Super immunity? Discovery Health data analysis shows 98% drop in risk of COVID-19 admission for people who have both recovered from COVID-19 and who are fully vaccinated (Pfizer two-dose vaccine)

Authors:
Shirley Collie (Chief Healthcare Analytics Actuary, Discovery Health) and Jared Champion (Senior Actuary, Discovery Health)

In some circles, it's being referred to as "super immunity" - the finding that people who have previously recovered from COVID-19 seem to have a stronger immune response after being vaccinated than vaccinated people who have never had COVID-19.
Globally, scientists are investigating this phenomenon. We consider this phenomenon within the Discovery Health administered medical scheme member base.

a) First, if you have had a prior COVID-19 infection (without taking COVID-19 vaccination into account), how likely are you to get COVID-19 again?

We recently published a post about one's relative risk of reinfection after a prior bout of COVID-19, showing an 80% decrease in relative risk 90 days post recovery for individuals who had a prior infection (in South Africa's second wave of infection).

Analysing "documented prior infection" relative to "no documented prior infection" in vaccine effectiveness for protection against COVID-19, our model shows a 75% decrease in the relative risk, over all time. In other words, once a person has recovered from COVID-19, their odds of a future bout of COVID-19 are reduced by 75% (compared to people who have not had a prior COVID-19 infection).

We also note a relative risk decrease of 85% for COVID-19 admission, for people who have recovered from COVID-19, relative to individuals with no documented prior infection. This is consistent with our prior study.

This means that, once a person has recovered from COVID-19, their odds of a future COVID-19 hospital admission are reduced by 85% (compared to people who have not had a prior COVID-19 infection).

b) Now let's take vaccination into account. How much does the Pfizer vaccine seem to further protect fully vaccinated people who've had COVID-19 in the past, against a future COVID-19 admission?

For individuals who are fully vaccinated after a prior (documented) COVID-19 infection, the odds of hospital admission for COVID-19 range from 0.12 to 0.18 (see Figure 1) - compared with individuals who are unvaccinated and who haven't had a prior (documented) COVID-19 infection.

• As mentioned above, our data show that fully vaccinated scheme members, who have also recovered from COVID-19, are 85% less likely to be admitted to hospital should they contract COVID-19.
• Then, if these individuals are fully vaccinated, they benefit from a further layer of protection of between 82% to 88% against COVID-19 admission.
  • The degree of protection offered depends on when one tested positive for COVID-19 and whether they were fully vaccinated in either the 89 days after being infected, in the 90 to 179 days after infection or over 180 days after infection.

Figure 1: Odds of COVID-19 admission by number of days since documented prior infection for fully vaccinated Discovery clients

c) Further evidence from Discovery Health's database that COVID-19 vaccination is beneficial for those who have recovered from a prior COVID-19 infection

Table 1 below compares COVID-19 tests, hospital admissions and deaths for an unvaccinated and fully vaccinated population - both refer to people who have had COVID-19 before and recovered.

1. 242 medical scheme members in the unvaccinated group were admitted to hospital for COVID-19. From 90 days after first testing positive for COVID-19 onwards, within this group 113 (87 + 26) members were admitted to receive treatment for COVID-19.

2. If these 113 scheme members had been fully vaccinated, 96 of them would have avoided a COVID-19 admission (96/113 = 85%).

3. Furthermore, 14 of the 113 admitted scheme members died of COVID-19. On the other hand, no deaths were recorded in the fully vaccinated group.

Table 1: Number of COVID-19 tests, COVID-19 admissions, and COVID-19 deaths by duration since prior documented infection

All in all, this means that for people who have had COVID-19 and recovered, and then been fully vaccinated, the absolute risk of admission to hospital for future bouts of a COVID-19 infection is reduced by 98%, thanks to the combined protective effects of both natural immunity and COVID-19 vaccination.

This is compared to the original 85% protection that only a prior COVID-19 infection alone confers, showcasing a significant additional increase in absolute protection from vaccination above the protection granted by COVID-19 infection.

Conclusion

This analysis of Discovery Health data shows that for people who have recovered from COVID-19 and become fully vaccinated with the two-dose Pfizer vaccine, there is significant, additional protection against both serious COVID-19 illness (relative risk of admission to hospital) and death to be gained.

• All in all, people in this group enjoy 98% lower risk of COVID admission (compared to a lowered COVID admission risk of 85% for those people who have recovered from COVID-19 but are not fully vaccinated).

Our data reinforces reports of substantial protection (so-called "super immunity") from COVID-19 vaccination available to people who recovered from a past bout of COVID-19 infection.

• We've also published a related post in which we share Discovery Health's report on the real-world effectiveness of the Pfizer COVID-19 vaccine for the population at large.
• Even though contracting and recovering from COVID-19 confers a degree of protection from reinfection, it is important to consider the risk of adverse events linked to COVID-19 disease, which reinforce the value of vaccination in people who have recovered from COVID-19. Please refer to our thorough analysis on the risk of adverse events from COVID-19 disease versus COVID-19 vaccination.

Interested in knowing more or reporting on these findings?

Please contact us on media_relations_team@discovery.co.za to request any updated data available since publication and any further context required.

Did you find this post useful?

You may also be interested in reading another post explaining how "Home monitoring using a pulse oximeter linked to 48% lower likelihood of death in high-risk scheme members who have COVID-19". This article details our research which was recently published in the South African Medical Journal.

Interested in knowing more or reporting on these findings?

Please contact us on MEDIA_RELATIONS_TEAM@discovery.co.za to request any updated data available since publication and any further context required.