South Africa suspended the use of the AstraZeneca-Oxford coronavirus vaccine on Sunday after evidence emerged that the vaccine did not protect volunteers from the clinical trial of mild or moderate diseases caused by the most contagious virus variant that was first seen turn.
The findings were a devastating blow to the country’s efforts to combat the pandemic.
South African scientists said on Sunday that a similar problem occurred with people infected with previous versions of the coronavirus: the immunity they acquired naturally did not appear to protect them from mild or moderate cases when they were reinfected by the variant, known as B.1.351.
The developments, which took place almost a week after one million doses of the AstraZeneca-Oxford vaccine arrived in South Africa, were a huge setback for the country, where more than 46,000 people died of the virus.
They were also another sign of the dangers posed by new mutations in the coronavirus. Variant B.1.351 has spread to at least 32 countries, including the United States.
The number of cases evaluated as part of the studies outlined by South African scientists on Sunday was low, making it difficult to pinpoint how effective or not the vaccine can be against the variant.
And because the trial participants who were evaluated were relatively young and probably not seriously ill, it was impossible for scientists to determine whether the variant interfered with the AstraZeneca-Oxford vaccine’s ability to protect against severe Covid-19, hospitalizations or deaths.
The scientists said, however, that they believe the vaccine can protect against more serious cases, based on the immune responses detected in blood samples from people who received it. If other studies show that this is the case, South African health officials will consider resuming use of the AstraZeneca-Oxford vaccine, they said.
The new research findings were not published in a scientific journal. But the discovery that the AstraZeneca-Oxford product has shown minimal effectiveness in preventing mild and moderate cases of the new variant has added to the growing evidence that B.1.351 makes current vaccines less effective.
Pfizer and Moderna said that preliminary laboratory studies indicate that their vaccines, while protective, are less effective against B.1.351. Novavax and Johnson & Johnson also sequenced test samples from their clinical trial participants in South Africa, where B.1.351 caused the vast majority of cases, and both reported less effectiveness there than in the United States.
“These results are a reality check,” said Shabir Madhi, a virologist at the University of Witwatersrand who conducted the AstraZeneca-Oxford vaccine trial in South Africa, on the findings released on Sunday.
The pause in the launch of the AstraZeneca-Oxford vaccine in the country means that the first shipments will now be placed in deposits.
Instead, South African health officials said they would inoculate healthcare professionals in the coming weeks with the Johnson & Johnson vaccine, which has shown strong effectiveness in preventing serious cases and hospitalizations caused by the new variant.
Johnson & Johnson has applied for an emergency use permit in South Africa. But health officials have indicated that even before being authorized, some health professionals could receive the vaccine as part of an ongoing trial.
In the AstraZeneca-Oxford study in South Africa, about 2,000 participants received two doses of the vaccine or placebo injections.
There was virtually no difference in the number of people in the vaccine and placebo groups who were infected with B.1.351, suggesting that the vaccine did little to protect against the new variant. Nineteen of the 748 people in the group that received the vaccine were infected with the new variant, compared with 20 of 714 people in the group that received the placebo.
This equates to a vaccine effectiveness of 10 percent, although scientists did not have enough statistical confidence to know with certainty whether that number would remain among more people.
The researchers also conducted laboratory experiments on blood samples from people who were vaccinated and found a significant reduction in the activity levels of antibodies generated by the vaccine against variant B.1.351 compared to other strains.
In addition to the worrying news about the AstraZeneca-Oxford vaccine, Dr. Madhi reported evidence suggesting that infection with previous versions of the coronavirus did not protect people in South Africa from variant B.1.351.
To determine who had already been infected with the coronavirus, the researchers tested blood samples from people who had enrolled in a trial with the Novavax vaccine, but who received injections of placebo and not the vaccine itself.
The researchers compared levels of infection with the new variant in people who showed evidence of having already had Covid-19 with levels of infection in people who did not and did not find any difference.
This suggested, Dr. Madhi wrote on a slide presented on Sunday night, that “past infection by ‘original’ SARS-CoV-2 variants DO NOT protect against mild and moderate Covid-19 variant B.1.351.”
He said it is possible that the potential of variant B.1.351 to prevent immune responses in people who had already been infected is responsible, at least in part, for why South Africa has suffered such a devastating second wave of the virus in recent months.
Researchers at the University of Oxford on Sunday acknowledged that the vaccine provided “minimal protection” against mild or moderate cases involving variant B.1.351. They are working to produce a new version of the vaccine that could protect against the most dangerous mutations of variant B.1.351 and said they hope it will be ready in the fall.
“This study confirms that the pandemic coronavirus will find ways to continue to spread in vaccinated populations, as expected,” said Andrew Pollard, the lead investigator for the Oxford vaccine trial, in a statement. “But, with the promising results of other studies in South Africa using a similar viral vector, vaccines can continue to lessen the impact on health systems by preventing serious illnesses.”
Moderna also began to develop a new form of its vaccine that could be used as a booster injection against the variant in South Africa.
B.1.351 has become the dominant form of the virus in South Africa and has been found in several dozen countries. A small number of cases have been reported in South Carolina, Maryland and Virginia.
Scientists believe that B.1.351 may be more adept at evading the protective antibodies generated by the vaccine because it has acquired a mutation, known as E484K, that makes it more difficult for antibodies to cling to the virus and prevent it from entering cells .
Novavax said its vaccine was just under 50 percent effective in preventing Covid-19 in its South Africa trial. Johnson & Johnson reported that its single dose vaccine was 57% effective in preventing moderate to in South Africa, although it still offered complete protection against hospitalization and death after four weeks.
Another variant of the rapidly spreading virus, known as B.1.1.7 and identified for the first time in Britain, does not appear to interfere with vaccines. All five major vaccines, and most recently the AstraZeneca product, offer similar levels of protection against B.1.1.7 compared to previous strains of the virus.
The AstraZeneca vaccine has been authorized by about 50 countries, including Britain, which found dozens of cases of the variant seen for the first time in South Africa. Although many countries barely sequence the virus, making it difficult to know whether the variant B.1.351 has established itself there, it still does not appear to be dominant in any of the countries outside of South Africa that seek it.
In the United States, regulators are awaiting data for a large AstraZeneca-Oxford advanced clinical trial, which is expected to report results in March.