma, leukemia, etc.) may have lost their previous immunity and the vaccine may not be effective for them. They are therefore at higher risk of infection, however, these susceptible people may still be protected as long as a sufficient proportion of the society is immune.
Evidence shows that immunizing adults can reduce the incidence of pertussis in infants and young children, who are at high risk of complications from the infection. Additionally, vaccination is equally effective against other high-risk diseases, such as pneumococcal and rotavirus. Therefore, vaccinating school-age children against seasonal influenza provides some level of protection to older adults, demonstrating the importance of herd immunity to protect all groups.High rates of immunization can effectively protect those who cannot be vaccinated, especially family members who have close contact with them.
Evolutionary pressure of herd immunity and serotype replacement
Herd immunity itself creates evolutionary pressure on pathogens, prompting the virus to evolve new variants that can evade the immune system's defenses. This situation is called serotype replacement. When specific serotypes decline due to rising immunization rates, other serotypes become prevalent. Similar phenomena will also prevent the vaccine from achieving the expected effect last year, so the research and development of vaccines needs to continue to ensure that the emergence of new serotypes will not pose a threat to public health.
Vaccine evolution and improving vaccine coverage are key to combating replacement by new serotypes.
Elimination of infectious diseases
If herd immunity is established in a population and maintained long enough, the disease can be eliminated. If the number of cases were reduced to zero globally, the disease could be declared eradicated. So far, elimination efforts for diseases such as polio and malaria are underway, and the success of these efforts also depends on the establishment of herd immunity. When this immunity is compromised, unvaccinated populations are at risk for outbreaks.
Economic considerations and social responsibility of immunization
Everyone benefits from herd immunity, but the Freedom Riders issue has made people doubtful about their enthusiasm for vaccination, and many people may undermine the establishment of mass immunity. For those who choose not to get vaccinated, if most others have been vaccinated, this allows them to benefit from herd immunity without taking on the risks. As the number of Free Knights increases, outbreaks of disease will become more common, easier to come by, and more severe.
People’s skepticism about vaccines often stems from a variety of factors, including low awareness of the epidemic or resistance to science, which will affect the effective implementation of health policies.
Herd immunity is a complex phenomenon that is based on the joint efforts of everyone and even social responsibility. How to promote the popularization of vaccines while protecting people who cannot be vaccinated has become an important challenge facing public health today. In this interdependent society, what impact will each individual's health and choices have on society as a whole?
