How long does Immunity Last?
One of the key questions of the pandemic and one that may effect the course of the pandemic, is how long does immunity from previous infection last? Hopefully immunity induced by vaccination will induce immunity that last at least as long.
In a widely reported study by the Medical University of Innsbruck found that citizens of the ski resort of Ischgl in Austria still had antibodies to COVID-19 8 months after they had been infected.
It is believed by AGES, Austria’s main public health authority that residents and tourist in Ischgl were infected with COVID-19 in February 2020. The ski resorts of Europe were probably responsible for seeding COVID-19 across many parts of Europe as infected tourists returned home.
The Medical University of Innsbruck conducted a study in April that found 42% of Ischgl’s population had antibodies for the virus. In approximately 90% of those who tested seropositive in April, antibodies could also be detected in November.
COVID-19 immunity therefore appears to last at least 8 months.
How does previous infection affect herd immunity?
The study in Austria suggests that herd immunity may be achieved at lower levels of infection than previously thought. Ischgl a smaller 2nd wave infection rate than surrounding towns. “It seems that this immunity situation, which was somewhere between 40 and 50% (of the population) in November … actually protected the population from infection,” said virologist Dorothee van Laer.