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Two doses of the Pfizer-BioNTech or AstraZeneca Covid-19 vaccines are highly effective against delta-type hospitalizations for the coronavirus, according to a new analysis from Public Health England released on Monday.
The variant, which was first identified in India, has become the dominant breed in the United Kingdom. A previous analysis from PHE suggested that a single dose of the vaccine was less effective against disease symptoms caused by the delta variant than the so-called alpha variant, or B.1.1.7, that swept the UK in the winter.
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The new analysis found that two doses of the Pfizer vaccine were 96 percent effective against hospitalization from the delta variant, and two doses of the AstraZeneca vaccine were 92 percent effective.
“The second injection is crucial,” said Dr. Paul Offit, a vaccine researcher at Children’s Hospital of Philadelphia. “We know from phase I studies that the second shot induces a level of virus-specific neutralizing antibodies 10 times greater than that after the first dose.”
The PHE analysis included 14,019 cases of the delta variant in England – 166 of which resulted in hospitalization – from 12 April to 4 June.
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“These vaccines had at least astonishing efficacy in this case against hospitalization,” said Dr. Gregory Poland, director of the Vaccine Research Group at the Mayo Clinic in Rochester, Minnesota.
UK health officials have urged residents to get their second dose when it is their turn.
“It is absolutely essential to get both doses as soon as they are given to you, for maximum protection against all current and emerging variants,” Dr. Mary Ramsay, PHE’s Head of Immunization, said in a statement.
The new data “certainly suggests that full vaccination is really important for this particular species,” said Angela Rasmussen, a virologist with the University of Saskatchewan’s Vaccines and Infectious Diseases Organization.
Pfizer CEO Albert Burla expressed confidence in how Pfizer’s vaccine would work against the Delta variant on “CBS This Morning” on Monday.
“We won’t need a special vaccine for her,” he said. “The current vaccine should cover it.”
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PHE analysis provides factual evidence of the efficacy of vaccines against the delta variant. A lab study published last week in The Lancet that focused on the Pfizer vaccine found that levels of neutralizing antibodies — which fight the virus — were nearly six times lower than the delta variant compared to the original virus. The same study also found a decrease – albeit not a sharp one – in antibodies against the alpha variant, compared to the original virus.
But these lab studies don’t always translate directly to the real world. For example, a real-world study found that the Pfizer vaccine is highly effective against the alpha variant in Qatar. In fact, experts advise caution when interpreting laboratory studies on the immune system.
“The main message has to be that your immune system is incredibly complex and that it’s not just antibodies that mediate protective immunity,” Rasmussen said.
However, public health officials remain concerned about the delta variant. Data from PHE indicate that the delta variant may be 40 to 60 percent more transmissible than the alpha variant, making it the most infectious form of virus to date.
Based on what has happened in other countries, Poland said it suspects the Delta version will become dominant in the United States in the fall.
“Given what we saw in India, and then the UK, we are in great danger [the variant becoming dominant]’ He said. ‘We have a good proportion of the population that is not vaccinated and we have extensive travel.’
PHE also reported last week that the delta variant may cause more severe disease, and they were about twice as likely to be hospitalized. However, Rasmussen cautioned that more data is needed before a definitive conclusion can be made.
“It’s really difficult to determine if the virus causes more serious disease based solely on epidemiological data,” she said. “It may be because people get sick more commonly and as a result you see a higher percentage of people getting severely ill.”
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Akshay Sial, MD
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