Recently, many people have been reaching out with questions about vaccines. So, I thought it would be helpful to mention some of the most common ones and try to provide some answers.

-- Are there sound medical reasons to oppose vaccination?

There can be, but vaccines typically provide a path towards individual protection and herd immunity that involves less burden and risk than becoming infected with a disease. Today's childhood vaccination schedule protects against more than a dozen different diseases. Some individuals, though, may need to decline vaccines if they have a compromised immune system or an allergy to one of the ingredients. When a vaccine is determined to be safe and effective, it will often make sense for healthy individuals to choose, on their own initiative, to get immunized.

-- Are vaccines safe?

The safety profile of vaccines is typically verified by extensive clinical trials involving more than 30,000 participants. Even after successful safety testing, children or adults can develop symptoms or problems, apparently from an inoculation they received. When the problem is further investigated, it may turn out to be a separate health issue unrelated to vaccination. Still, vaccines are not a zero-risk proposal, and on rare occasions, adverse events do occur. No medical intervention is ever completely risk-free. The risk of complications or side effects from vaccines, being reasonably low overall, can be deemed acceptable when compared to the prospect of complications that may arise from the disease itself. For generations, some of those complications included family members living in an iron lung after being ravaged by polio, married individuals rendered infertile from mumps, and infants dying due to whooping cough. Recent generations have been shielded from these types of devastating outcomes through the availability of vaccines.

-- Are there ethical reasons not to receive vaccines?

Certain concerns of conscience arise when cell lines derived from abortions are used in the development and production of vaccines. Vaccines should not be manufactured in this way, and pharmaceutical companies should not make use of these fetal cell lines. The Vatican's Congregation for the Doctrine of the Faith has noted, however, that when vaccines have been produced this way, it is morally permissible to receive them. When equivalent alternative vaccines that don't rely on such cell lines are available, however, those should clearly be the preferred option.

-- Why wouldn't it be wrong to receive a vaccine made from aborted fetal cell lines?

No moral evil is committed by those who get inoculated with vaccines made from problematic cell lines; rather those who originally exploited aborted children for their cells, or established pharmaceutical company policies that rely on the abortion-derived cells, commit moral evils. The one receiving the vaccine has no causal connection to these wrongful decisions made previously by others, and the end user cannot be held culpable for their wrongdoing. Even so, the Vatican emphasizes that when we receive vaccines manufactured in this way, we should take steps to register our disagreement and call on pharmaceutical companies to reformulate their vaccines using alternative and ethically acceptable cell sources. Fortunately, none of the 2020-2021 flu vaccines use aborted fetal material, a common concern as the winter season draws near. However, even if they did, it would be ethically permissible to receive the vaccine as an end user, as explained.

-- If a vaccine for COVID-19 becomes available, would we be obliged as Christians and as citizens to take it to defeat the spread of the virus?

Each person must evaluate his or her individual situation and make a good prudential judgment regarding the benefit-to-burden ratio when accepting a COVID-19 vaccine. For example, health care workers who have not been exposed to COVID-19 should seriously consider the benefits of getting vaccinated, and their workplace may even require it. The elderly and other vulnerable populations should carefully consider the benefits as well. For younger individuals with very low chances of detrimental outcomes there may be less urgency, particularly if they do not have any contact with vulnerable populations. Governments should not compel citizens to accept COVID-19 vaccinations, but rather inform them of the benefits and risks while encouraging them to carefully decide for themselves.

-- What about the new technologies behind RNA vaccines which have never been used before in humans?

The criteria for vaccine safety and efficacy are generally well-established and won't differ fundamentally for a COVID-19 RNA vaccine when compared to other more standard types of vaccines. In light of the various studies that have already been done in animals, and presupposing rigorous human clinical trials, it should soon become clear whether mRNA vaccines are as safe and effective as other vaccines.

These kinds of questions about vaccinations and human health merit attention, as they manifest an important desire both for sound scientific information and ethical clarity.

- Father Tadeusz Pacholczyk, Ph.D. earned his doctorate in neuroscience from Yale and did post-doctoral work at Harvard. He is a priest of the diocese of Fall River and serves as the Director of Education at The National Catholic Bioethics Center in Philadelphia,