Efficacy vs. effectiveness: The difference is important - Albuquerque Journal

Efficacy vs. effectiveness: The difference is important

In the vernacular of epidemiologists, the words “efficacy” and “effectiveness” are used quite often. Generally, the lay public doesn’t understand the nuanced difference, but the difference is quite important.

Efficacy is defined as: “a measure of the extent to which a specific intervention, like a vaccine, performs and produces a beneficial result under ideal conditions.” Effectiveness is defined as: “a measure of the extent to which a specific intervention performs and produces a beneficial result when deployed in the field under routine circumstances.” The difference between ideal conditions and routine circumstances is the fly in the ointment.

I’ve worked in global health for over 45 years, and one of the key lessons I have learned is: tools are only as good as they can be applied. Health systems – things that include health care workers, vaccines, medicines, staff, cold chain apparatus, supplies, transport, outreach sites, ongoing surveillance, evaluation and the like – are the pillars of effectiveness.

The front-runner vaccines, Pfizer/BioNTec, Moderna, and Oxford/AstraZeneca, all work at efficacy rates of 70%-95%. At this point we assume they are safe and efficacious. The Pfizer vaccine received the FDA’s emergency use authorization on Dec. 11, and Moderna’s will soon follow. But I am not convinced all are effective. Here’s why:

The Pfizer vaccine must be super-cooled prior to administration at – 94 degrees Fahrenheit; that’s really cold. The Moderna vaccine can be kept at -4 degrees Fahrenheit, a normal home freezer temperature. The AstraZeneca vaccine can be kept for six months at about +40 degrees Fahrenheit, basically on a shelf in a cool place. Storage temperature requirements are quite important in terms of delivery. Furthermore, the production burden of the Pfizer, Moderna and other vaccines is a Herculean if not a Sisyphean task. It’s estimated the United States alone will require 650 million to 850 million vaccine doses given the two-dose regimen, vaccine efficacy and considerable vaccine hesitancy in the U.S. population. New Mexico will require about 3 million vaccine doses – two doses/person – to immunize 70% of our population, not a gigantic number, which is in our favor.

So why is this important to New Mexico? Well, because we are presently slated to receive the Pfizer vaccine in the coming days/weeks. It is important because statewide, New Mexico is experiencing strained capacities due to COVID-19 in its overall health system, including health professional and management staff, facility outreach including pharmacies, and the availability/maintenance of a “super” cold chain. Furthermore, disparities among our counties are clear, and relate directly to our health system’s statewide vigor.

Thus, 1) it is important we have a vaccine with high efficacy approaching 90%; 2) we need a vaccine that can be stored and delivered through a statewide cold chain we already have available; 3) we need a vaccine that is available and affordable to all our citizens on a recurrent basis; 4) we need a vaccine that can be delivered statewide by competent staff without unduly special requirements.

In my opinion, the Pfizer vaccine is good, but not the best choice for New Mexico. Assuming the Moderna vaccine is approved, and production is adequate, our state should request this “more effective” vaccine now and for the foreseeable future based on its efficacy and less complicated cold chain requirements. Furthermore, we should ensure a stock of syringes and needles to deliver at least 3 million COVID-19 vaccines. Clearly we need an effective COVID-19 vaccine, but just as importantly we need an effective vaccine delivery strategy.

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