FDA approval of a Covid-19 vaccine will be only the start of a necessary series of events that should ultimately lead to individual-level protection, herd immunity, and a decline in transmission of infection. When most people develop immunity—either from previous infection or vaccination—it’s less likely that an infected individual will encounter someone susceptible to the virus. Thus, widespread immunity would reduce the likelihood of transmission. And so, by slowing the spread of infection, widespread vaccination leads to herd immunity.
Herd immunity protects those not yet immunized or infected, those whom the FDA decides should not get the vaccine, and those who develop only partial immunity from the vaccine. Therefore, herd immunity is essential to eliminating Covid-19 and reducing deaths due to infection. And, in turn, widespread acceptance of the vaccine is essential for herd immunity.
Public skepticism about a vaccine is thus a major concern and potential barrier to reducing infection. After all, substantial numbers of people already avoid routine immunizations. Most individuals who don’t accept vaccines such as routine childhood immunizations or the annual flu shot do so out of concern about side effects and doubts about effectiveness. Almost 15 percent of parents refuse recommended childhood vaccines, including the mumps-measles-rubella series, because of their belief in a link between vaccination and autism. The published study propounding this connection has been retracted and discredited, and multiple articles have since demonstrated the absence of such a link, but worries persist. Even today, susceptible children cause periodic measles outbreaks in the United States.
In recent years, the percentage of U.S. residents 18 or older who reported receiving the annual flu vaccine was between 40 percent and 45 percent. Reasons for choosing not to receive the flu vaccine include a sense of invulnerability to the illness; belief that the vaccine isn’t effective; confidence in the body’s immune system to fight infection; concern that the vaccine will make one sick; and fear of neurological damage.
An FDA-approved Covid-19 vaccine will present similar concerns. Even before a vaccine is approved, a significant portion of the public is worried about it. A recent poll of New Jersey residents, for example, found that 47 percent of respondents were somewhat confident that a vaccine will be safe and effective, 19 percent were very confident, and 28 percent were not confident.
Approval of the vaccine could lead to even less acceptance. Additional questions will doubtless arise about its effectiveness. The FDA has set the standard for approval at an historically low level—the vaccine needs to protect only half of its recipients from infection over six months. In addition, when the vaccine is approved, the duration of its effectiveness will be unknown—will it require boosters or annual reformulations? Questions will also arise about side effects beyond the six-to-nine month period that participants in the trials were observed. Such realities could dampen enthusiasm for acceptance of the vaccine.
The challenge to sufficient vaccine acceptance is intensified by government officials and scientists who have struggled with effective public-health communication. Multiple instances of erroneous communications about strategies for containment or mitigation have already led to distrust of message and messenger. Americans were initially told that masks were useless except for emergency-care providers; now we are told just as firmly that we need to wear them all the time, even at home, if we live with a vulnerable person. A year from now, how will people respond to vaccination pressure? When the general public starts hearing about side effects, even if rare, doubts about vaccine safety will inevitably grow.
Currently, government officials and scientists are speaking optimistically about FDA approval of a vaccine by the first quarter of 2021. If they are overselling the likely success of clinical trials, then failure to tell the rest of the story—the possibility of partial effectiveness, undiscovered side effects, and the persistence of new Covid cases—runs the risk of creating permanent distrust in a vaccine. Distrust and low acceptance mean that we could wind up, despite having an effective vaccine, a long way from herd immunity.