The Johnson & Johnson vaccine requires only one dose, but the Pfizer/BioNTech and Moderna vaccines require two doses. Some people have reported stronger side effects after their second doses, according to both Pfizer and Moderna. Those side effects are indicators of the immune system responding properly.
The reason for two doses is to create a strong immunity. “With the first dose, you are having to generate an immune response from the ground up,” said Michael Worobey, an evolutionary biology professor at the University of Arizona. The body produces antibodies, but also starts to generate immune cells called B cells to make targeted antibodies — and that takes time, Worobey said. “Then the second time you give a person the shot, those cells are sitting around like a clone army and can immediately start producing a very big immune response, which is what is happening when people feel like they have been kicked in the teeth.”
Some vaccines build up plenty of response with a single dose, said professor Thomas Geisbert, an expert in emerging viral threats at the University of Texas Medical Branch. But the second dose in two-dose vaccines builds a longer-lasting defense force.
Missing the second vaccine should not be considered as it takes away increased protection provided by the second dose, and may also reduce the time span of your protection.
“Your immune system is already jacked up from the first dose,” Geisbert said. So with a second dose, “you tend to build up a longer and more durable response.”
“You can take these medications to relieve post-vaccination side effects if you have no other medical reasons that prevent you from taking these medications normally,” the CDC said.
The second dose is not recommended if you take over-the-counter medications, such as ibuprofen, aspirin, or acetaminophen. “It is not known how these medications might affect how well the vaccine works,” the agency said. “However, if you take these medications regularly for other reasons, you should keep taking them before you get vaccinated. It is also not recommended to take antihistamines before getting a COVID-19 vaccine to try to prevent allergic reactions.”
If the side effect symptoms seem severe, linger for more than a few days or the site of injection gets increasingly tender or red, contact your doctor or health care provider.
If there’s a chance for side effects, do young, healthy adults really need to get vaccinated?
There are plenty of reasons why young, healthy people should get a Covid-19 vaccine: A dangerous, highly contagious new variant is affecting young people. “In the Upper Midwest, we’re starting to see lots of younger adults getting sick and going to the hospital from Covid because of the B.1.1.7 variant,” Hotez said. “So remember that the B.1.1.7 variant is different from past types of Covid infections that we’ve seen — more serious and possibly more severe disease among younger people.”