The sought-after state of herd immunity — in which widespread outbreaks are prevented because enough people in a community are immune to a disease — is complicated by open questions about the effectiveness of a future vaccine and how COVID-19 spreads.
Why it matters: Unless a sufficient level of immunity is achieved in the population, the coronavirus could circulate indefinitely and potentially flare up as future outbreaks.
Where it stands: The magic number often cited is a minimum of 60% of the population would need to have immunity.
- Right now, antibody studies indicate the world isn't close to that threshold, the NYT reports.
- In hard-hit New York, for example, a recent study found 19.9% of people tested have antibodies to SARS-CoV-2. (Though even that is debated by researchers.)
- And in Sweden, which took (controversial) relaxed measures in controlling the coronavirus, just 7.3% of Stockholm's population developed antibodies by April.
The catch: Antibodies are only meaningful to herd immunity if they provide lasting protection from a virus after someone is infected or vaccinated. But with the novel coronavirus, it's unknown how much immunity a person has after being infected — and for how long....
- While not about SARS-CoV-2, a recent study, yet to be peer-reviewed, measured the level of antibodies to four other seasonal human coronaviruses in 10 people over a period of 35 years and found