Immunity to Covid Is Still Present 12 Months After Infection

Back in October of 2020, the John Snow Memorandum was published as a letter in the Lancet. Originally co-signed by 31 scientists, hundreds of others have since added their names.

Although it does not explicitly name the Great Barrington Declaration, the Memorandum is widely understood as a response to that document. It refers to “a so-called herd immunity approach”, which proponents claim “would lead to the development of infection-acquired population immunity in the low-risk population”.

However, the Memorandum states: “This is a dangerous fallacy unsupported by scientific evidence.” And it goes on to claim “there is no evidence for lasting protective immunity to SARS-CoV-2 following natural infection”.

According to the organisers’ website, more than 6,900 scientists, researchers and healthcare professionals have signed the Memorandum to date (including names from Oxford and Harvard). So almost 7,000 people with supposed expertise deemed it plausible that natural immunity would not provide any lasting protection against reinfection.

Incidentally, the language used in the Memorandum may be partly responsible for the Great Barrington Declaration being mischaracterised as a ‘herd immunity strategy’. As the authors have been at pains to point out, this is like describing a pilot’s plan to land a plane as a ‘gravity strategy’. (Their approach is more properly described as ‘focused protection’.)

It’s now one year on from the John Snow Memorandum. Is there any evidence for “lasting protective immunity to SARS-CoV-2 following natural infection”? Yes, in fact, there is.

A recent systematic review (which has not yet been peer-reviewed) found that natural immunity confers a high degree of protection against reinfection. The researchers analysed 10 studies, and calculated a weight-average risk reduction of 90%.

But is this protection lasting? According to a new study published in Clinical Infectious Diseases, immunity persists for at least 12 months in the vast majority of convalescents (those who’ve previously been infected).

Chinese researchers carried out a “systematic antigen-specific immune evaluation” on 74 individuals, 12 months after their original infection. They found that “humoral immunity is present within ~95% of convalescents and T-cell memory against at least one viral antigen is measurable among ~90% of subjects at 12m post-infection”.

Note: ‘humoral immunity’ refers to the type of immune response mediated by antibodies, whereas ‘cellular immunity’ refers to the type mediated by T-cells (as well as phagocytes and cytokines).

Although the researchers also had data from 28 healthy controls (individuals who’d never been infected), their sample was not large enough to estimate the protective effect of natural immunity on reinfection. Though it’s worth noting that not a single participant reported reinfection.

A study published last year analysed data on ten healthy males over a period of three decades, to see how often reinfections with seasonal coronaviruses occurred. They found that the median reinfection occurred after 30 months, suggesting that protective immunity lasts for years, not decades.

If SARS-CoV-2 is anything like the four other coronaviruses, we can expect immunity against reinfection to wane on a similar timescale. However, this seems more than sufficient to achieve focused protection, in the sense of shielding the vulnerable through the initial epidemic, and allowing time for treatments and vaccines to be developed.

Lockdown proponents might respond that lockdown need only have lasted as long as it took to develop the vaccines. But this argument completely ignores the costs side of the ledger. Focused protection could have worked, if only we’d bothered to try it.

Stop Press: The Brownstone Institute has compiled a list of 29 studies showing that natural immunity to SARS-CoV-2 is “robust, long-lasting, and broadly effective”.