MIT Medical answers your COVID-19 questions. Got a question about COVID-19? Send it to us at CovidQ@mit.edu, and we’ll do our best to provide an answer.
I’m obese. I’m 70 years old. I recently got the J&J vaccine and experienced no side effects at all, not even a sore arm. I know that some people, especially in my age group, often have no side effects from vaccinations. But I’ve also heard that obese people often do not gain immune response from vaccination. Can I take some kind of antibody test to see if I have protection against COVID-19?
You are not the only one asking this question. After more than a year of taking extreme precautions to prevent the spread of COVID-19, many of us are responding to the CDC’s increasingly relaxed guidelines for fully vaccinated people with a simultaneous mix of exhilaration and terror.
We know the facts: All three currently approved vaccines have been shown to be highly effective at preventing symptomatic illness. They are close to 100 percent effective when it comes to preventing hospitalization and death. But we still hear about occasional breakthrough cases — fully vaccinated people who, nonetheless, have gotten sick from COVID-19.
How worried should we be? As of April 26, 2021, the CDC reports 9,245 cases of individuals diagnosed with COVID-19 after vaccination. We’ll do the math for you: that’s roughly 0.01 percent or approximately one in 10,000 of the more than 95 million individuals who were fully vaccinated as of that date. To be clear, the CDC acknowledges that this number is a vast undercount due to under-reporting and the fact that mild and asymptomatic infections are unlikely to be detected. Because the vaccines are so good at preventing symptomatic illness, asymptomatic or very mild infections are likely to be caught only if vaccinated people are regularly tested, as they are at MIT. Still, it’s abundantly clear that the vast majority of fully vaccinated people are well protected against moderate to severe illness.
Now, let’s take a closer look at your specific concerns:
But I didn’t have any side effects.
Public-health communicators have done a great job at informing people that vaccination side effects, like soreness at the injection site and flu-like symptoms, are normal signs of a robust immune response and not cause for concern. We haven’t done as well at making sure people know that lack of side effects does not equal lack of immune response.
“So many factors influence how an individual will react to any vaccine,” emphasizes Associate Medical Director Shawn Ferullo. “These include general health, genetics, age, gender, medications you regularly take, and — in the case of the COVID-19 vaccine — whether or not you’ve been previously infected with the virus.”
In fact, a significant number of participants in clinical trials for all three currently approved COVID-19 vaccines — Pfizer, Moderna, and J&J — experienced no systemic reactions at all. But the data showed that they were just as likely to be protected against the virus as participants who did have side effects.
As you note, older participants were less likely than younger participants to experience vaccine side effects. “But,” says Ferullo, “vaccines were shown to be highly effective in the older group. Older individuals might not have quite as strong an immune response as those in the under-65 group, but vaccine effectiveness is not significantly different.”
But I’ve heard the vaccines often don’t work in people who are obese.
We have good news for you on that front. Despite early speculation that COVID-19 vaccinations would not be effective in individuals with obesity, the data tell a different story. In clinical trials, no vaccine showed a significant difference in efficacy for people who are obese versus those who are not.
A report on the two mRNA vaccines, published in April, notes that the Pfizer vaccine was shown to have 95.4% efficacy in people with obesity compared to 94.8% in people without (from seven days after the second dose). In the Moderna trial, vaccine efficacy (from 14 days after the second dose) was 94.1% overall and 91.2% in the subgroup with severe obesity. The J&J clinical trials showed a similar lack of difference in vaccine efficacy between individuals with or without obesity. In more than 10,000 subjects with obesity, the overall efficacy vaccine efficacy was 66% after 28 days. For non-obese participants, it was a statistically indistinguishable 69%.
In other words, all available scientific evidence suggests that your vaccine is almost certainly working.
But should I take an antibody test just to be sure?
There’s evidence that vaccines may not be effective for individuals with compromised immune systems. Among others, this would include transplant recipients, blood-cancer patients, and individuals taking immunosuppressant drugs to treat conditions such as rheumatic or musculoskeletal diseases. Such individuals should still get vaccinated — the COVID-19 vaccine is safe for this group — but they might want to discuss post-vaccination testing with their healthcare providers.
But even for immunocompromised individuals, the CDC generally recommends against antibody testing.
There are a number of reasons for this. The first is that not all antibody tests detect the spike protein antibodies triggered by vaccination. And even tests that look for the right kind of antibodies usually don’t distinguish between “binding antibodies,” which simply attach themselves to the virus to summon an immune response, and “neutralizing antibodies,” which can directly inactivate the virus by blocking it from entering and infecting the body’s cells. Many research studies (including clinical trials for COVID-19 vaccines) have utilized neutralizing antibody tests, but commercial versions of these tests may be difficult to find.
Even if you find the right kind of test, there’s the problem of figuring out what your results might mean. While quantitative antibody tests can provide a numerical value that pinpoints exactly how many neutralizing antibodies you have, we still don’t know how antibody level correlates with immunity against this particular virus. In other words, your antibody level, no matter how precisely measured, won’t tell you how well protected you are.
Finally, it’s important to remember that antibodies are not the whole story. Antibodies may be the first line of defense against a viral infection, but T cells, which remember viruses and guard against reinfection, may be even more important. Vaccination is likely to generate substantial T-cell immunity, but this type of protection is more difficult to measure and is completely unrelated to results on an antibody test.
Vaccination protects communities, not just individuals. While your vaccine is probably working for you, it’s important to remember that vaccination has a purpose beyond protecting the individual vaccine recipient. While experts believe that the SARS-CoV-2 virus is unlikely to be eradicated completely, we already have evidence that mass vaccination can slow transmission to the point where most members of the community are protected. And that would include those whose individual immune response to vaccination may be less than optimal.
The vast majority of vaccinated individuals, like you, have protected themselves from becoming ill with COVID-19. But a growing body of evidence also suggests that fully vaccinated people are less likely to transmit the SARS-CoV-2 virus to others. This breaks the chain of transmission and limits potential outbreaks, which, in turn, increases protection for every member of the community. Each additional vaccinated person adds to the strength of this community-level protection.
By getting vaccinated, you’ve helped to protect yourself and those around you. Now that you’ve done your part to limit the spread of COVID-19, we encourage you to spread something else instead: Information.
These safe, effective vaccines are the best way we have to stop the virus. So please tell everyone you know! Encourage your family, friends, and acquaintances to get the vaccine. Maybe even help to make vaccine appointments for the people you care about. Tell them about your experience with the vaccine, and let them know that side effects are possible but not guaranteed. Sore arm or not, you’ve done the best thing you can possibly do to protect yourself and others from COVID-19.