Glede na epidemijo Covid, ki se ne umirja, ampak kaže spet trend naraščanja ter glede na nove mutacije virusa, ki je še bolj kužen, se države danes soočajo s ključno dilemo glede strategije cepljenja: cepiti najbolj ranljive skupine ljudi tudi z drugo dozo cepiva ali pa to dozo nameniti ostalim posameznikom in tako doseči čim večjo precepljenost prebivalstva? Če se je prva varianta še pred tedni zdela kot edina relevantna in znanstveno podkrepljena, pa v luči pospešitve trenda okužba druga varianta dobiva vse večjo podporo. Če cepimo čim večji delež prebivalsstva, se bo tudi epidemija hitreje umirila.

Tim Harford v Financial Timesu to dilemo plastično opisal z metaforo razlike med kolesom in avtom. Pri kolesu potrebuješ obe kolesi, da se lahko pelješ, pri avtu pa raje vidiš, če imajo ponoči vsi avti prižgano vsaj eno luč, kot da imajo nekateri dve, drugi pa nobene. Na prvi pogled groba metafora, vendar dobro ponazori logiko dileme. Če se virus močno razširi, cepljena pa bo zgolj ozka skupina ljudi, bomo efektivno praktično vsi vozili v temi.

Seveda pa to ni vprašanje za ekonomiste, pač pa mora svoje mnenje podati stroka (v širokem spektru od infektologov, imunologov do epidemiologov). Problem je, ker danes ni podatkov o tem, katera strategija je boljša, ker se je cepljenje komaj začelo. Ne vemo, kako učinkovita so cepiva glede ustvarjanja odpornosti, kako dolgo ta traja, ali učinek izgine, če prvemu cepljenju ne sledi tudi drugo, ne vemo, kakšni so stranski učinki itd.

Potrebne so študije in testi na naključnih vzorcih. Vendar pa bomo te dobili z velikim zamikom. Prepozno. Odločitev pa je treba sprejeti danes. In pri odločitvi za strategijo “cepiti večino ljudi vsaj z eno dozo” gre zaradi neobstoja podatkov bolj kot ne za igro na srečo. Toda enako velja tudi za alternativno strategijo “cepiti najbolj ranljive dvakrat“. Nihče danes ne ve, katera je optimalna. Toda potrebna je odločitev in s prebivalstvom je treba to dilemo jasno skomunicirati in povedati, ob katerih tveganjih je bila – po posvetu s stroko – sprejeta ena ali druga strategija.

But the shift to “first dose first” creates other dangers. One is vaccine resistance. Half-vaccinated people encourage vaccine-resistant strains of the virus. Some scientists think this is a modest risk compared to the selection pressure from millions of people who have already developed some immunity after infection. Others think it is a catastrophe waiting to happen.

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So, having made this leap, the government now needs to step up its communication and its gathering of evidence. Nicole Basta, an epidemiologist at McGill University, points out that while clinical trials study the protective benefit to an individual of a vaccine, they don’t study vaccination strategies.

Those studies are now urgently needed. The University of Dundee is planning to launch a study called VAC4COVID, focusing on safety and side effects. The ZOE COVID Symptom Study app provides another window into the experiences of people who have been vaccinated.

But we need much more. We need rigorously randomised trials comparing different doses, delays between doses, and mixed-dose vaccinations too. We can also learn a lot simply by studying what happens to different people who have received different vaccination regimes. What we learn would allow the fine-tuning of mass vaccination months and years into the future.

Some of these studies will happen but I worry that many will not. Danny Altmann of Imperial College laments the lack of a large-scale monitoring effort — there seems to be no plan even for something as simple as calling people back to test their blood for antibody levels after vaccination. In any case, solid evidence will take time to assemble.

Meanwhile, there is nothing wrong with making our best guess. But the government needs to be honest with the doctors and the public about where the uncertainties lie. It needs to support rapid collection of new evidence to reduce those uncertainties. And it would be wonderful if it could shake the appearance of making things up as it goes along.

Let’s not fool ourselves into thinking that the choice is easy or the evidence is clear. “First dose first” is a gamble. So are all the alternatives.

Vir: Tim Harford, Financial Times