You want more evidence that post-recovery vaccination against Covid-19 reinfection helps? Here is a careful study from the U.K. that followed some 35,000 health care workers — initially without symptoms — in over 100 institutions there. Starting in June 2020 the SIREN study tested these people regularly, with blood sampling every month and nasal swabs every 2 weeks during the period when the Delta variant was the greatest threat. Almost a third of the group, although asymptomatic, showed seropositivity by the time the vaccine was introduced to the U.K. in December 2020.

Dr. Susan Hopkins, the senior author of the paper just published in the New England Journal of Medicine, explains SIREN’s results. The short version is that the vaccine was effective — up to 85% after the first dose — and its protection waned to about 50% some 6 months after a second dose. Among those who were seropositive before the arrival of the vaccine, vaccination showed a remarkable 90% effectiveness after the first dose, and that effectiveness remained high more than 18 months after their earlier infection.

New England Journal of Medicine study

[Running time: 11 minutes]

Transcript of the interview