What Do We Know about Natural Immunity?

Key Takeaways:

Until we have more data –

(1) If you have not had COVID-19 and are unvaccinated, you and your family, friends and loved ones are at risk. Please get vaccinated as soon as possible.

(2) if you previously had COVID-19, we cannot tell you how much or little protection you may have against reinfection, and whether reinfection might cause more severe disease, so please get at least one dose of vaccine.  

(3) The vaccine is safe and effective. As Governor Little said, “Since the COVID-19 vaccine was made widely available to everyone in May, nearly all new COVID-19 cases, hospitalizations, and deaths are among the unvaccinated.”

The science around COVID continues to evolve and our understanding regarding natural immunity vs. vaccine-induced immunity is limited by what science is available at this time to evaluate effectiveness. There is no question that there remains much that we do not yet know.

1. There are conflicting data from studies looking at the strength and durability of natural immunity. These studies often involve only one vaccine, and any conclusions from these studies cannot be assumed to be the same for other COVID vaccines. These studies also have taken place in different countries at different times, where the virus variants may differ. It is not yet clear whether the strength and duration of immunity may vary depending upon which variant someone was infected with.
2. The fact that some people who have recovered from COVID appear to have robust immunity that lasts for many months is a very good thing, although I do not want anyone to get infected in the first place and risk the fate of nearly 700,000 Americans who have died from COVID or the fate of many others who are suffering the long-term consequences of COVID. But I certainly am happy that it appears few will be reinfected, at least with the variants that we have encountered thus far.
3. Getting COVID and developing natural immunity (immunity from infection) is far more dangerous than getting vaccinated and developing vaccine-induced immunity.
4. COVID has caused many hospitalizations, deaths and in many cases long-term complications, such as so-called “long-COVID.”
5. While some studies look back at populations of people who have had COVID and have seen evidence of strong immunity, it should be noted that natural immunity is variable – some people develop more protection for a longer period of time than others. The problem is that we have no practical way as of today to identify those persons who have recovered from COVID that are likely to have strong immunity. The fact that someone may have a positive antibody test, does not necessarily mean that the person is protected from reinfection, nor that any protection the person does have will protect against future variants.
6. Antibody tests are qualitative (positive or negative) and do not indicate immunity. Even those that are quantitative and provide an antibody titer are not standardized and we do not yet know the titer that would indicate protection from infection.
7. Studies have looked at the natural immunity of persons who, in most cases, had symptomatic COVID.  We do not have sufficient data to determine whether those who previously had asymptomatic infection or those who had severe disease have robust and durable immunity. There are reasons based upon our knowledge of immunology to believe that it could be different for these persons.
8. There is some waning of immunity with natural infection. It is likely that this period of time may differ among individuals, though one interesting model published in the Lancet suggests that those with natural immunity are likely to be reinfected in a median of 16 months from the time of their peak antibody response.
9. Some reinfections can result in more severe disease with the reinfection than were experienced with the initial infection.
10. Even those who previously had COVID appear to benefit from at least a single dose of vaccine.
11. For those with prior COVID, we do not know how long the protection will last and how effective it will be against future variants.