People are excited to say that Pfizer-BioNTech’s COVID-19 vaccine is `between 90% and 95% effective’ but they are rarely specifying exactly what that means. This is feeling a frowing gap between what the public understanding of the vaccine’s effect (that it will stop the pandemic) and what scientists can say with any certainty about these new drugs.

Look at today’s news. The Washington Post (online) has a story `Your questions about the coronavirus vaccine, answered’ that serves as a FAQ on the new drugs.

The article addressed the big questions like ‘is it safe’ and ‘how does it work’. In it’s answer to ‘Will the vaccine protect me from getting the coronavirus?’ you find this sentence

It is also not yet known whether the vaccine prevents infection, as well as illness — a question with big implications for viral spread.

Then later, about 80% of the way through the article, after answering ‘yes’ to the question `Will I still need to socially distance?’ the authors write

Even after a vaccine is approved, experts say people will need to wear masks and socially distance — in part because the vaccine doses will be limited, and it will take time to immunize enough of the population to stop the virus from spreading.

This is representative of what Americans are hearing in the media, but not everyone will notice this nuance. Most people are overlooking it, their eyes blinded by the dazzling hope of a vaccine’s promise. Most peoples’ conceptual model of vaccines is based on polio and measles, two contagious diseases who vaccines have effectively stopped their spread. For these folks, the COVID-19 vaccine is going to do the same thing. They will end of the pandemic.

Indeed, results of the phase three clinical trials for the Pfizer-BioNTech and Moderna COVID-19 drugs provide strong evidence that they reduce the severity of symptoms in those who contract COVID-19. From the Fact Sheet For Healthcare Providers Administering Vaccine,

Although limited scientific information is available, based on the totality of the scientific evidence available to date, it is reasonable to believe that the Pfizer-BioNTech COVID-19 Vaccine may be effective for the prevention of COVID-19 in individuals as specified in the Full EUA Prescribing Information.

Scientists think the drugs also decrease the likelihood of contracting COVID-19. What the data do not show is their effect on the transmission of the virus by individuals who have been treated but are asymptomatic. Nobody knows how the drugs will effect the spread of the virus.

While scientists work to understand how the drugs effect tranmission, the vaccines will improve everyone’s situation. Fewer people will have severe COVID-19, and fewer people will die. If the drugs do reduce the transmissability of the virus, this will slow the pandemic and release some of the pressure on our human and technological infrastructure. But it’s not clear if the drugs will allow us to return to the new normal. For now, the drugs are ownly approved to lessen the effects of COVID-19 on those infected with SARS-CoV-2. From the official Emergency Use Authorization,

Pfizer-BioNTech COVID-19 Vaccine is authorized for use under an Emergency Use Authorization (EUA) for active immunization to prevent coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in individuals 16 years of age and older.

Nobody is trying to hide our limited understanding of this drug. And nobody is talking about the ignorance, either. Hopefully our community and elected leaders are preparing information campaigns that will help our communities set reasonable expectations for this and other vaccines.