Covid-19 vaccines may cause mild side effects, experts say, stressing need for education, not alarm

While the world awaits the results of large clinical trials of Covid-19 vaccines, experts say the data so far suggest one important possibility: The vaccines may carry a bit of a kick.

In vaccine parlance, they appear to be “reactogenic,” meaning they have induced short-term discomfort in a percentage of the people who have received them in clinical trials. This kind of discomfort includes headache, sore arms, fatigue, chills, and fever.

As long as the side effects of eventual Covid-19 vaccines are transient and not severe, these would not be sources of alarm — in fact, they may be signals of an immune system lurching into gear. It’s a simple fact that some vaccines are more unpleasant to take than others. Think about the pain of a tetanus shot, for instance.

But experts say it makes sense to prepare people now for the possibility that Covid-19 vaccines may be reactogenic.

“I think one of the things we’re going to have to realize is that all of these vaccines are going to be reactogenic…. They’re all going to be associated with reactions,” said Kathryn Edwards, scientific director of the Vanderbilt Vaccine Research Program in Nashville, Tenn.

“I think if you were to point out that, look, this is going to be a little bit painful, but there’s an end to it, and there’s a greater good to be gained here, I think that that’s probably worthwhile,” agreed Brian Southwell, senior director of the science in the public sphere program at the Center for Communication Science at RTI International, a think tank located in Research Triangle Park, N.C.

At least two manufacturers, Cambridge, Mass.-based Moderna and CanSino, a Chinese vaccine maker, stopped testing the highest doses of their Covid-19 vaccines because of the number of severe adverse events recorded among participants in their clinical trials.

Ian Haydon, one of the volunteers who received the highest dose in the Moderna Phase 1 clinical trial, ended up seeking medical care after he spiked a fever of 103 Fahrenheit 12 hours after getting a second dose of the vaccine. (Most Covid-19 vaccines will likely require two doses to work.)

The side effects are being seen across a number of different vaccines, made in different ways. This does not appear to be a problem linked to a specific type of Covid-19 vaccine.

The Oxford University-AstraZeneca vaccine, which uses a harmless-to-humans virus that infects chimpanzees as its backbone, saw adverse events reported by 60% of recipients in its early phase trial, reported last week in the journal The Lancet. Half of patients who got the highest dose of the Pfizer-BioNTech vaccine — which like Moderna’s is a messenger RNA vaccine — reported side effects.

Even after abandoning study of its highest dose, CanSino saw nearly three-quarters of the people in the vaccine arms in its Phase 2 trial report side effects, though none was severe. The CanSino vaccine uses a human adenovirus as its backbone.

Getting people prepared for the fact that the Covid-19 vaccines may be reactogenic lets them know what to expect when vaccine becomes available, said Kathleen Neuzil, director of the Center for Vaccine Development at the University of Maryland School of Medicine.

“As with many vaccines, we have found that if we let people know what to expect, then they have fewer concerns if side effects happen,” Neuzil said.

There’s plenty of evidence that people will accept reactogenic vaccines — will virtually rush to get them — if they are concerned enough about the condition the vaccine is designed to prevent.

Edwards said GSK’s shingles vaccine, Shingrix, which reportedly makes people feel pretty miserable for a short period after injection, is a perfect example. Despite the possibility of discomfort, from the moment the vaccine was brought to market, the company could not keep up with the crush of demand for it. (GSK recently announced the vaccine was no longer in short supply.)

Most people know someone who has had shingles; they’ve heard how painful the condition — a reactivation of latent varicella virus, a late side-effect of chickenpox infection — is for people who develop it.

But the behavior of many Americans suggests they don’t see Covid-19 as a particular threat, with many resisting wearing masks and following the social distancing recommendations that have successfully driven down transmission in a number of other parts of the world.

A variety of polls suggest between half and 70% of Americans plan to be vaccinated when Covid-19 vaccines become available, figures that raise concerns in some quarters about the ability of vaccines to trigger herd immunity in the U.S. population.

Noel Brewer, a professor of health behavior at the University of North Carolina, isn’t worried at this point about those polling numbers. At present, it’s not even clear if vaccines will work, he said, which means pollsters are asking people about hypothetical decisions they may have to make at some unknown point in the future.

“It’s all just a bunch of question marks,” said Brewer, who actually thinks the polling numbers look pretty good under the circumstances. “Once folks are faced with a specific vaccine and a particular effectiveness profile and so on, they can then make a decision based on a thing, as opposed to an idea of a thing.”

For most people right now, Covid-19 is invisible “unless you are in an ICU,” he said. “For most of us every day, we don’t see people who are really sick.”

Brewer, who is on a World Health Organization subcommittee on Covid-19 vaccine safety, said people do expect some discomfort from getting vaccinated.

“The real question is: How much discomfort compared to what other things they may be facing? So, if you’re 70 years old and you can’t leave your house at all, you’re going to have one calculus as compared to if you’re someone who’s 20 years old,” he said.

Conditions at the time vaccine becomes ready for use will be a big influencing factor when the public is offered vaccines, said Southwell. In the meantime, though, he thinks it is critical to communicate with the public about issues like how vaccines are made and that the Covid-19 vaccines may be reactogenic.

People are paying attention to these issues, he said, arguing that members of public has a greater capacity to understand than they are generally given credit for.

“There might be a much greater case for acceptance if we do our work in building trust now and laying the groundwork now,” said Southwell. “But we’re not necessarily as focused on that as we could be.”