Preliminary data on AstraZeneca’s COVID-19 vaccine in South Africa – where the coronavirus variant B.1.351 / 501Y.V2 is widespread – led the government to reconsider the vaccination and raised further international concerns about the variant. .
But the small study has so many limitations and reservations, experts warn that it is difficult to draw any conclusions from it.
The study, which was not published in a press conference or peer-reviewed on Sunday, began in June and enrolled only about 2,000 participants, about half of whom received a placebo. Early in the study – before B.1.351 emerged – the vaccine appears to be more than 70 percent effective in preventing mild to moderate cases of COVID-19. This is largely in line with the conclusion of an international Phase III trial released by AstraZeneca and co-developer of the vaccine, Oxford University, which showed mixed results for the vaccine-based adenovirus-based vaccine, but a general efficiency of about 70 percent.
But by the end of the year – when cases of B.1.351 began to rise – the South African results changed dramatically. The overall efficacy of the vaccine dropped to just 22 percent against mild to moderate COVID-19. In an analysis comparing efficacy exclusively in cases known to be due to B.1.351, the vaccine performed even worse and showed an abysmal efficacy of only 10 percent.
At first glance, these numbers are alarming, suggesting that the B.1.351 variant has rendered the otherwise effective vaccine almost useless. But, on closer inspection, these numbers are almost uninterpretable. The trial was just too small to produce statistically good results. Thus, each efficiency calculation has large confidence intervals. The final efficacy of the vaccine of 22 percent – based on a total of 42 coronavirus infections in the trial – for example, has a probable estimate of between -50 percent effective and 60 percent effective.
Delaying questions
The study was also not designed to answer the critical question of whether the vaccine can prevent serious illness, hospitalization and death. The people enrolled at the trial were relatively young – the average age of 31 – with a low underlying condition. Both of these factors make people much less likely to develop severe COVID-19 and die from the disease.
Experts emphasize that the prevention of serious diseases and death is the main purpose of vaccines – not the transmission of or mild diseases. Last month, Johnson and Johnson announced that the vaccine, like an adenovirus-based vaccine, such as that of AstraZeneca, is only 57 percent effective against moderate to severe COVID-19 in South Africa. But experts welcomed the finding that it was 85 percent effective in preventing serious illness and death. And the company reported that no one who was vaccinated in the Phase III trial was eventually admitted to the hospital or died of the disease. Many experts have advocated the as yet unauthorized vaccine as a potential new tool to end the pandemic.
The critical looming question now is whether AstraZeneca’s vaccine will also protect against serious illness and death in cases involving B.1.351, which has now been detected in more than 30 countries. Given the uncertainty, researchers and officials in South Africa said on Sunday that they would temporarily suspend the roll-out of the AstraZeneca vaccine, which may be used in the European Union on January 29 (it has not yet been submitted to the US). Food and Drug Administration for approval.) South Africa has recently started offering it to health workers. Instead, officials are now investigating the possibility of a phase-out, which involves vaccinating only 100,000 people and monitoring them over a period of time to look at hospitalization. If the vaccine looks effective at that point, they will roll out the vaccine further.
“Simply put, we do not want to end up in a situation where we have vaccinated a million people or two million people with a vaccine that may not be effective in preventing hospitalization and serious illnesses,” said Salim Abdool Karim, co-chair. . of South Africa’s Ministerial Advisory Committee on COVID-19, said at a press conference on Monday.