A guide to who can safely get the Pfizer/BioNTech Covid-19 vaccine

With the first doses of Covid-19 vaccine being administered across the United States, questions abound about who can safely get them.

Expect answers to those questions to evolve as the vaccines go into broader use. But here’s what is known so far, and what experts at or advising the Centers for Disease Control and Prevention recommend regarding their use at this point.

Pregnant people

The Covid vaccine developed by Pfizer and its partner, BioNTech, hasn’t yet been tested in pregnant people — in fact none of the vaccines in development have been. Drug and vaccine makers are always reluctant to include pregnant people in clinical initial trials for fear of injuring a developing fetus or threatening a pregnancy.

For now, the CDC’s assessment is that pregnant people should be offered a chance to get the vaccine, but should informed it hasn’t yet been tested in the population. (Britain’s Joint Committee on Vaccination and Immunization took a different approach, advising against giving the vaccine to pregnant people.)

During last Saturday’s meeting of the Advisory Committee on Immunization Practices — an expert group that advises the CDC — a Pfizer executive said there were no safety concerns raised in the preliminary data from animal studies conducted to see if the company’s vaccine could pose a risk to developing fetuses. This type of animal study, called a developmental and reproductive toxicity trial, is a prerequisite to testing the vaccine in pregnant people.

Lactating people

To date the vaccine’s safety in those who are lactating hasn’t been studied. So there are no data on which to advise whether they should be vaccinated.

On the other hand, messenger RNA vaccines — the Pfizer and Moderna vaccines are both mRNA vaccines — are not thought to pose a risk to a breastfeeding infant, the CDC said, indicating that if those who are lactating are in a priority group eligible for vaccination, they can choose to be vaccinated if they wish.

People with allergies

Reports that two nurses in Britain developed anaphylaxis after being immunized with the Pfizer vaccine last week triggered concerns about whether people with allergies should be vaccinated. Both the women had serious allergies and carried EpiPens.

The CDC’s clinical guidance, which the agency posted to its website on Monday, is broken down into three categories — proceed with vaccination, vaccinate with caution, and don’t vaccinate.

People who have allergies to foods, animals, insects, latex, and other common allergies can be vaccinated. Likewise, people with allergies to oral drugs, even if they are the oral equivalent to an injectable drug, can take the vaccine, the CDC guidance said. Included in this group are people who have had a non-serious allergic reaction to an injection — though not anaphylaxis — and people who have a family history of anaphylaxis, but who have not experienced it themselves.

People who have had a severe allergic reaction to a vaccine or an injectable therapy can be vaccinated, but with caution. These people should undergo a risk assessment with their care provider.

People who have a severe allergic reaction to a dose of this vaccine should not receive another dose, the Food and Drug Administration’s fact sheet on the vaccine said. And people who have a history of a severe allergic reaction to any of the components of the Pfizer vaccine should not be vaccinated with it, the CDC guidance said.

The vaccine consists of messenger RNA and four lipid nanoparticles; there are no preservatives in the vaccine. In a call with physicians on Sunday, a CDC scientist said people could be allergic to a part of the lipid nanoparticle known as polyethylene glycol, or PEG, which is a component in other injectable medicines. A detailed list of the ingredients in the vaccine is on page 2 of the FDA fact sheet linked to above.

Children and teens younger than 16

The Pfizer vaccine was authorized for use in people 16 years of age and older. While the company is now studying its use in adolescents aged 12 to 15, data from that work were not part of the company’s application to the FDA for an emergency use authorization. So for now, the vaccine isn’t authorized for use in anyone below the age of 16.

Studies in children 11 and under will require what’s known as dose de-escalation — figuring out how much vaccine is appropriate and tolerated in younger children. That work hasn’t started yet.

People with HIV

Pfizer enrolled some HIV-positive volunteers with stable infections in its Phase 2/3 clinical trial, but there are not enough data to date to do an analysis of this population.

The CDC said people with HIV can be vaccinated, but should be counseled that the safety and efficacy of the vaccine in immunocompromised people is still unclear and they should continue to take other measures to protect themselves against infection.

People on immunosuppressant therapy

People who take drugs to suppress their immune systems — organ recipients, for instance — can be vaccinated as long as they don’t have another condition for which vaccination is not advised.

People who have recently received or plan to soon receive another vaccination

Co-administration of vaccines is common, and a useful tool for vaccine delivery. It’s easier to give someone two shots at once than to ask them to come in twice. If it turns out people need regular Covid vaccine boosters, for instance, it’s likely they would be administered when people get their flu shots.

But in order to be sure vaccines can be co-administered without undermining the effectiveness of any of the vaccines, studies need to be conducted, and there hasn’t been time. So for now the CDC is recommending that people not get any other vaccinations in the two weeks before or two weeks after getting a Covid vaccine.

That said, if someone inadvertently gets the Pfizer vaccine less than two weeks after getting another immunization, they do not need to repeat either vaccination, the CDC said.

People who got the Pfizer vaccine for their first Covid-19 shot

Anyone who gets a first dose of the Pfizer vaccine needs to get the Pfizer vaccine for their second shot 21 days later. (Actually, the shot can be given within a 17-day to 21-day window.)

The same will be true of the Moderna vaccine, which will likely receive an emergency use authorization later this week.

At some point in time, research may show Covid vaccines can be used interchangeably. But until the issue is studied, the vaccines need to be used as authorized. No getting the Pfizer vaccine for the first dose and the Moderna the second, or vice versa.

— This article has been updated to include information on the ingredients in the Pfizer vaccine.