The coronavirus vaccine developed by Pfizer and its German partner BioNTech protects against symptomatic Covid for up to six months, an updated analysis of clinical trial data has found.
In a statement released on Thursday, the companies reported efficacy of 91.3% against any symptoms of the disease in participants assessed up to six months after their second shot. The level of protection is only marginally lower than the 95% achieved soon after vaccination.
The findings are the first to demonstrate that the vaccine remains effective for many months, an outcome that doctors and scientists had desperately hoped for because it suggests that people being vaccinated now should be protected at least until the autumn when boosters may be ready.
Analysis of participants in the phase 3 trial, which has enrolled 46,307 people, identified 927 symptomatic Covid cases. Of these, 850 were in the placebo arm of the trial and 77 in the vaccine group. There were 32 cases of severe Covid, as defined by the US Centers for Disease Control and Prevention (CDC), in the placebo group, and none in the vaccinated group. More than 12,000 people vaccinated in the trial have now been followed for at least six months after their second dose.
More striking still are results from the South African arm of the trial where nine Covid cases were observed among 800 participants. All of the cases were in the placebo group, and six were confirmed to be the new “variant of concern”, B.1.351, which has worried scientists because of its ability to partially evade antibodies produced in response to vaccines or past infection. Public Health England said on Wednesday that it knew of 469 confirmed or probable cases of the South African variant in the UK.
With cases in the South African arm of the trial so low, more evidence is needed to confirm the vaccine’s protection against the new variant, but scientists were still delighted by the result. “I do regard this as a really positive indication,” said Danny Altmann, a professor of immunology at Imperial College London.
He said scientists had become “terribly worried” about the variant’s ability to evade immunity from previous infection or vaccination. “Studies like this confirm our sense that the vaccine gives such massive protective headroom that even with some loss of immunity, you’re still safe,” he said.
The chairman of Pfizer, Albert Bourla, said the latest data put the company in a position to apply to the US Food and Drugs Administration for full approval of the vaccine. The jab is currently approved under emergency use authorisation.
The results came as scientists in the UK reported strong immune responses in older people who had received two shots of the Pfizer vaccine. Blood tests on 100 people aged 80 to 96 years old revealed that 98% produced strong antibody responses after two doses of the vaccine given three weeks apart. Antibody levels more than tripled after the second shot.
The findings, released in a preprint that has yet to be peer-reviewed, will boost confidence that the Pfizer vaccine can be highly effective against Covid even in the most vulnerable older people, who tend to generate far weaker immune responses to vaccines and natural infections. Pfizer trialled its vaccine with a three-week gap between shots, but the UK leaves a three-month gap, meaning it is unclear whether the same level of protection is achieved.
Paul Moss, a professor of haematology at the University of Birmingham who led the study with Dr Helen Parry, also at Birmingham, said the team was surprised and very pleased to see the results, which tallied with the “excellent clinical protection” the Pfizer vaccine appears to provide. The first major real-world study of the Pfizer vaccine, in Israel, found that two shots prevented 94% of symptomatic cases across all age groups.
The scientists went on to examine another branch of the immune defences raised by the vaccine, known as the T-cell response. Antibodies protect against infection by gumming up the virus and preventing it from infecting cells, but T-cells destroy human cells that are already infected, and may also support antibody production over time. After both shots of the vaccine, two-thirds of the participants had detectable T-cell responses. “We know that as people age their cellular immune responses are more difficult to elicit,” said Moss. “So that is something that we will need to keep an eye on very closely.”
Further work at Public Health England’s Porton Down lab showed that blood serum taken from the volunteers after two shots of vaccine strongly neutralised the original coronavirus that spread around the world last year. But it was on average 14 times less effective against the P.1 variant first seen in Brazil, and which has now reached the UK and elsewhere.
“The variant from Brazil reduces neutralisation response, but at this early stage after the vaccine where we’re seeing such high antibody levels we are still quietly confident that this should still provide valuable protection against this variant of concern,” said Parry.
UK Officials Found 30 Blood Clot Cases in People Vaccinated with Astra Zenica
UK regulators said they have identified 30 cases of rare blood clot events after the use of Oxford-AstraZeneca vaccine.
However, the health officials said they still believe the benefits of the vaccine in the prevention of Covid-19 far outweigh any possible risk of blood clots
Some countries have restricted use of the AstraZeneca vaccine while others have resumed inoculations, as investigations into reports of rare, and sometimes severe, blood clots continue.
On March 18, the UK medicines regulator said that there had been five cases of a rare brain blood clot among 11 million administered shots.
On Thursday, it put the count at 22 reports of cerebral venous sinus thrombosis, an extremely rare brain clotting ailment, and eight reports of other clotting events associated with low blood platelets out of a total of 18.1 million doses given.
Last month, AstraZeneca did a review of more than 17 million people vaccinated in the United Kingdom and European Union, following the suspension of the use of vaccine in some countries over clotting issues.
AstraZeneca Plc said the review of safety data of people vaccinated with its Covid-19 vaccine has shown no evidence of an increased risk of blood clots.
“A careful review of all available safety data of more than 17 million people vaccinated in the European Union and UK with COVID-19 Vaccine AstraZeneca has shown no evidence of an increased risk of pulmonary embolism, deep vein thrombosis or thrombocytopenia, in any defined age group, gender, batch or in any particular country,” the company had said.
UK’s Chris Whitty: society will have to learn to live with Covid in similar way to flu
England’s chief medical officer says unrealistic to think border policy can stop new variants entering UK
The idea that Covid variants can be stopped from entering the country is “not realistic”, and Covid will eventually have to be managed in a similar manner to serious seasonal viruses such as flu, Prof Chris Whitty has said.
Speaking at a Royal Society of Medicine webinar, England’s chief medical adviser said the relaxation of Covid restrictions was likely to result in the R number rising above 1 and the risk of variants gaining a foothold and spreading increasing.
The more cases that have been imported, the quicker that will happen. As a result, Whitty said, border policies are focused on countries with more cases, or more cases of particular variants, than the UK.
“The UK is a net exporter of [the Kent] B117 variant, so other countries are understandably putting their border measures up against us to slow that down. We are a net importer of other variants that are a bit more of a worry from the vaccine point of view. That’s really what drives a lot of the policy, when it is being rational, excepting that border policy isn’t always fully rational,” he said.
Whitty said the majority of experts believed Covid was not going to go away and it would eventually have to be managed in a similar manner to flu. In a bad year, flu can kill 20,000 to 25,000 people. “It is not flu, it is a completely different disease, but the point I am making is, here is a seasonal, very dangerous disease that kills thousands of people every year and society has chosen a particular way around it,” he said.
While Whitty noted that factors such as variants and population density were important, he cautioned against trying to explain how Covid had affected different countries by focusing on just one or two factors, noting that Germany was now facing a difficult situation despite its previous success in tackling Covid largely being put down to its diagnostic capabilities.
“It is actually usually a large combination of factors, some of which are under our control, many of which are not. And more of it is chance than I think people are prepared to accept,” he said.
Whitty said new vaccine technologies meant it had become easier and quicker to tweak vaccines, which will be important for tackling new Covid variants, and he said that two years from now it was likely there would be a wide portfolio of vaccines available.
He said at present the main effort of companies was to boost vaccine supplies and there was less capacity to respond to new variants, while it was unclear whether current vaccines offer a “fair degree” of protection against severe disease and death even if they do not generate high levels of neutralising antibodies.
“What we have got to do is work out some balance which actually keeps [Covid] at a low level, minimises deaths as best we can but in a way that the population tolerates and do as much of the heavy lifting as we can by medical countermeasures,” he said.
April 2 (GMT)