Question: Tony Fauci recently said that a vaccine is unlikely to offer herd immunity, which confused me. I thought we would get herd immunity with a vaccine. What’s up with that?
Answer: In an interview with CNN last week, Dr. Fauci described two issues that would preclude herd immunity — 1) Anti-vaccination sentiment, “there is a general anti-science, anti-authority, anti-vaccine feeling among some people in this country — an alarmingly large percentage of people, relatively speaking.” and 2) Vaccine efficacy, “The best we’ve ever done is measles, which is 97 to 98 percent effective. That would be wonderful if we get there. I don’t think we will. I would settle for [a] 70, 75% effective vaccine.” In short, because the vaccine is unlikely to be fully effective against SARS-CoV-2 and because a large proportion of the population is unlikely to get the vaccine, we’ll fall well short of achieving herd immunity and the virus will continue to circulate in our communities, threatening those who are unable to get vaccinated and those for whom vaccination did not confer protection.
The need for vaccination education programs.
As this article published in the BMJ describes, the anti-vaccination movement is of grave concern for our fight against COVID-19 and other diseases. For example, a study of 1000 people in New York over 24–26 April found that “only 59% of respondents said they would get a vaccine and only 53% would give it to their children.” The expectation that we’ll miss herd immunity because of anti-vaccination sentiment calls for sweeping social behavior change efforts to disabuse people of anti-vaccination bias. Dr. Fauci calls for just that. In the CNN interview, Dr. Fauci says, “We have a [vaccination education] program right now that’s going to be extensive in reaching out to the community…” Unfortunately, this is yet another area of our government’s response that appears to be disjointed and neglected. CNN reached out to HHS for more information on the vaccination education program and reported, “Michael Caputo, an HHS spokesman, did not confirm the existence of a vaccine education campaign, adding that “I’d hate to see CNN put out [a] wildly incorrect story.”
Defining vaccine effectiveness.
In addition to hearing a lot about herd immunity (for a refresh, see Q&A of 5/1, #Herd Immunity) we’re also hearing a lot about vaccine efficacy. It’s another epidemiological term bandied about as if we all know what it means. Let me give a quick overview — vaccine effectiveness measures the reduction in disease among the vaccinated group in the real world (rather than clinical setting). For example, if a coronavirus vaccine is 75% effective, it means that we will see a 75% reduction in the number of coronavirus cases among those vaccinated. CDC offers a full definition here. In the space of partial effectiveness, even for folks who are vaccinated and still get sick, we have evidence from other vaccination studies — here, flu — that vaccination can reduce the severity of the illness.