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You have received your first dose of the Covid vaccine.  Now what?

Last Saturday, the United States hit a new record for the number of daily vaccinations: 4 million. The record breaking day came as vaccinations have steadily increased in recent weeks, bringing the daily average to more than 3 million.

This means that more and more people in the United States are receiving a dose of a Covid-19 vaccine every day. For the majority, who will receive the Pfizer-BioNTech or Moderna vaccine, this is only the first dose; in three to four weeks, they will come back for a second.

But is a person protected after only the first blow?

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Only if the vaccine was Johnson & Johnson’s single dose vaccine. For the other two vaccines currently available in the United States, experts say it is essential that people who receive a two-dose vaccine return for the second in order to be fully protected.

Partially vaccinated people should not change their behavior and instead should remain closed until they have completed their series of vaccines, said Dr Paul Offit, director of the Vaccine Education Center at the Children’s Hospital of Philadelphia and member of the Food and Drug Administration. vaccine advisory committee.

“It just scares me that we have, in every sense of the word, put forward the idea that [Pfizer and Moderna] are more than a two-dose vaccine, ”Offit said.

Last week, the Centers for Disease Control and Prevention reported that the first dose of Pfizer or Moderna vaccine was 80% effective in preventing infection. This protection was measured two weeks after the first dose, but before the second.

During a briefing from the White House Covid-19 response team on Monday, Dr Anthony Fauci, the country’s leading infectious disease specialist, qualified these results by declaring: “It’s a bit of a 80% tenuous. “

“The question,” Fauci said, “is how long [that protection] latest?”

“The best reason to wait for that second dose is that you want to achieve lasting immunity,” Offit said.

Pfizer research, published last week, showed protection lasted for at least six months in people who received both doses of the vaccine.

“Getting the second dose will be really important for lasting protection,” said Dr. Peter Hotez, co-director of the Center for Vaccine Development at Texas Children’s Hospital and dean of the National School of Tropical Medicine at Baylor College of Medicine.

Additionally, two doses of the Pfizer vaccine – not one – appear to protect against certain variants of the virus, including the variant that was first detected in South Africa, the drugmaker said last week.

It’s after the second dose, Offit said, that variant protection really kicks in.

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Offit and Hotez both said the second dose of an mRNA vaccine, like that from Pfizer and Moderna, elicits a much more robust immune response than a single dose.

The second dose tells the immune system that the coronavirus deserves a long-term response, said Michal Tal, an immunologist at Stanford University.

“For the immune system, it really matters that you keep seeing something,” she said, referring to the second dose. “If you see it again, it’s a signal that it’s worth putting in a lot of energy and making a strong response from memory.”

The Johnson & Johnson single-dose vaccine, on the other hand, leads to an equally robust immune response after a single dose.

Even so, as vaccinations have mushroomed across the country, Tal said she was increasingly questioning the need for people to come back for their second dose of the mRNA vaccine, especially if they have. felt side effects after the first one. (These side effects can range from arm pain to fever and chills, which can last up to a day or two.)

His answer is an unequivocal yes.

“The side effects you are facing are worth having this strong immune response that is going to protect you from the real virus,” she said.

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