Like most vaccines, there will probably be mild to moderate side effects of the Covid-19 vaccines. 

But experts believe the benefits of getting vaccinated outweigh potential issues if it means people are protected against the coronavirus.

“That is really critical for the general population — keeping people healthy so that they can go back to work, go back to school and so we can really reopen society in a way that we would like to,” said Yvonne Maldonado, a paediatric infectious disease epidemiologist at Stanford University.

Below, experts share some side effects that people may experience after receiving their Covid-19 vaccine.

Short-term side effects can include injection site pain, headaches and fever.

There are a number of Covid-19 vaccine candidates, but at this point, experts know the most about the Pfizer and Moderna vaccines.

“The safety of these vaccines is studied in a very rigorous way, through phase one trials, phase two and, most recently, in large phase three trials where tens of thousands of study participants received these vaccines,” said William Moss, executive director of the International Vaccine Access Center at the Johns Hopkins Bloomberg School of Public Health. 

The short-term side effects that some people experienced during the vaccine trials are in line with what is normally seen following a routine vaccination, Moss said, and these issues appeared in only about 5% to 15% of participants.

“What we know is individuals who receive these vaccines have inflammation ― the technical term for this is reactogenicity ― and this represents the body’s immune system response to the vaccine,” he said.

Post-vaccine side effects can include soreness at the site of injection, a low-grade fever, headaches, muscle aches and fatigue, Moss said. These effects can last around 12 to 36 hours after injection.

In the vaccine trials, the side effects after the second vaccine dose were stronger than after the first dose.

The Pfizer and Moderna vaccine candidates both require two doses, meaning you’ll need two shots over a short period of time to be protected. In both of their trials, there seemed to be more of a reaction after the second dose, but side effects remained mild to moderate in about 90% to 95% of cases, Maldonado said.

“In some of the studies from Moderna, about one-third of people had a fever after the second dose, and they didn’t after the first,” Maldonado said, adding that people also reported higher rates of headaches and general aches and pains after the second dose.

With the Pfizer vaccine, there was also an increased rate of headache, fever and aches and pains after the second dose. But Maldonado stressed that the reported side effects were largely mild to moderate.

In more severe cases, she said physical responses such as a fever or bad headaches could keep people out of work for a day, but that has not been common so far.

The long-term side effects still have to be studied.

The accelerated development of these vaccines and the relative newness of the coronavirus make it impossible to study long-term side effects in the present moment.

“We know about short-term side effects, and the vast majority of side effects following vaccination occur within the first 30 to 40 days,” Moss said.

The current vaccine trial participants have passed this timeline.

“There is at least a two-month follow-up in at least half of the participants. So we know a lot about the short-term side effects of these vaccines,” he said.

But understanding the long-term side effects will require additional follow-up in the months to come.

Remember that side effects are not bad — they are an expected immune response.

There is no reason for alarm if you experience any of the anticipated side effects. It’s actually a good thing ― it means your body is responding to the injections.

“Most vaccines will have some degree of minor side effects. It is, in fact, the body’s immune and inflammatory response to the vaccine,” which is supposed to happen, Maldonado said.

The nature of an immune response will involve some degree of inflammation, whether that means redness, pain at the site of injection, swelling, headaches or a low-grade fever, she said.

Moss added that side effects can be treated in part with anti-inflammatory drugs. Ultimately, the benefits of taking a Covid-19 vaccine should outweigh the discomfort.

Experts are still learning about Covid-19. The information in this story is what was known or available as of publication, but guidance can change as scientists discover more about the virus. Please check the Centers for Disease Control and Prevention for the most updated recommendations.