Vaccine journalism

Base rate bias is a type of fallacy and it has been used quite often to report on stories about vaccinated people getting infected with COVID-19.

The fallacy states that “if presented with related base rate information and specific information, people tend to ignore the base rate in favor of the individuating information, rather than correctly integrating the two.”

There are reports appearing recently in mainstream news outlets that illustrate this fallacy. One headline states: “Delta variant is infecting vaccinated people, says Israel.” Another report states: “Delta variant is infecting vaccinated people, representing as many as 50% of new cases. But they’re less severe.” Even with that qualification by the latter sentence, the report still suffers what data analysts call the ‘base rate bias’.

To be sure, there is nothing false in the report. It is true that nearly half of infected people in Israel were vaccinated. But that is vastly different from saying “half of vaccinated people were infected,” which is not true, but is something that comes to the mind of many people when they think about the report.

I’m sorry if this seems confusing. Just bear with me for a minute because I promise to make it clear before the end.

In reporting about this particularly story, news media tends to focus on the fact that “half of infected people were vaccinated.”

Let’s do the math. Around 57% of the population of Israel are fully vaccinated against COVID-19. If we exclude the children in the count, we can say that most of Israel’s adult population (85%) have been fully vaccinated.

That’s far too many vaccinated adults compared to unvaccinated adults to merely state that “half of vaccinated people were infected.” Because that ignores the more important fact (the base rate) that only 2% of vaccinated people in Israel were infected compared to 13% among the unvaccinated, which according to epidemiologists, translate to an efficacy rate of 85% for the Pfizer vaccine.

In other words, percentage-wise, there are far more many unvaccinated people getting infected with COVID-19 than the vaccinated ones. And that still does not consider the severity of the infection between the two groups. Doctors have observed that the infections among vaccinated people do not appear to be as severe as they are in unvaccinated people.

What this means is that even if you are already vaccinated, for as long as so many others around you are unvaccinated, you must still practice the minimum health protocols; masking, distancing, and personal hygiene.

In Indonesia, it has been reported that doctors who got vaccinated with Sinovac still got sick with the Delta variant and that around 20 of them died. There are reports about this specific information yet the same reports are silent about the general information on prevalence of severe or fatal cases among those vaccinated compared to those unvaccinated.

The fact is that it is still the unvaccinated population that is driving the surge in COVID-19 cases and hospitalizations. The unvaccinated are still the weakest part of the chain where the virus can mutate into new and possibly deadlier strains.

There are people who are looking for just about any reason not to get vaccinated. And there are those who believe in conspiracy theories and spread false information about the vaccines.

For us in the media, a few cases of vaccinated people getting sick may be newsworthy. But by focusing on that specific information without putting it into context with the base rate information, we are actually helping those who spread false information.