The appeal of a vaccine extends beyond protection of the individual: Once a large portion of a population is vaccinated, the pathogen cannot spread easily from person to person. As the pathogen is unable to gain a foothold to cause an outbreak, the entire community is protected, even those who may not be vaccinated. This concept, known as community or herd immunity , is the basis for which scientists and policymakers encourage—and sometimes mandate—vaccination, particularly for highly infectious diseases.


The herd immunity threshold for viruses varies, generally requiring that 70 to 90% of the community achieves immunity, depending on the transmissibility of the disease. For example, the herd immunity threshold for measles, a highly contagious disease, is about 94%, meaning that 94% of people in the community must be vaccinated or achieve immunity through natural infection to interrupt transmission and effectively protect the community. For COVID-19 herd immunity to be achieved, experts predict that anywhere between 50 to 80% of people need immunity, which could be attained with a safe and effective vaccine. But until a vaccine becomes widely available, normalcy may not be readily achieved.


Although vaccine availability remains the key determinant in driving herd immunity, it can only be achieved if a large enough proportion of the community is willing to receive vaccination. Historically, individual unwillingness to be vaccinated has delayed vaccine uptake and subsequent herd immunity. Take, for example, the H1N1 influenza pandemic in the spring of 2009, in which nearly half of all Americans did not state that they intended on being vaccinated due to a multitude of reasons such as safety concerns and distrust of public health organizations. Recent surveys demonstrate similar public sentiment today toward COVID-19 vaccines with some geographic variability; the proportion of individuals in the United States that would consider receiving a COVID-19 vaccine is lower than that of major EU markets.



Would consider/

probably consider


Would not consider/ probably not consider




YouGov: 69%



79% (April 2020)

64% (June 2020)

Not available

Not available

Not available

Not available


Figure 2: Sentiment toward getting a COVID-19 vaccine in select markets

In the U.S., respondents explicitly cited concerns regarding transparency and safety as reasons for their hesitancy. Among AP-NORC poll respondents who would not consider a COVID-19 vaccine, about 70% cited concerns regarding safety and about 40% cited concerns about catching COVID-19 as a direct result of receiving vaccination, though none of the Operation Warp Speed candidates are inactivated virus vaccines and cannot cause infection. Given that a significant proportion of respondents are “unsure,” vaccine uptake, and thus herd immunity, is largely contingent upon the concern of these individuals being adequately addressed.


Across Asian markets, over 85% of respondents believe vaccines in general to be safe. However, following reports and perceptions of side effects, safety concerns have risen in recent years, including in China, Japan and the Philippines.


Research into select social media posts—Twitter, Tumblr, forums, blogs or reviews—conducted by ZS suggests high levels of negative sentiment toward vaccines among the American public. Among all COVID-19- and vaccine-related social media posts available from January 2020 to June 2020, the majority were negative in nature, peaking in mid-March with about 11 times more negative than positive posts. Toward vaccine manufacturers specifically, select authors expressed concerns regarding safety, affordability and manufacturer motives during the clinical development process, implying that there may be some opportunity to further educate on these parameters. Though wide at the early stages of the pandemic, the gap between positive and negative posts appears to narrow in June—with negative posts about doubling the positive posts—indicating the potential for a shift in sentiment toward COVID-19 vaccines moving forward.

Further delineating the underlying concerns of the public could help us understand how to tailor public health communications to address them. Individuals who are unlikely to take a COVID-19 vaccine can generally be categorized into three groups:

  • General anti-vaccination individuals: Those who are opposed to vaccines more generally, potentially due to inherent beliefs regarding individual liberties, opposition to government intervention or perceptions that vaccines may be unsafe
  • Anti-COVID-19 vaccine-specific individuals: Those who are not opposed to vaccines generally but are unlikely to get a COVID-19 vaccine due to concerns about safety or political reasons
  • COVID-19 vaccine-hesitant individuals: Those who “probably” would not choose to get a COVID-19 vaccine, though the rationale may be unclear

Given the inherent beliefs of the general anti-vaccination group, these individuals are unlikely to engage with public health recommendations regarding a COVID-19 vaccine. To increase community uptake of a COVID-19 vaccine, it may be advisable to focus resources on the other two segments of the population.


To provide transparency that some vaccine-hesitant consumers are suggesting, public health officials and manufacturers could consider increasing both political and clinical visibility into the vaccine development process to boost public confidence. For example, while Operation Warp Speed has dedicated about $10 billion of funding in efforts to secure 300 million doses of an approved vaccine, the U.S. federal government has not publicly announced all the manufacturers with which it has partnered, or the amount of funding dedicated to each contract. Increased transparency in the program could help garner deeper trust specifically among the American public. Separately, in order to address potential safety concerns from vaccine-hesitant individuals, federal governments may consider placing a greater emphasis on the measures being taken by regulatory agencies and vaccine manufacturers to confirm the efficacy and safety of vaccine candidates, particularly given evidence suggesting that most individuals would prefer to wait longer for an effective vaccine. The recent FDA guidance on COVID-19 vaccines in development recommends that serious adverse events be monitored for at least six months after study vaccinations. However, additional information on required long-term safety measures may help assuage potential concerns that safety could be compromised in favor of speed of development.


Across the globe, hesitancy toward potential COVID-19 vaccines remains prevalent. Until a safe and effective vaccine is widely available, scientists and political leaders may need to address broader public concerns to increase immunization rates.