How Much Immunity Does Previous Infections Offer?

Epicentre News • 01 June 2022 (Updated)

97% of South Africans have antibodies to COVID-19 due to vaccination and/or infection (Bingham et al., 2022). This is a big jump from the 45% overall immunity we found in our HUTS 1 Study in Nov 2020 to April 2021.

Evidence of this immunity was found in a survey done with 3395 blood donors in South Africa in Mid-March 2022 (Bingham et al., 2022).

Yet despite these high prevalence rates, we still had a 5th Wave. This was seen clearly in our testing numbers at our Walk-In Lab and in newspaper headlines, across the country.

It’s very encouraging that authors of a study conducted among people who recovered from a mild COVID infection were reported to have a strong antigen-specific, long-lived protection (Kojimaa and, Klausner, 2021).

Studies show that protection from reinfection is strong and could last for more than 10 months; but it is not known exactly how long that protective immunity will truly last (Kojimaa and, Klausner, 2021).

Scientists are unsure because, many systemic viral infections, like measles for example, give long-term, if not lifelong, immunity; whereas others, like influenza (the flu), give short term protection due to changes in viral genetics (Kojimaa and, Klausner, 2021).

So, without evidence to back up educated guesses (hypothesis), it’s difficult for experts to accurately know and make a solid prediction on how long just a past infection’s immunity will last and how effective it might be against often very mutated future variants.

As advised by our resident epidemiologist, the original strain of Omicron (BA.1), has shown evidence (which is currently under investigation by South African health authorities), that it does not provide adequate against its sub-variants BA.4 & 5. This has led numerous South Africans to get infected in December and infected again during the latest wave (read more here).

In keeping with other studies, Hall et al., (2022), found that if a previous infection’s immunity is combined with a 1 or more doses of a vaccine it gives much higher protection.

They saw the highest and most durable levels of protection from a COVID infection in their large study of 35 768 participants, among those who had received one or two doses of vaccine after a COVID infection (Hall et al., 2022).