JOHANNESBURG (REUTERS) - Two doses of Pfizer-BioNTech's Covid-19 vaccine appear to have given 70 per cent protection against hospitalisation in South Africa in recent weeks, according to a major real-world study which suggests weaker efficacy against the new Omicron variant.
The study released on Tuesday (Dec 14) by South Africa's largest private health insurance administrator, Discovery Health, was based on more than 211,000 positive Covid-19 test results.
Around 78,000 of those results from Nov 15 to Dec 7 were attributed to Omicron.
The 78,000 results are not confirmed Omicron cases, meaning the study is not able to draw conclusive findings about the variant labelled "of concern" by the World Health Organisation and reported in more than 60 countries.
South African scientists have so far confirmed around 550 Omicron sequences, with the variant accounting for 78 per cent of sequences from November, more than the previously dominant Delta variant.
South Africa alerted the world to Omicron late last month, triggering alarm that it could cause another surge in global infections, and leading to the imposition of travel restrictions on southern Africa.
South Africa's daily infections have since risen to around 20,000 in recent days.
The findings from a real-world analysis are some of the earliest on protection against Omicron outside of lab studies, which have shown reduced neutralising activity against the variant.
Based on analysis by Discovery Health's clinical research and actuarial teams, and in collaboration with South Africa's Medical Research Council (SAMRC), the real-world study calculated that two doses of Pfizer-BioNTech offered 70 per cent protection against hospitalisation during the recent surge in cases and 33 per cent protection against infection.
It said this represents a drop from 80 per cent protection against infection and compares with 93 per cent efficacy against hospital admission during South Africa’s outbreak of the Delta variant, which is the globally dominant variant and considered to be the most infectious to emerge during the pandemic.
Discovery cautioned that the study’s findings should be considered preliminary.
Dr Michael Head, senior research fellow in global health at the University of Southampton, also said there was a large degree of uncertainty for now about Omicron.
"It is important to avoid inferring too much right now from any national scenario. For example, the narrative around South Africa is that Omicron may be much milder, whereas reports out of Denmark broadly suggests the opposite," he said.
South Africa is using the Pfizer-BioNTech and Johnson & Johnson vaccines in its Covid-19 immunisation campaign, with more than 20 million Pfizer doses administered so far.
J&J and the SAMRC are conducting a large real-world study of J&J’s vaccine, and recent analysis has shown no deaths from Omicron, SAMRC President Glenda Gray said.
"So that’s the good news, it shows again that the vaccine is effective against severe disease and death," she said.
With 70 per cent or more of the South African population estimated to have been exposed to Covid-19 over the past 18 months, high estimated levels of antibodies in the population might be skewing the data.
"This could be a confounding factor for these hospital admission and severity indicators during this Omicron wave," Mr Ryan Noach, chief executive of Discovery Health, said in a briefing on the study.
The analysis also shows protection against hospital admission is maintained across all ages, in people from 18 to 79 years, with slightly lower levels of protection for the elderly, it said.
Protection against admission is also consistent across a range of chronic illnesses including diabetes, hypertension, hypercholesterolemia, and other cardiovascular diseases.
It concluded that there was a higher risk of reinfection during the fourth wave than during previous waves and that the risk of hospitalisation among adults diagnosed with Covid-19 was 29 per cent lower than during the country’s first wave early last year.
Children appeared to have a 20 per cent higher risk of hospital admission with complications during the fourth wave than during the first, despite a very low absolute incidence, it said.
"This is early data and requires careful follow up," said Ms Shirley Collie, chief health analytics actuary at Discovery Health.
However, this trend aligns with a warning a recent days from South Africa’s National Institute for Communicable Diseases (NICD) that during the country’s third wave from June to September they had seen an increase in paediatric admissions and now, in the fourth wave, they are seeing a similar increase in admissions for children under five, she said.
South African scientists have said they cannot confirm a link between Omicron and the high admissions of infants, which could be due to other factors.
Considerable uncertainties surround Omicron, first detected last month in southern Africa, whose mutations may lead to higher transmissibility and more cases of Covid-19 disease.
The WHO has said there were early signs that vaccinated and previously infected people would not build enough antibodies to ward off an Omicron infection, resulting in high transmission rates.
It is unclear whether Omicron is inherently more contagious than the globally dominant Delta variant, the WHO said.
Pfizer and BioNTech said last week that two shots of their vaccine may still protect against severe disease, because its mutations were unlikely to evade the T-cells’ response.