By the time you read this it will be out of date.

Why? Because every day we receive new data that causes us to rethink and rewrite our response to Covid-19, notably vaccine programs. This is good. I will explain.

Epidemiology, indeed all of public health policy and clinical research, are based on evidence. Data. Covid has highlighted one of the biggest challenges in healthcare: making wise policy and rolling out billions of dollars in programs in the knowledge that there just isn’t enough data to support the decision that must be made regardless. Covid has very publicly demonstrated how the life and death stakes of a global crisis can force health policymakers and political decision-makers to do the best they can in the knowledge that they have insufficient evidence at hand. They must choose, knowing that data will keep rolling in that may alter or even reverse their decision.

Perhaps the best example is America’s top infectious disease expert Anthony Fauci’s remark in March 2020: “There’s no reason to be walking around with a mask.” That didn’t last long, corrected because of a better understanding of the virus, how it is transmitted, and especially the role of aerosolised particle transmission.

My experience with what I used to describe as “making 100% of life and death policy decisions with 5% of the information you really need” was honed working as the senior global health policy expert at the US Agency for International Development in the US Department of State. I grappled daily with this conundrum, wearing my epidemiologist’s hat as I compiled policy papers in health and water that would influence hundreds of millions of dollars in donor aid.

My lived experience was the basis of my public health PhD thesis, “Where there is no data”.

Every day over the past year I have been tracking “what we know now that we wish we’d known then” about Covid-19, its transmission and prevention. And tracking the level of evidence that backs really important decisions relating to the pandemic.

So how do epidemiologists, clinicians and other scientists assess the weight they should place on masses of data coming from everywhere? Epidemiologists call this data “evidence”, and they rely more heavily on data that meets more stringent criteria. At the bottom of the evidence pyramid, with least confidence, is one-off, idiosyncratic data, such as case reports on individual patients: an example is the side effects a few individual patients might have experienced after vaccination. At the top is what is called “systematic” review” or “meta-analysis” – a comprehensive review and analysis with conclusions drawn only from well-constructed research projects and evaluations. Few randomised control studies have been done so data from systematic reviews is a long way off. More and better studies with different populations may reveal different vaccine efficacy and effectiveness, and change the “ranking” we are tempted to use today to compare the AstraZenica, Moderna and Pfizer vaccines.

Why does this matter? Because crisis situations call for urgent decisions. And because right now the approval, funding and adoption of a growing number of vaccines against the Covid-19 variant of coronavirus involve life and death on a global scale. Decisions can only be guided by the evidence the data provides, combined with the practicality and costs of each vaccine, and in light of the public health objectives of vaccination. A best-case scenario would be a vaccine that is cheap, single-dose, doesn’t need refrigeration, is stable over time, stops infectiousness immediately after it is administered, and is highly effective in providing immunity against all disease variants, in real-world conditions (versus under controlled conditions or on a small scale). A worst-case would be an expensive, volatile vaccine requiring two or more doses (and frequent boosters), needing extremely costly, low-temperature storage and transport, providing low immunity, and so on. You get the picture.

Where are we today? Pretty much in data limbo about some important issues. Most vaccines achieving approval and distribution have been tested and assessed in what are known as phase 3 trials – users numbering in the thousands. But not yet in real life, generating phase 4 data from very large populations, which is usually available only once a vaccine or other therapy is actually being sold in the market on a large scale.

Today’s list of “known unknowns” for vaccine alternatives includes:

There will continue to be plenty more data gaps because the Covid-19 strain simply behaves like all influenzas and mutates continuously.

However, it is also true and reassuring that scientists, researchers and clinicians have achieved astounding results in 10 months of vaccine development since early 2020, results that would normally take about 10 years. That puts the known unknowns in context. Acceleration of all aspects of Covid-19 science, clinical effects and vaccines is continuing at unprecedented speed, and the news is good, with possibly half a dozen promising vaccines already available. Scientists, researchers, clinicians and vaccine and therapeutics companies are working at a furious pace to keep up with a very smart virus that continuously evolves and evades. So what is unknown today will be known tomorrow, so to speak.

We should expect to see an ongoing gap between the data we have and the data we need as the virus mutates. Thankfully, we have much more than “5% of the data we need”, and the vaccines currently available look pretty good. Promisingly, the data keeps rolling in. And thankfully Australia has world-leading scientists, researchers, clinicians, political leaders and chief public health officers leading the pandemic response.

Scientists, researchers, public health experts and doctors are data-driven, conservative and cautious because history has proven that is the best way to protect us. Anti-vaxxers and conspiracy theorists are not.

Paradoxically, unanswered questions about Covid-19 and vaccines are reasons to trust science and vaccinate promptly. One expert explained the basic rationale for vaccinating as soon as possible: “You want to stay out of the hospital, and out of the morgue.”

So what you have just finished reading is likely to be out of date by the time you press “send” to share it with your family, friends and colleagues. And that’s a good thing.

• Abby Bloom is a director of Sydney Water Corporation, the Children’s Hospital Network and the NSW State Insurance Regulator. She is also an adjunct professor at the University of Sydney School of Public Health, the UTS Business School, and the founder of the Life Journey Manager portal Your 100 Year Life

This content first appear on the guardian

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