COVID reinfection protection

Key takeaways:

• Getting sick with COVID can give you significant immunity against getting another case that becomes severe or leads to death, but gives less protection against getting reinfected at all 
  • At 10 months after getting sick with COVID, protection against severe disease and death is 90%
  • For the Omicron variant, protection against getting reinfected 10 months later is only 36%
• Protection from past infection is at least as good as or, in many cases, more sustained than from two doses of an mRNA vaccine
  • However, vaccination is the safest way to get immunity
  • A case of COVID can present serious health risks of hospitalization or death that can be avoided through vaccination.
• Our recommendations: 
  • Annual booster shots, especially for those at higher risk of severe infection
  • Modify restrictions on access to activities (like entrance to countries) on the basis of vaccine status to take into account past infection, particularly if that past infection has been in the last 6 to 10 months

This transcript has been lightly edited for clarity

Read the research

Previous infection provides significant protection against severe disease, but less against another infection

In this version of Global Health Insights, I’d like to speak about our paper, that’s been published in The Lancet, that is a systematic analysis of all the available studies about protection that is derived from previous infection with COVID.

The first, the good news is that we find even at 10 months, the protection against severe disease and death, regardless of the variant that you are infected with, appears to be 90%. So that’s excellent, sustained protection.

The second observation from the analysis is that the protection from past infection against being infected, but not severe disease, is not as impressive. At 10 months that looks to be for the Omicron variant maybe as low as 36%.

So there’s a difference in the protection for what really matters, severe disease and death, much higher, much more sustained than being able to block transmission through immunity from past infection.

Another observation from our analysis is that there’s many fewer studies on the protection that an Omicron infection gives you against future sub-variants of Omicron. For example, a BA.1 infection against a BA.5 or BA.4, that appears to perhaps be even a little bit lower. But there aren’t that many studies.

The fourth major observation from this analysis, and perhaps a surprise to many, is that the protection from past infection is at least as good as or, in many cases, more sustained than from two doses of an mRNA vaccine, or two doses of any of the other vaccines that are out on the market.

Vaccination is the safest way to get immunity

This does not mean that you should not get vaccinated, because vaccination is the safest way to get immunity, as compared to getting infected with COVID. Even though Omicron and the sub-lineages that are around for Omicron are much less severe, as we’ve seen in China or in Hong Kong, if you have not been infected and not ever been vaccinated, then Omicron can certainly kill. And so you do want to maintain immunity, if you can, through keeping boosters up, and that’s particularly important for those that are 60 and above, or those that have major co-morbidities.

We think that the evidence of sustained protection from past infection means that restrictions on access to activities, or entrance to the United States or other countries, on the basis of vaccine status, should be modified to take into account past infection, particularly if that past infection has been in the last 6 to 10 months.

As we look ahead to thinking about managing immunity, because immunity does appear to last at least 10 months, we do agree with the suggestion that annual COVID boosters are probably appropriate, particularly for those at high risk, because we don’t yet know how long immunity from past infection will continue past 10 months.

But as data accumulates that basic notion that you get sustained protection at least for 10 months, we may end up extending that farther out.

Why does past infection seem to give sustained immunity? 

Well, it not only has, by being exposed to the actual COVID virus, we not only see different types of antibody responses, but we also think there’s probably a strong T-cell response to past infection that helps in that sustained protection.

All of this means that we really need to be more concerned in the future about the possibility of a new variant with immune escape, and that is more severe than Omicron, than being particularly concerned about ongoing waves of Omicron sub-lineages in those that have had a past infection or who are vaccinated, or both.

For those who are not vaccinated and have never been infected, you remain at high risk and it’s important to try to seek out vaccination so that you move into that category of the most of the world that have protection against severe disease, either through past infection or vaccination.