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Two doses of vaccine highly effective against Delta variant, U.K. officials say

Experts say it's absolutely vital to get the second dose of a two-dose series vaccine.
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Two doses of the Pfizer-BioNTech or the AstraZeneca Covid-19 vaccines are highly effective against hospitalization from the Delta variant of the coronavirus, according to a new analysis from Public Health England released Monday.

The variant, which was first identified in India, has become the predominant strain in the United Kingdom. A previous analysis from PHE suggested that a single dose of the vaccine was less effective against symptomatic illness caused by the Delta variant compared to the so-called Alpha variant, or B.1.1.7, which swept the U.K. 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 shot is critical,” said Dr. Paul Offit, a vaccine researcher at the Children's Hospital of Philadelphia. “We know from the phase one studies that the second shot induces a level of virus-specific neutralizing antibodies that’s about tenfold greater than that after the first dose.”

The PHE analysis included 14,019 cases caused by the Delta variant in England — 166 of which resulted in hospitalizations — from April 12 to June 4.

“These vaccines have had all along stunning efficacy at least in this case against hospitalization,” said Dr. Gregory Poland, director of the Mayo Clinic's Vaccine Research Group in Rochester, Minnesota.

U.K. health officials urged residents to get their second dose when it’s their turn.

“It is absolutely vital to get both doses as soon as they are offered to you, to gain maximum protection against all existing and emerging variants,” Dr. Mary Ramsay, head of immunization at PHE said in a statement.

The new data “certainly suggests that full vaccination is really important for this particular variant,” said Angela Rasmussen, a virologist at the University of Saskatchewan’s Vaccine and Infectious Disease Organization.

Pfizer CEO Albert Bourla expressed confidence about how the Pfizer vaccine fared against the Delta variant on “CBS This Morning” on Monday.

“We will not need a special vaccine for it,” he said. “The current vaccine should cover it.”

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The PHE analysis provides real-world evidence for how well the vaccines work against the Delta variant. A lab study published last week in The Lancet which focused on the Pfizer vaccine found that levels of neutralizing antibodies — which fight off the virus — were nearly six times lower against the Delta variant when compared to the original virus. The same study also found a reduction — though not as steep — in antibodies against the Alpha variant, compared with the original virus.

But these lab studies don’t always translate directly to the real world. For example, a real-world study found the Pfizer vaccine to be highly effective against the Alpha variant in Qatar. Indeed, experts advise caution when interpreting lab studies about the immune system.

“The main message should be that your immune system is incredibly complicated and it's not just antibodies that mediate protective immunity,” Rasmussen said.

Still, public health officials remain concerned about the Delta variant. Data from PHE suggests that the Delta variant may be 40 to 60 percent more transmissible than the Alpha variant, making it the most contagious form of the virus to date.

Based on what has happened in other countries, Poland said that he suspects the Delta variant will become dominant in the United States in the fall.

“Given what we've seen in India, and then the U.K., we are at high risk for [the variant becoming dominant],” he said. “We've got an appreciable fraction of the population that is not vaccinated and we are having widespread travel.”

PHE also reported last week the Delta variant may cause more severe disease, and those with the variant were roughly twice as likely to be hospitalized. However, Rasmussen cautioned that further data is needed before drawing a definitive conclusion.

“It's really hard to determine if a virus is causing more severe disease just based on epidemiological data,” she said. “It could be that people are getting infected more commonly and as a result you're seeing a higher proportion of people developing severe disease.”

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