Natural immunity is no substitute for vaccine immunity
A better name for natural immunity is “convalescent” immunity. This is the immunity conferred by getting sick.
Some of the misconceptions about convalescent immunity stem from a preliminary study (not yet peer-reviewed) released last month that compared thousands of Israelis who had been infected or vaccinated in January or February. The vaccinated group had a 13-fold higher risk of breakthrough infection from the delta variant between June and mid-August than the previously infected group. It is worth noting that the pre-print study from Israel has some methodologic flaws; within the infectious disease community there is question about whether it will ever be published formally.
Nevertheless, these results don’t mean you should opt for getting infected over getting vaccinated. The risk of severe illness, death and “long-haul” COVID-19 from natural infection far outweighs the risk of any serious side effects from the vaccines. This makes vaccine-induced immunity preferable to convalescent immunity under almost all circumstances. (Exceptions are those with absolute contraindication to vaccination, of which there are very few.)
The very rare side effects such as blood clots (Johnson & Johnson), and myocarditis/pericarditis (Pfizer/Comirnaty and Moderna) are much more likely to occur with the infection itself than from vaccination. In fact, the risk of vaccination can be orders of magnitude lower than the risk of infection.
We know that reinfection or repeat illness from COVID-19 does happen, including after natural infection. And that those who were vaccinated following recovery from their illness were 2.3 times less likely to get COVID-19 again than those people who relied on convalescent immunity alone.
Similarly, vaccination following infection broadens the depth of the immune response and more protection against variants. Generally speaking, the more times the immune system has a chance to safely respond to a pathogen, the better the immune response to it in the future.
Booster shots following vaccination act similarly. Having a mild case of COVID-19 the first time around has been linked to increased risk of reinfection, and having a mild case does not predict that future infections will also be mild. We have seen cases of severe disease from COVID-19 in patients who recovered from mild infection earlier in the pandemic.
There are no data to show that getting vaccinated after an infection causes any harm. A Centers for Disease Control and Prevention study of thousands of Kentucky residents who were infected with COVID-19 last year found that those who did not get vaccinated after being infected were more than twice as likely to contract COVID-19 than those who were fully vaccinated after recovering from COVID 19.
What all this means is that it is especially risky to rely on convalescent immunity if someone has not had the disease, but it is also risky to rely on convalescent immunity if you have had the disease. Whether you have had COVID or not, it makes sense to get vaccinated.
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