Millions of people across the globe have received a COVID-19 vaccine. However, there are still numerous questions related to the effectiveness of these vaccines. One common question is whether there is a relationship between side effects observed after vaccination and subsequent immunity.

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If you have not had any side effects after a COVID-19 vaccine, are you still protected? Image credit: Mayank Makhija/NurPhoto via Getty Images

All data and statistics are based on publicly available data at the time of publication. Some information may be out of date.

There are currently 21 COVID-19 vaccines authorized for use across the globe. In the United Kingdom, over 36,500,000 people have been fully vaccinated against COVID-19 to date. In the United States, more than 162,100,000 people are now fully vaccinated.

Worldwide, over 13% of the population have been fully vaccinated against COVID-19, according to the data compiled by Google.

Real-world vaccine safety monitoring continues for all vaccines, as the Centers for Disease Control and Prevention (CDC) state. Health authorities worldwide continue to encourage those who receive a COVID-19 vaccine to report any side effects to a healthcare professional.

Millions of vaccinated people have experienced side effects, including swelling, redness, and pain at the injection site. Fever, headache, tiredness, muscle pain, chills, and nausea are also commonly reported.

As is the case with any vaccine, however, not everyone will react in the same way. Many people have not reported or experienced side effects after their vaccination. Does this mean that they are not protected against SARS-CoV-2?

Stay informed with live updates on the current COVID-19 outbreak and visit our coronavirus hub for more advice on prevention and treatment.

In an interview with Medical News Today, William Schaffner, M.D., professor of infectious diseases at Vanderbilt University Medical Center in Nashville, TN, spoke about the relationship between side effects and immunity to SARS-CoV-2, the virus that causes COVID-19.

He stated that neither the presence nor the absence of side effects indicates immunity. “There is no direct correlation between side effects and protection,” said Prof. Schaffner.

Data from the trials of the two-dose mRNA COVID-19 vaccines — Pfizer-BioNTech and Moderna — indicate that these are over 90% effective. Under 10% of those fully vaccinated may have partial to no protection.

Because of the way in which vaccines work — by prompting the body to build up immunity against the target pathogen — individuals with compromised immune systems may not be able to build up complete or even partial immunity to SARS-CoV-2.

According to Prof. Schaffner, some medications, such as immunosuppressants and some drugs used in cancer treatments, may also negatively impact the effectiveness of COVID-19 vaccines.

Some scientists have suggested that antibody testing could help assess whether a COVID-19 vaccine has promoted immunity to the new coronavirus.

However, the Food and Drug Administration (FDA) recently issued a statement saying that “antibody tests should not be used to evaluate a person’s level of immunity or protection from COVID-19 at any time, and especially after the person received a COVID-19 vaccination.”

While antibody testing may seem a reasonable way to determine whether a person has developed antibodies to SARS-CoV-2, a positive test result does not necessarily indicate that a person will not develop COVID-19.

The FDA is concerned that antibody testing could lead to a more relaxed attitude toward taking precautions against infection with the new coronavirus. This in turn could result in an increased spread of SARS-CoV-2.

Dr. Elitza S. Theel, director of the Infectious Diseases Serology Laboratory at the Mayo Clinic in Rochester, MN, responded to MNT about antibody testing.

“There is not yet an established correlate of immunity for SARS-CoV-2 like we have for other vaccine-preventable diseases,” said Dr. Theel.

“And we have to remember that the available COVID-19 serologic tests, of which there are many and can differ in their targets/performance characteristics, were not designed to indicate ‘immunity’ to reinfection but instead to indicate whether an individual has mounted an immune response to the virus or not. Whether that immune response is sufficient for long-term immunity is not something that these tests can definitively tell us at this point.”

– Dr. Elitza S. Theel

It typically takes 2 weeks following the second dose of the Pfizer-BioNTech or Moderna vaccines and 2 weeks following the single dose of Johnson & Johnson, or Janssen, vaccine for the body to build protection against SARS-CoV-2. During this time, there is still the possibility of developing COVID-19.

“The current surge in [COVID-19] cases,” Dr. Theel emphasized, “is primarily occurring in unvaccinated individuals, which is both heartbreaking and frustrating because these could have been largely prevented had those individuals opted to get vaccinated.”

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