(CNN) You finally got your coronavirus vaccine. It took weeks, maybe a few calls, before driving through the jackpot with a vaccination clinic. Or maybe you’re a health worker who got the chance to work.
Now comes the hard part – make sure you get the second dose on time. This means another appointment and keep a close eye on the calendar. Plus, maybe, a little anxiety.
Doctors have warned people that the first dose may give them a chance. And now people are starting to report that the second dose can cause more side effects than the first dose.
This is not an unexpected finding. Moderna and Pfizer both said in their submissions to the U.S. Food and Drug Administration that there was a noticeable difference in the responses to the doses when they tested their vaccinations with volunteers.
“Grade 3 required local adverse reactions to dose 2 as dose 1,” reads the statement from Moderna. Grade 3 side effects include swelling, aches, body aches, headaches and fever.
But why?
Analogies always help. Imagine looking out the window one night and seeing someone sneaking around. He looks whimsical, and you may be a little scared, but you do not panic.
“The first time someone sees that squeaking Tom, they can be pretty crawled out. They can go to the police station and report this person, and someone will draw a sketch and it goes to all the police stations,” says Michael Worobey, professor of evolutionary biology, from the University of Arizona.
A few weeks later you hear a sound, look out the window and see the same face. It is likely that you will react more strongly this time, knowing that you have already seen this face. Your heart beats, your hands get damp and your mind rushes. You can even call 911.. And the police will be ready to come and grab the guy.
“The next time the person tries to do something, there will probably be a much bigger reaction because there are more people who know the face now,” Worobey explains.
The first dose of vaccine is like the first look at the stranger – the body’s immune system takes notice and takes some precautions, but the second time it’s even better to recognize and respond to the indication.
This, of course, is how vaccines work in general. They are meant to be like a popular poster, educating the immune system to be on the lookout.
So-called prime boost vaccines – those that work better with two or more doses – trigger this reaction.
“With the first dose, you need to generate an immune response from the ground up,” Worobey said.
The body produces antibodies, but also begins to generate immune cells called B cells to form antibodies. It takes time – a process known as aging.
“You have a fine B-cell population,” Worobey said. “Then, the second time you give a person a chance, those cells sit like a clone army and can immediately start giving them a very big immune response, this is what happens when people feel they have been kicked in the teeth.”
Thomas Geisbert, a professor and expert on emerging viral threats at the University of Texas’ medical branch, notes that some vaccines build a lot of response with a single dose. But the strategy for the first boost builds a long-lasting army, he says.
“Your immune system has been stagnant since the first dose,” he said. So with a second dose, “You tend to build a longer and more lasting response.”
The flu-like symptoms of viral infections are not caused by the virus itself. It is caused by the body’s reaction. The fever and muscle aches come from inflammation, which in turn is a sign that immune cells called T cells are sending out an alarm in the form of signaling chemicals called cytokines.
“You get swelling at the injection site,” Geisbert said. “People may have colds or aches, or they may feel down or feel tired.”
It is good to predict whether the vaccines provide better protection than natural immunity. “These symptoms mean that your immune system is recovering and that the vaccine is actually working,” said Dr. Rochelle Walensky, director of the American Center for Disease Control and Prevention, said at an information session in the White House last month.
The new coronavirus only exists for about a year, so no one can say yet whether it will be more like measles that people catch once in a lifetime, or like flu that people catch again and again.
Studies suggest that immunity to coronavirus lasts months anyway – six months, nine months or even longer.
It is not 100% of the population – immunity varies greatly from person to person, and some cases have been documented to infect humans twice with coronavirus. But they seem to be unusual cases.
These studies also take snapshots of people’s immune systems over time and show that two types of antibodies, just after infection, grow in number and then collapse, while a third type builds up more slowly. And then B cells that are ‘trained’ to recognize the virus begin to produce specific antibodies that build up in the blood.
Vaccination can speed up this process – it provides people with faster protection, but may also provide a broader level of protection than a natural infection would do.
“Because it’s all going so fast, the studies and the most important data are not there yet,” Geisbert said.