The latest study by scientists at the National Institute for Communicable Diseases (NICD) has found that an analysis in trends of reinfections since the emergence of the Omicron subvariant shows a substantial increase in the reinfection risk not seen in the Delta and Beta variants.

The study was authored by some of South Africa’s foremost Covid-19 experts, including Professor Juliet Pulliam, director of the South African Centre for Epidemiological Modelling and Analysis (Sacema); Professor Jonathan Dushoff, an infectious disease expert from McMaster University in Canada; Dr Michelle Groome, Professor Anne von Gottberg, Professor Cheryl Cohen and Nevashan Govender, all from the NICD; Professor Koleka Mlisana from the National Health Laboratory Service; Professor Harry Moultrie from the University of the Witwatersrand; Siobhan Johnstone from the NICD; and Cari van Schalkwyk from Sacema.

The analysis also found that the two subvariants that are currently dominant in South Africa, BA.4 and BA.5, also caused a gradual increase in reinfections but not higher than the “original” Omicron variant, known as BA.1.

Scientists started tracking reinfection risk in January 2022, a month after Omicron was first identified in Tshwane and designated as a variant of concern by the World Health Organization.

Read more in Daily Maverick: “Omicron sub-variants likely cause of SA’s Covid-19 fifth wave: Here’s all the latest information”

According to the authors, they noted that a similar reinfection risk was not seen at a time when the Beta and Delta variants were dominant in South Africa.

For this report, they analysed data up to 31 August and found that the reinfection risk had remained constant since the first outbreak of the Omicron subvariant and that the risk had not changed as other subvariants emerged.

Omicron was first identified late in 2021. The analysed data showed that second and third infections spiked between December 2021 and January 2022.

Heightened risk

This study follows one done by Discovery Health, which investigated reinfection risks before Omicron came on the scene. It used data from the first three waves before vaccines became available.

A staff member carries an oxygen tank at Steve Biko Academic Hospital. (Photo: Gallo Images / Alet Pretorius)

The resulting analysis (of administered medical scheme member data) showed an 80% decrease in relative reinfection risk and that the risk was decreasing with each successive wave.

Read more in Daily Maverick: “Omicron subvariants rise in prevalence as South Africa’s positivity rate jumps overnight”

Discovery Health’s data showed a 20% relative possible reinfection risk within 90 days after the recovery from the first infection (with the “original” Covid-19 virus).

Further findings of this study included:

• 36.3% of patients were infected in the first and second waves; and
• 13.7% of individuals who first contracted Covid-19 during the second wave contracted the disease for a second time during South Africa’s third wave of infection.

Current SARS-CoV-2 infection numbers, released by the NICD on 8 September, show that the number of confirmed infections is still dropping, as is the number of hospital admissions as a result of complications caused by Covid-19.

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In the week up to 8 September, 1,475 cases of confirmed infections were reported. This was 5% lower than the previous week.

The number of PCR tests to confirm infection also dropped by about 6% from the previous week and has been decreasing.

The percentage of people testing positive for the virus was the highest in Limpopo (9.6%) and North West (6.1%). The other provinces’ test positivity rate was under 5%.

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There has been an increase in test positivity for the older age groups (older than 75), according to the NICD.

There was a 40% decrease in the number of new admissions in the past week compared with the week before. DM168

This story first appeared in our weekly Daily Maverick 168 newspaper, which is available countrywide for R25.