Covid-19 Immunity

Immunity

We don't yet know exactly how long we will be immune from Covid-19 after recovery.

• People acquire immunity either by exposure to a disease when they produce antibodies, or by vaccination.
• Our immune system remembers some infections, but forgets others. One bout of measles should give lifelong immunity, so vaccination is a good strategy. The four viruses that produce the common cold give short-lived immunity, and the infection is usually mild.

Covid-19 immunity. Current data points to a robust and lasting immunity (antibodies, B cells, T cells and memory cells) from trial volunteers, who are still being monitored. It is normal for an immune response to spike early on, then fall away precipitously, only to plateau after six to eight weeks. Trial data suggests that immunity could be at least a year. However, mild or asymptomatic cases might produce only short-lived local immunity in the lining of the airways. Very few cases of re-infection have been identified, and it does not appear to look like a serious problem for vaccines.

Herd immunity is when sufficient people in a population have had and recovered from a disease or have received an effective vaccination. If this figure is high enough (60% or higher?), the more vulnerable people have less chance of becoming infected. Specific diseases have different herd immunity thresholds (HIT).

• For measles, the HIT is 95%.
• For smallpox and polio, the HIT is 80% to 86%.
• For influenza, the HIT is 33% to 44%.

One estimate is that some 19 million people in the UK may already have had the infection but mass testing would be needed to support or revise this figure.

The UK population is currently (4 May 2020) about 66,720,000, so 1% is 667,201, 20% is 133,440,240, and 40% is 266,880,480.

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