COVID-19 vaccine barriers: Efficacy, availability and acceptability

The key goal of vaccines has been to create herd immunity, sufficient protection in the community to prevent further transmission, even among those unvaccinated susceptibles. For the novel coronavirus, the herd immunity target is around 70 percent. In the U.S., one of the president’s advisers, Scott Atlas, advocated for naturally-acquired infection to achieve herd immunity.

However, since only 10 percent of Americans have infection-related immunity, we would still need 60 percent more of the population to be infected – 180 million cases, with an associated death count of 900,000 to 1.8 million (0.5 percent to 1 percent crude mortality). This approach has recently been promoted by the Great Barrington Declaration’s signatories, three professors at Harvard, Oxford and Stanford, respectively. A much safer pathway – the compelling strategy- is through a vaccine.

However, for vaccine-related immunity, we need to have reached two important thresholds: a safe and efficacious vaccine and a high level of public acceptance. For example, if a new vaccine had only a 50 percent efficacy and only 50 percent of Americans accepted the vaccine, the population’s incremental proportion with immunity would be only 25 percent (0.5 times 0.5 or .25). Looking at possible combinations, one can see that the incrementally-required herd immunity of 60 percent can only be accomplished by having a vaccine with at least 90 percent efficacy plus a population acceptance of at least 70 percent.

A recent Pew survey suggested that the number of Americans willing to accept a COVID-19 vaccine is 50 percent, down from over 70 percent a few months ago.  he early errors of the CDC with its flawed testing kits, subsequent failure to stand up against the White House’s denigrating political pressures and questions about the FDA’s independence have created mistrust in the public health agencies that will negatively influence greater vaccine acceptance.

Anthropologist Heidi Larson has said that the key to convincing vaccine-hesitant people is to restore trust, not reflexly ascribe to them ignorance, denial, or hubris. It is in the interest of vaccine manufacturers to be transparent about the details of their protocols and avoid premature announcements about the vaccine before outside panels of experts verify it. On Sept. 5, Governor Cuomo of New York said he would create his own expert team to review any FDA-approved vaccine before endorsing it for New Yorkers.

Even if highly efficacious, a vaccine requires nationally-coordinated distribution efforts. Most require two doses, and it is not clear how long immunity will last. If 20 million doses of a perfect vaccine arrive in January, that would be enough for only 10 million people (3 percent of the population). When 200 million doses become available, that would serve 100 million (33 percent). Only when we have 400 million doses could we vaccinate 200 million vaccine advocates and reach herd immunity (68 percent).

We should prepare for another 9-12 months of disruption, despite the anticipated arrival of a safe and effective vaccine. In the meantime, public health authorities need to address vaccine-hesitancy. We may be tempted to relax some of the mitigation precautions we have lived with when a new vaccine for COVID-19 is announced. That would be a huge error. We still have too many Americans with no immunity, fully vulnerable to this unforgiving virus. Transmission is not quickly going away.

We know what works to protect us: masks, physical distancing, avoiding crowds, staying outdoors, hand washing and hard surface disinfection. Perhaps we can institute more focused intervention methods than at the beginning of the pandemic. But targeted efforts would require more testing with a quick turnaround, more contact tracing with the rapid quarantine of contacts and isolation of infected people, more public health spine, more transparency from pharmaceutical companies, and more science and truth from the White House.

Richard P. Wenzel, M.D., MSc, is an infectious disease epidemiologist at Virginia Commonwealth University in Richmond. He is editor-at-large of The New England Journal of Medicine. Wenzel also serves as emeritus professor and former Chair of the Department of Internal Medicine at VCU and has been the president of both the Society for Healthcare Epidemiologists of America and The International Society for Infectious Diseases.