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In what way could the public better understand efficacy rates of COVID-19 vaccines published by various companies, and do the efficacy rates affect a population’s herd immunity if that is the ideal goal of vaccination programs?

This article was published on
April 21, 2021

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Vaccine efficacy and vaccine effectiveness may sound similar, but are actually different terms to scientists and health professionals. According to the U.S. Centers for Disease Control and Prevention (U.S. CDC), vaccine efficacy is a term used to describe how well the vaccine protects clinical trial participants from getting sick or getting very sick. Vaccine efficacy refers to results reported from clinical trials and reflects circumstances specific to the research settings, rather than describing how well a vaccine works on the general public in real-world conditions.  So far many of the vaccine efficacy rates that have been released (ex. Moderna and Pfizer/BioNTech’s vaccine efficacy rates of ~95%) refer to how COVID-19 vaccine candidates can prevent symptomatic disease in people, not how the vaccine candidates reduce transmission. Researchers are still studying how effective the COVID-19 vaccines are in reducing transmission. “Herd immunity” refers to a given percentage of people that need to become immunized to a virus, through vaccines or through becoming infected naturally, against a virus in order to provide safety for an entire population - i.e. the herd. It’s the idea that if most people have developed immunity, then the rate of transmission will be low or non-existent. Researchers are still learning about what herd immunity for COVID-19 looks like. It is hypothesized that we may need at least 60-70% of the population vaccinated or recovered from infection in order to achieve herd immunity, but this has not yet been confirmed in real-world settings. Furthermore, the COVID-19 vaccine efficacy rates published by pharmaceutical companies do not yet tell us the exact vaccine effectiveness rates that can be expected in actual populations, and focus on how the vaccines prevent disease symptoms rather than how the vaccines reduce transmission. Researchers are still understanding how vaccine efficacy reported from clinical trials will impact herd immunity. It is currently thought that the percentage of people who agree to get vaccinated will be a more important factor for achieving herd immunity. It is important to remember that the goal of vaccination is not only to achieve herd immunity and reduce community transmission, in order to reduce the pressures on the healthcare system and protect at-risk individuals who may not be able to receive the vaccine for health reasons - vaccinations are also intended to protect individuals from getting sick or dying. Vaccinations play an important role for individual health as well as for public health on a societal level. Everyone who is able to get a vaccine is highly encouraged to do so, to help protect themselves as well as others.

Vaccine efficacy and vaccine effectiveness may sound similar, but are actually different terms to scientists and health professionals. According to the U.S. Centers for Disease Control and Prevention (U.S. CDC), vaccine efficacy is a term used to describe how well the vaccine protects clinical trial participants from getting sick or getting very sick. Vaccine efficacy refers to results reported from clinical trials and reflects circumstances specific to the research settings, rather than describing how well a vaccine works on the general public in real-world conditions.  So far many of the vaccine efficacy rates that have been released (ex. Moderna and Pfizer/BioNTech’s vaccine efficacy rates of ~95%) refer to how COVID-19 vaccine candidates can prevent symptomatic disease in people, not how the vaccine candidates reduce transmission. Researchers are still studying how effective the COVID-19 vaccines are in reducing transmission. “Herd immunity” refers to a given percentage of people that need to become immunized to a virus, through vaccines or through becoming infected naturally, against a virus in order to provide safety for an entire population - i.e. the herd. It’s the idea that if most people have developed immunity, then the rate of transmission will be low or non-existent. Researchers are still learning about what herd immunity for COVID-19 looks like. It is hypothesized that we may need at least 60-70% of the population vaccinated or recovered from infection in order to achieve herd immunity, but this has not yet been confirmed in real-world settings. Furthermore, the COVID-19 vaccine efficacy rates published by pharmaceutical companies do not yet tell us the exact vaccine effectiveness rates that can be expected in actual populations, and focus on how the vaccines prevent disease symptoms rather than how the vaccines reduce transmission. Researchers are still understanding how vaccine efficacy reported from clinical trials will impact herd immunity. It is currently thought that the percentage of people who agree to get vaccinated will be a more important factor for achieving herd immunity. It is important to remember that the goal of vaccination is not only to achieve herd immunity and reduce community transmission, in order to reduce the pressures on the healthcare system and protect at-risk individuals who may not be able to receive the vaccine for health reasons - vaccinations are also intended to protect individuals from getting sick or dying. Vaccinations play an important role for individual health as well as for public health on a societal level. Everyone who is able to get a vaccine is highly encouraged to do so, to help protect themselves as well as others.

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What our experts say

Vaccine efficacy and vaccine effectiveness may sound similar, but are actually different terms to scientists and health professionals. According to the U.S. Centers for Disease Control and Prevention (U.S. CDC), vaccine efficacy is a term used to describe how well the vaccine protects clinical trial participants from getting sick or getting very sick. Vaccine efficacy refers to results reported from clinical trials and reflects circumstances specific to the research settings, rather than describing how well a vaccine works on the general public in real-world conditions. 

So far many of the vaccine efficacy rates that have been released (ex. Moderna and Pfizer/BioNTech’s vaccine efficacy rates of ~95%) refer to how COVID-19 vaccine candidates can prevent symptomatic disease in people, not how the vaccine candidates reduce transmission. Researchers are still studying how effective the COVID-19 vaccines are in reducing transmission.

“Herd immunity” refers to a given percentage of people that need to become immunized to a virus, through vaccines or through becoming infected naturally, against a virus in order to provide safety for an entire population - i.e. the herd. It’s the idea that if most people have developed immunity, then the rate of transmission will be low or non-existent. Researchers are still learning about what herd immunity for COVID-19 looks like. It is hypothesized that we may need at least 60-70% of the population vaccinated or recovered from infection in order to achieve herd immunity, but this has not yet been confirmed in real-world settings.

Furthermore, the COVID-19 vaccine efficacy rates published by pharmaceutical companies do not yet tell us the exact vaccine effectiveness rates that can be expected in actual populations, and focus on how the vaccines prevent disease symptoms rather than how the vaccines reduce transmission. Researchers are still understanding how vaccine efficacy reported from clinical trials will impact herd immunity. It is currently thought that the percentage of people who agree to get vaccinated will be a more important factor for achieving herd immunity.

It is important to remember that the goal of vaccination is not only to achieve herd immunity and reduce community transmission, in order to reduce the pressures on the healthcare system and protect at-risk individuals who may not be able to receive the vaccine for health reasons - vaccinations are also intended to protect individuals from getting sick or dying. Vaccinations play an important role for individual health as well as for public health on a societal level. Everyone who is able to get a vaccine is highly encouraged to do so, to help protect themselves as well as others.

Context and background

There is widespread interest in how effective the COVID-19 vaccine candidates are, and how the vaccines will help contribute to herd immunity on a societal level. Unfortunately, there is also vaccine hesitancy among some people, and herd immunity depends on maximizing vaccinations among the people who are able to receive them.

Health experts have emphasized that it is more important than ever to increase access to accurate information about the vaccines, so people can make informed decisions that will protect their health. While evidence shows that the vaccines are largely safe and effective, if anyone has any remaining questions about getting the COVID-19 vaccine, they are highly encouraged to consult with their healthcare provider. 

Resources

  1. Overview of Vaccine Efficacy and Vaccine Effectiveness (WHO)
  2. Vaccine Efficacy, Effectiveness and Impact (KCE)
  3. “Herd Immunity”: A Rough Guide (CID)
  4. COVID and Herd Immunity (The Atlantic)
  5. Vaccine refusal and herd immunity (Lancet ID)

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