@bubu12
 

Vaccine efficacy in people who already had covid ?

Individuals with a known history of SARS-CoV-2 infection or previous diagnosis of Covid-19 were excluded from Moderna’s and Pfizer’s trials. But still 1125 (3.0%) and 675 (2.2%) of participants in Pfizer’s and Moderna’s trials, respectively, were deemed to be positive for SARS-CoV-2 at baseline.

Vaccine safety and efficacy in these recipients has not received much attention, but as increasingly large portions of many countries’ populations may be “post-Covid,” these data seem important—and all the more so as the US CDC recommends offering vaccine “regardless of history of prior symptomatic or asymptomatic SARS-CoV-2 infection.” This follows on from the agency’s conclusions, regarding Pfizer’s vaccine, that it had ≥92% efficacy and “no specific safety concerns” in people with previous SARS-CoV-2 infection.

By my count, Pfizer apparently reported 8 cases of confirmed, symptomatic Covid-19 in people positive for SARS-CoV-2 at baseline (1 in the vaccine group, 7 in the placebo group, using the differences between Tables 9 and 10) and Moderna, 1 case (placebo group ; Table 12).

But with only around four to 31 reinfections documented globally, how, in trials of tens of thousands, with median follow-up of two months, could there be nine confirmed covid-19 cases among those with SARS-CoV-2 infection at baseline ? Is this representative of meaningful vaccine efficacy, as CDC seems to have endorsed ? Or could it be something else, like prevention of covid-19 symptoms, possibly by the vaccine or by the use of medicines which suppress symptoms, and nothing to do with reinfection ?