Extended interview: expert explains how COVID-19 vaccines work and side effects after injections
Dr. Williams Moss, an epidemiologist and executive director of the Johns Hopkins International Vaccine Access Center, explains how Pfizer and Moderna’s mRNA vaccines work and why side effects are more likely after the second dose.
As the vaccination campaign against COVID-19 continues and more people receive their second dose, many reported that it caused more intense side effects than after the first. But vaccine experts say this news is normal and expected.
“It is a sign that your immune system is working,” said Dr. Williams Moss, an epidemiologist and executive director of the Johns Hopkins International Vaccine Access Center.
To date, more than 35 million vaccines have been administered in the United States, and nearly 7 million have received their second and final doses, according to the United States Centers for Disease Control and Prevention.
The side effects of vaccines used in the USA, developed by Moderna and Pfizer-BioNtech, are normal signs that your body is building protection. The CDC states that flu-like symptoms are expected and can include fever, chills, headache, muscle pain and tiredness. Some may experience pain and swelling in the arm at the injection site. All side effects should go away in a few days.
In vaccine tests for Moderna and Pfizer, side effects were more frequent after the second dose. Moss said some may have had minimal symptoms or no symptoms at all with the first dose, but will experience side effects after the second because their immune systems are already ready – resulting in a more intense inflammatory reaction at the second dose.
ARCHIVE – A woman receives a Pfizer COVID-19 vaccine at a vaccination center established at Triton College in River Grove, Illinois, on February 3, 2021. (Photo by KAMIL KRZACZYNSKI / AFP via Getty Images)
Users of V-safe, the CDC’s tool for reporting side effects of the vaccine, reported more side effects within a week after receiving their second injection, compared to the first.
Mark Sussman, who recently received his second dose of the Modern vaccine, said he felt bad for about a day and a half.
“Chills, shortness of breath, muscle pain, general pain,” Sussman described to FOX 5 DC, days after receiving his second injection. Sussman added that it was not a “fully developed flu”, but the side effects lasted about 36 hours.
But not everyone experiences side effects. Sussman’s mother also recently received a second dose of the Pfizer vaccine and felt good.
How does the COVID-19 vaccine work and why do we experience side effects?
There are peak proteins on the surface of SARS-CoV-2, the virus that causes COVID-19, which are essential for the virus to bind to cells in the body and replicate. All developed COVID-19 vaccines act to induce an immune response against the peak protein, mainly by means of antibodies.
The Moderna and Pfizer vaccines administered in the United States are mRNA vaccines. This is a new technology, but not unknown, as scientists have been working on mRNA technology for more than a decade.
Instead of injecting the virus, Moss explained that mRNA vaccines work by injecting a “recipe” for the spike protein, or the genetic code, to get cells to produce the spike protein.
“Through this mechanism, our own cells that produce the spike protein, so what happens is that our immune system will see that protein and recognize it as foreign,” triggering an immune response, he said.
This immune response is widely known as inflammation, which can result in side effects such as redness, swelling and tenderness at the injection site. It can also mean a broader systemic response in the body, such as fever, headache, muscle pain, joint pain or fatigue.
“A number of things happen in relation to inflammation, but it is really a sign that our immune system is recognizing that there is a foreign protein in our body and is preparing to fight it and get rid of it,” said Moss.
Why can some experience more side effects after the second dose?
As part of the body’s immune response, it creates memory cells known as T cells and B cells. If a virus or foreign substance enters our body again, such as the second dose of the mRNA vaccine, it is a reminder to the immune system.
“Basically, the second dose says, ‘Hey, I know you saw this peak protein a month ago. I’m going to remind you once again of what it is like to be really ready to attack it,'” said Moss. explained.
The Moderna and Pfizer vaccines are two doses, with spacing of 28 and 21 days, respectively.
The first dose of the vaccine prepares the immune system, forming an army of cells. As a result, Moss said that the second dose generates a greater immune response – hence the possibility of stronger side effects.
“We have a lot more cells available to attack you,” explained Moss. “But that’s why the inflammation can be more severe with the second dose, because our immune system is already prepared, so you get an even more intense inflammatory response.”
Does the vaccine still protect you if you don’t experience side effects?
Although side effects are usually a sign that the body’s immune system is working, those who feel good after getting the vaccine are certainly also protected.
“People who do not have moderate or severe side effects from the vaccine may still have a very protective immune response. They simply did not have this intense inflammatory response for various reasons,” said Moss, citing a combination of genetics and a previous history of exposure.
Why is the second dose of COVID-19 so important?
The two-dose dose of Pfizer and Moderna is what has been shown in clinical trials to be 94% or 95% effective in preventing the symptoms of COVID-19. Although there is some protection provided by a single dose, the protection can be significantly shorter, although it is not yet clear.
In January, the US Food and Drug Administration said that extending the time between doses or skipping the second would be “premature and have no solid roots in the available evidence”. The agency reiterated the importance of continuing the two-dose regimen at intervals of 21 and 28 days studied.
Dr. Anthony Fauci, the government’s leading infectious disease specialist, also clarified this week that the United States will “follow the science” in its clinical trials and continue to administer second doses of the Pfizer-BioNTech and Moderna vaccines within the recommended timeframe.
Fauci was responding to a debated strategy used by the UK to delay the second injection so that it can protect more people quickly with the first dose. Pfizer, one of the two vaccines approved in the country, did not endorse the decision to spacen the time between doses.
Fauci says the U.S. should maintain the current 21- and 28-day vaccine intervals for Pfizer, Moderna
Dr. Anthony Fauci said the United States should follow the data that shows optimal results, reinforcing the Pfizer vaccine at 21 days and Moderna at 28 days, despite AstraZeneca’s studies on prolonging the interval.
More than 458,000 Americans died of the virus, a higher death toll than in the entire Second World War. Nearly 27 million people in the U.S. have contracted this, some even suffering from more serious and long-term complications.
“I often say that the fundamental problem for most people … is that they underestimate the risk of the disease and overestimate the risk of the vaccine,” said Moss. “A day or two of discomfort is, in my opinion, an exchange that is worth protecting against the disease.”
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This story was reported from Cincinnati.