Vaccine Coverage: The sweet spot
The globe is anxiously waiting for a COVID19 vaccine. People are making the assumption that this will be the day we don’t need to social distance. It will be the cure.
That may or may not be the case. These scientists found that this is ALL dependent on three things…
1. How effective is the vaccine? If you get a vaccine, it’s not guaranteed that it will actually work. For example, with the flu, if 100 people get the vaccine, it typically only works for 60 people (60%). This is called vaccine efficacy.
2. How many people actually get the vaccine? We will call this vaccine coverage. We live in a time of vaccine hesitancy. Public health officials are worried that hesitancy will increase because of this vaccine race. On top of this, some people just cannot get the vaccine (immunocompromised, pregnancy [sometimes], I’m sure there will be an age limit on the vaccine too).
3. What is COVID19 spread at the time of the vaccine? The effectiveness of the vaccine to halt an epidemic is dependent on how much of the population has already been exposed and the rate in which people are being exposed (R(0)). In other words, are we using this vaccine to PREVENT an outbreak? Or using it DURING an outbreak?
In a dream world, a vaccine would have 100% efficacy, 100% coverage, and be used to proactively PREVENT a pandemic. But this isn’t reality. This study ran a few models with different numbers to see what we should aim for.
What did they find?
• To PREVENT a pandemic and in the absence of other interventions, a COVID19 vaccine has to have at least 70% efficacy and 75% coverage.
• During an ONGOING pandemic and in the absence of other interventions, we need a COVID19 vaccine with at least 80% efficacy and 75% coverage.
• These numbers are high. Vaccine efficacy may be difficult to achieve, but this does not mean a lower efficacy won’t be helpful. Coverage may be more obtainable; a recent poll found that 75% of Americans said they would get a vaccine if it were safe.
Translation: “All of this suggests that a vaccine alone may not allow everything to immediately return to normal (i.e. stop social distancing), unless both vaccine efficacy and vaccination coverage are fairly high”.
We need to manage our expectations. A vaccine in combination with other public health interventions (contact tracing, mandatory masking, social distancing) will likely be the magic solution to get this thing under control.
Love, your local epidemiologist
P.S. This is a lot more in this article, so I highly suggest you reading it with your Saturday morning coffee. For example, the authors estimate how these different numbers impact productivity loss (in billions of dollars) and direct medical costs (in billions of dollars). Halting an epidemic will not only help medically, but financially and socially.
Data Source: Science conducted by the brilliant…. Bartsch et al., (2020). Vaccine efficacy needed for a COVID19 coronavirus vaccine to prevent or stop an epidemic as the sole intervention. American Journal of Preventive Medicine.