A NEW study by South African and German scientists has provided the first evidence globally that even three vaccine doses may not be sufficient to prevent infection with the Covid-19 Omicron variant.
The study, “Breakthrough infections with Sars-CoV-2 Omicron variant despite booster dose of mRNA vaccine”, was published in the medical journal The Lancet on Wednesday.
A group of scientists from Stellenbosch University (SU), Ludwig Maximilians University of Munich in Germany, UWC and UCT, as well as the National Health Laboratory Service, studied seven German visitors to Cape Town who had received three doses of vaccines yet were infected with the Omicron variant in late November 2021.
The group consisted of five women and two men, four of whom were working at different hospitals in Cape Town, while the others were on holiday. They were members of two unlinked social groups and participated in regular social life in Cape Town in compliance with applicable Covid-19 protocols.
All seven of them were fully vaccinated. Six had received two doses of the Pfizer vaccine and later a booster dose of Pfizer in five cases, and a booster dose of Moderna Spikevax in the other one. The seventh person had received an initial dose of AstraZeneca, followed by a dose of Pfizer and later a Pfizer booster. All seven had high levels of specific antibodies.
During a marked increase in infections in the Western Cape, the visitors started to experience respiratory symptoms from November 30 to December 2, 2021, and were diagnosed with the Omicron variant.
They were placed in domestic isolation and used a daily symptom diary to document the course of the disease over 21 days. All seven experienced mild or moderate symptoms in shortness of breath. Their blood oxygenation levels remained in the normal range and none required hospitalisation.
Booster doses were administered 21 to 37 weeks after the second vaccine doses, and breakthrough infections occurred 22 to 59 days thereafter.
This study is the first in the world to report, and characterise, breakthrough infections with the Omicron variant in fully vaccinated individuals after receipt of vaccine booster doses, the authors said.
They, however, emphasised that the mild to moderate symptoms experienced may suggest that boosted vaccination still provides good protection against severe disease caused by Omicron.
Professor Wolfgang Preiser, head of the Division of Medical Virology at SU’s Faculty of Medicine and Health Sciences, said: “The presence of this group of Germans in South Africa, when it became the first country to experience a pandemic wave driven by the Omicron variant, presented a unique opportunity to generate highly relevant and sorely needed information on the implications of the newly emerged variant for vaccination.
“Only an established, tried and tested network of collaborating scientists at three different Capetonian universities, each specialising in a different aspect, made this study possible.”
The study's findings support the need for updated vaccines to provide better protection against infection with the Omicron variant and emphasise that non-pharmaceutical measures should be maintained for now. Encouragingly, early data from South Africa subsequently suggested maintained, if reduced, effectiveness of the Pfizer vaccine against hospitalisation.