South Africa may have gotten off more lightly from Omicron due to widespread immunity from previous infection combined with vaccine coverage, researchers think, which may not bode well for other countries which have not completed their vaccination nor seen the worst COVID surges.
The South African Medical Research Council in collaboration with Discovery Health on Tuesday last week presented data from a large study showing that South Africans infected with Omicron are, on average, less likely to be hospitalised, and recover faster, compared to the other variants.
Their study looked at more than 200 000 COVID cases in South Africa during a Delta-driven surge in September and October, and the start of the Omicron-driven surge in November, as that variant began increasing rapidly. About a quarter of the people in the study already have a chronic illness, putting them at higher risk of severe COVID.
The researchers found a hopeful trend: The risk of hospitalisation for adults dropped 30% during the early days of the Omicron surge from the levels seen there in September and October.
“The hospital admissions during omicron, standing at 58 per 1000 infections, are the lowest of the four COVID waves, and one-third of what we experienced during the delta surge,” said Discovery Health CEO Ryan Noach.
Why was this so? One explanation could be the immunity from COVID recovery present in the population. South Africa had experienced three huge COVID surges with low vaccination rates compared to the US and Europe.
When the Omicron variant appeared, only about a quarter of the population were vaccinated but the vast majority of residents had likely already been infected with previous variants of SARS-CoV-2. This was based on the excess mortality rate observed in the country through the pandemic, and so it is thought that South Africans likely had some immunity granted by infection.
“Thus, Omicron enters a South African population with considerably more immunity than any prior SARS-CoV-2 variant,” concluded Dr Roby Bhattacharyya, an infectious disease specialist, and epidemiologist William Hanage in a recent working paper. This means that most Omicron cases are likely to be reinfections, rather than first infections.
Other countries will not have as broad a ‘coverage’ of vaccination and previous infection as South Africa. Around 125 million Americans are unvaccinated, and a recent study estimated that about 20% of Americans had been infected with COVID from the start of the pandemic, up to August, 2021.
The data therefore suggest that a minimum of 20% of Americans who are completely ‘naive’, as scientists term it, when it comes to exposure to SARS-CoV-2.
Source: NPR
