Discovery Health's investigation into the Pfizer COVID-19 vaccine's real-world effectiveness

4 November 2021

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.

Issued by Discovery, 4 November 2021