Those of us who have been hoping that life can go back to some kind of normal after a vaccine is available may need to reset our expectations. The vaccines under development will protect against disease, not against infection.
What kind of immunity might a vaccine provide? For that matter, what kind of immunity does surviving Covid-19 confer? The two kinds that matter are sterilizing immunity and protective immunity. The former means that the SARS-CoV-2 virus can’t get a foothold in your body if you are re-exposed — you will not become infected. The latter means that if you encounter a load of the SARS-CoV-2 virus at a later time, you will not become sick with Covid-19, or will have milder symptoms than you might otherwise suffer. You could still become infected with the virus, and you could spread it to others.
Were you looking forward to going out to restaurants again, to bars or theaters or concerts or sports stadiums? Even after one or more vaccines are approved and you get vaccinated, say some time in 2021, doing any of those formerly everyday activities might spread the virus to you and to those you love. And you (and they) might risk a 1-in-5 chance of getting sick with Covid-19, even after two shots with the best vaccine that the world can come up with.
This sobering assessment emerges from a recent webinar in which executives from nine biopharmaceutical companies outlined the status of their clinical trials. The webinar was sponsored by the National Adult and Influenza Immunization Summit, and was summarized by This Week in Virology podcast regular Alan Dove on TWiV #663.
The companies presenting were those now running Phase II or Phase III trials of Covid-19 vaccines or expecting to enter such trials before 2020 is out; plus one (Merck) that is a month or two behind that timeline. They are:
(AstraZeneca, whose vaccine development effort also fits into the 2020 timeline, was invited but declined to participate, presumably because it didn’t want to field questions about the unanticipated pause in its Phase III trial.)
Alan Dove’s entire summary of the webinar is worth listening to, if you have the time: 44 minutes starting at 01:01:16. The part I want to highlight here is the 5 minutes beginning at 01:07:41. It puts in question the hope of “herd immunity,” whether acquired by vaccine or by recovering from Covid-19.
He explained that the companies all are shooting for a vaccine with at least 80% efficacy. The FDA has said it will entertain applications to approve candidate vaccines that achieve an efficacy of only 50%, but the companies are aiming higher than that.
So where does this leave us? In considerably better shape than we are in now. If only one infection in five leads to disease, hospitals and ICUs will no longer be overwhelmed and PPE shortages will be a thing of the past. Infections that do lead to Covid-19 disease might on average be less severe; many might be limited to the upper respiratory tract, like the common cold usually is today.
Vincent Rancaniello speculates on what might eventually become of the SARS-CoV-2 virus and its relationship to humankind — it might become the fifth common cold coronavirus.
Between now and that perhaps distant day, we just have to keep our expectations for a vaccine aligned with the reality of the situation. Unless one of the candidate vaccines is definitively shown to produce sterilizing immunity, let’s just remember that we will be getting vaccinated against Covid-19, not against SARS-CoV-2. So let’s not party like it’s 2019. Not quite yet.