Both the Pfizer/BioNTech and Moderna vaccines give about 95% protection against symptomatic Covid-19, and both are virtually 100% effective against severe Covid-19 illness. In their clinical trials, no one who was vaccinated died from Covid-19.
The Johnson & Johnson vaccine is not an mRNA vaccine. Among US trial participants, it was 72% effective against Covid-19 and 85% effective against severe Covid-19. Like the other two vaccines, no one who was vaccinated during the clinical trial died from Covid-19.
The Johnson & Johnson vaccine requires only one dose, but the Pfizer/BioNTech and Moderna vaccines require two doses. Some people have reported stronger covid vaccine 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 medicine, 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.”