(CNN) So you finally got your coronavirus vaccine. It took weeks of waiting, maybe a few phone calls before winning the jackpot with a drive-through vaccination clinic. Or maybe you are a health care professional who had a chance at work.
Now comes the hard part – making sure you take your second dose in time. It means another appointment and keeping an eye on the calendar. In addition, perhaps, a little anxiety.
Doctors have warned people that the first dose can help. And now, people are starting to report that the second dose can cause more side effects than the first.
It is not an unexpected discovery. Moderna and Pfizer said in their presentations to the United States Food and Drug Administration that there was a noticeable difference in dose reactions when testing their vaccines on volunteers.
“Grade 3 requested local adverse reactions were reported more frequently after Dose 2 than after Dose 1,” says Moderna’s statement. Grade 3 adverse reactions include swelling, pain, body aches, headache and fever.
But why?
Analogies always help. Imagine that you look out the window one night and see someone sneaking out. He looks scary, and you may be a little alarmed, but don’t panic.
“The first time someone sees that spy from Tom, they can be very scared. They can go to the police station and report that person and someone will do an outline and that will go to all police stations,” said evolutionary biology professor Michael Worobey of the University of Arizona.
A few weeks later, you hear a noise, look out the window and see the same face. You are more likely to react strongly this time, knowing that you have seen this face before. Your heart is pounding, your hands are moist, and your mind is racing. You can even call 911. And the police will be ready to pick up the guy.
“The next time that person tries to do something, there is likely to be a much bigger response, because there are more people who are familiar with that face now,” explains Worobey.
The first dose of the vaccine is like that first look at the stranger – the body’s immune system perceives and takes some care, but the second time it is even more prepared to recognize and respond to that request.
That’s how vaccines work in general, of course. They were meant to be like a wanted poster, educating the immune system to stay alert.
So-called booster vaccines – those that work best with two or more doses – prolong that response.
“With the first dose, you have to generate an immune response from scratch,” said Worobey.
The body makes antibodies, but it also begins to generate immune cells called B cells to make targeted antibodies. This takes time – a process known as ripening.
“You end up with a perfectly adjusted B cell population,” said Worobey. “So, the second time you give a person a shot, these cells stay still like an army of clones and can immediately start producing a great immune response, which is what happens when people feel they have been kicked in the teeth. “
Thomas Geisbert, professor and specialist in emerging viral threats at the University of Texas Medical Branch, notes that some vaccines generate a lot of response with a single dose. But the initial momentum strategy builds a more lasting defense force, he says.
“Your immune system is already boosted with the first dose,” he said. So, with a second dose, “you tend to develop a longer and more durable response”.
Flu-like symptoms that accompany any viral infection are not caused by the virus itself. They are caused by the body’s response. Fever and muscle aches come from inflammation, which in turn is a signal that immune cells called T cells are giving off an alarm in the form of signaling chemicals called cytokines.
“You get swelling at the injection site,” said Geisbert. “People may have chills or pain, or they may be passed out or tired.”
This bodes well for predicting whether vaccines will provide better protection than natural immunity. “These symptoms mean that your immune system is speeding up and the vaccine is really working,” said Dr. Rochelle Walensky, director of the United States’ Center for Disease Control and Prevention, in an interview at the White House last month.
The new coronavirus has only been around for a year, so no one can say yet whether it will be more like measles, which people get once in their lives, or the flu, which people get repeatedly.
Studies indicate that coronavirus immunity lasts for months anyway – six months, nine months or even longer.
This is not 100% of the population – immunity varies widely from person to person, and some cases have been documented of people being infected twice with the coronavirus. But they seem to be unusual cases.
These studies also take pictures of people’s immune systems over time and show that, right after infection, two types of antibodies increase in number and then fall off, while a third type accumulates more slowly. And then the B cells that have been “trained” to recognize the virus begin to produce specific antibodies that accumulate in the blood.
Vaccination can speed up this process – providing people with faster protection, but also providing a broader level of protection than a natural infection would.
“As everything is happening so fast, studies and key data have not yet arrived,” said Geisbert.