COVID-19 vaccine: If there are no side effects, does it work?

• While many assume that side effects from a COVID-19 vaccine mean that the shot is working, researchers at Johns Hopkins in Baltimore state that people should not interpret the symptoms that way.
• The researchers found that whether one experienced side effects or not, the vaccines worked exceedingly well at generating a strong immune response.
• Overall, 99.9% of the study participants successfully developed antibodies for fighting SARS-CoV-2 infection.

Many people assume that when a person experiences side effects after COVID-19 vaccination, it is a sign that the vaccine is working.

This may leave people without such symptoms wondering whether their vaccinations have been successful. According to a new research letter from scientists at Johns Hopkins Medicine, this is not a valid concern.

The Johns Hopkins research confirmed that the Pfizer–BioNTech and Moderna vaccines are exceedingly effective at generating a strong antibody response regardless of whether a person develops side effects or not.

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The letter’s senior author Dr. Aaron Milstone, associate hospital epidemiologist at Johns Hopkins Hospital, explains,

“It wasn’t known if a lack of symptoms following vaccination or prior SARS-CoV-2 infection would indicate a less-than-adequate antibody response in people who received either the [Pfizer–BioNTech] or Moderna vaccines, so we studied an available group of staff from our hospital to see if there were any connections.”

There were none. In the study, 99.9% of all the participants successfully developed the antibodies the vaccines are designed to promote.

The research letter appears in the journal JAMA Internal Medicine.

How the mRNA vaccines work

The surface of the SARS-CoV-2 virus is covered in spikes that latch on to healthy cells, allowing the virus to enter and infect. Both of the vaccines tested — the Pfizer-BioNTech and Moderna vaccines — deliver to the body a set of instructions, or mRNA, to make the spike protein.

In response, the body’s immune system begins producing immunoglobulin G (IgG) antibodies as a defense against the spike protein. The IgG antibodies destroy and eliminate the spike protein from the body.

Should the immune system encounter SARS-CoV-2, the spikes of the virus trigger the release of these antibodies, which neutralize the virus or limit the severity of any disease it causes.

It is of note that none of the available COVID-19 vaccines contain any living or dead SARS-CoV-2.

How common were side effects?

In total, 954 healthcare workers at Johns Hopkins Medical took part in the research. All of them had received either the Pfizer or Moderna vaccines, and some had previously had a SARS-CoV-2 infection.

What indicated an infection was either having a positive SARS-CoV-2 PCR test within 14 days of the second vaccine dose or having an elevated IgG antibody count before receiving the vaccine.

The researchers asked the participants to report their reactions to their first and second inoculations. They could report none, mild — including injection site pain, headache, and mild fatigue — or clinically significant symptoms, such as fever, chills, and fatigue.

Just 5% of the participants reported side effects after their first inoculation, although 43% said that they experienced side effects after the second one.

People who took the Moderna vaccine were more likely to have clinically significant symptoms after either dose, and those who had previous SARS-CoV-2 infection were more likely to experience them after the first shot but not the second.

The vaccines did their job

Whether individuals experienced side effects or not, almost all — 953 out of 954 — developed IgG antibodies 14 days after their last vaccine dose.

The lone exception was an individual taking immunosuppressant medication.

Some people had especially high IgG levels, which the researchers link to a few possible factors. These include reporting clinically significant symptoms, being female, being under the age of 60 years, having received the Moderna vaccine, and having had earlier SARS-CoV-2 exposure.

Lead author Dr. Amanda Debes, of the Johns Hopkins Bloomberg School of Public Health in Baltimore, tells HUB, the news center for Johns Hopkins:

“The findings suggest that either spike mRNA vaccine will work well against SARS-CoV-2, even if a person doesn’t experience symptoms after vaccination or if they had a prior infection by the virus. This should help reduce anxieties that the vaccines will be less effective in either situation.”

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