Iceland Study Shows Durable Antibody Response to SARS-CoV-2

Over 90% of people who had recovered from infection SARS-CoV-2 infection tested positive for antibodies against the virus four month after diagnosis, according to results from study conducted in Iceland that were reported today in the New England Journal of Medicine.

The results counter a handful of reports about rapid declines in antibodies after infection and serve as evidence that the infection will result in fairly durable immune response.

The researchers calculated that the infection fatality risk (deaths divided by the number of infections, diagnosed and undiagnosed) in the island country was 0.3%, which is half the 0.6% rate that has been calculated for the passengers of the Diamond Princess cruise ship and 0.66% of the rate that was calculated from data from Hubei province in China, where COVID-19 pandemic is believed to have started.

Based on their testing of serum samples from just over 30,000 people in Iceland and the widespread use of PCR testing in the country, the researchers estimated that almost half (44%) of persons infected with SARS-CoV-2 in Iceland did not get a COVID-19 diagnosis.

“We therefore conclude that, despite extensive screening by qPCR, a substantial fraction of infections were not detected, which indicates that many infected persons did not substantial systems,” wrote Daniel F. Gudbjartsson, Ph.D., and his colleagues, most of whom are affiliated with deCODE Genetics, a subsidiary of Amgen that is based in Reykjavik.

The 90% figure — 91.1% to be exact — for seropositivity came from 1,215 people who had recovered from COVID-19 and testing results showing that 1,107 had antibodies. The researchers said they were tested for antibdoies two months after a COVID-19 diagnosis with by qPCR and “remained on a plateau for the remainder of the study.”

Another conclusion of the Icelandic researchers was that household exposure was more likely to lead to infection than other types of exposure. That suggests, they wrote, that people who share a household with an infected person should not have contact during quarantine and that contacts of household members should be quarantined.

Iceland’s experience with COVID-19 experience has been quite mild. Gudbjartsson and his co-researchers estimate that 0.9% of Icelanders were infected with SARS-CoV-2, which would work out to roughly 3,240 people. The researchers report that only 10 deaths in the country have been attributed to COVID-19.