Medical experts from Penn State Health provide insight into vaccine development, safety, mRNA vaccines and the COVID vaccine.

• The Medical Minute: Questions answered about COVID vaccines for babies, toddlers
• The Medical Minute: Five questions answered on children and the COVID-19 vaccine
• The Medical Minute: Mammograms and the COVID-19 vaccine
• The Medical Minute: How the body responds to the COVID-19 vaccine

• U.S. Food and Drug Administration
• Centers for Disease Control and Prevention
  • V-safe After Vaccination Health Checker
  • How CDC is Making COVID-19 Vaccine Recommendations
  • Ensuring the Safety of COVID-19 Vaccines in the United States

A third dose of the Pfizer or Moderna vaccine is part of the primary vaccine series for immunocompromised individual to enhance their antibody response to COVID-19 vaccination. Immunocompromised people ages 5 and older can receive a third dose at least 28 days after their second vaccine.

In contrast, booster shots provide an increase in antibody levels because antibody levels resulting from the primary series wane after several months. 

Booster Dose #1: The U.S. Food and Drug Administration (FDA) has authorized a first booster dose for Pfizer and Moderna COVID-19 vaccines given at least five months after completion of the primary series in anyone ages 12 or older. The CDC endorsed the FDA’s decision and encourages all who are eligible to get their first booster shot, if they have not done so already.

For Johnson & Johnson’s Jansen COVID-19 vaccine, a first booster dose can be administered at least two months after the first dose of the Jansen COVID-19 vaccine to anyone over the age of 18. However, the CDC no longer recommends that people receive the Johnson & Johnson Jansen vaccine due to the risk-benefit ratio.

Booster Dose #2: The FDA has authorized a second booster dose of either the Pfizer-BioNTech or the Moderna COVID-19 vaccine for populations at higher risk for severe disease, hospitalization and death, including people ages 50 and older as well as individuals ages 12 and older who have compromised immune systems. The second booster doses can be administered at least four months after receiving the first booster dose of any COVID vaccine.

Mix-and-Match Boosters: The FDA has also authorized the use of a heterologous - “mix and match” - booster dose for the three currently available COVID-19 vaccines: Pfizer-BioNTech, Moderna and Johnson & Johnson’s Janssen COVID-19 vaccines. As an example, this means that eligible persons who initially received Johnson & Johnson’s Jansen COVID-19 vaccine may, after two months, receive a booster dose of the Pfizer, Moderna or Jansen COVID-19 vaccine.

The Centers for Disease Control and Prevention (CDC) recommends that people with moderately to severely compromised immune systems receive third doses to ensure adequate protection against COVID-19. Not only are these individuals especially vulnerable to the illness, the two-dose series of the mRNA vaccines may not provide them with the same level of protection as it does for those who are not immunocompromised. Patients can receive a third dose 28 days after their second.

Penn State Health patients may call their primary care provider’s office to schedule an appointment in their doctor’s office or another Penn State Health primary care location. Additionally, anyone eligible can visit vaccines.gov to find where they can schedule a third dose.

The Centers for Disease Control and Prevention has recommended that anyone ages 5 and older get a booster shot five months after their initial vaccination series of either the Pfizer or the Moderna vaccine. 

Previously, the U.S. Food and Drug Administration had granted emergency use authorization for booster shots for anyone age 18 and over who received the Johnson & Johnson’s COVID-19 vaccine to be administered at least two months after vaccination.

Patients should visit vaccine.gov to review eligibility for a booster shot. Penn State Health patients may call their primary care provider’s office to schedule an appointment in their doctor’s office or another Penn State Health primary care location. Additionally, anyone eligible can visit vaccines.gov to find where they can schedule a booster shot.

It’s important to know that all of the steps necessary to bring a vaccine to the public have been followed for the Food and Drug Administration (FDA) authorized and approved COVID-19 vaccines. These vaccines have undergone the most intensive safety monitoring in U.S. history - no regulatory steps were skipped. These vaccines were able to be developed so quickly because scientists had a head start due to working on vaccines against two closely related coronaviruses: SARS and MERS. Scientists had also studied how to design platforms to make a new vaccine rapidly available. For example, mRNA vaccines have been studied over several decades against other viral infections, including Zika and influenza (flu). This type of vaccine introduces a small piece of mRNA into a person’s cells which instructs the cell to make a viral protein. Their body then makes an immune response to this protein and this protects them from serious illness. The mRNA is not incorporated into a person’s DNA and is inactivated in a couple of days. The Moderna and Pfizer/BioNTech vaccines each utilize this technology.

The vaccines went through rigorous testing prior to receiving Emergency Use Authorization (EUA) from the FDA. The EUA allowed the vaccines to be disseminated rapidly to stem the pandemic while the FDA completed additional steps to fully approve the vaccines. While under EUA, rigorous safety monitoring was conducted and over 217 million people in the U.S. have now been fully vaccinated according to the Centers for Disease Control and Prevention. Significant side effects have been exceedingly rare. In pregnant women receiving the vaccine, there is no evidence for increased risk of miscarriage or harm to the fetus. Similarly, fertility is not affected by COVID-19 vaccination. The FDA approved the Pfizer vaccine on Aug, 23, 2021, and the Moderna vaccine on Jan. 31, 2022.

You can find more detailed information on the vaccines:

• Pfizer-BioNTech COVID-19 vaccine fact sheet for recipients and caregivers
• Moderna COVID-19 vaccine fact sheet for recipients and caregivers
• Single-Shot Janssen COVID-19 vaccine from Johnson & Johnson
  • *Note: The CDC no longer recommends that people receive the Johnson & Johnson Jansen vaccine due to the risk-benefit ratio.
• What to expect after getting a COVID-19 vaccine

Vaccines cause an immune response in the body which can sometimes cause flu-like symptoms such as body aches or even fever, chills and a headache. An immune response may be more likely to occur with the second dose of the Pfizer or the Moderna vaccine. Vaccinations with the Johnson & Johnson vaccine require only one dose.

Learn about the difference between a vaccine side effect and an adverse event.

See guidance from the Centers for Disease Control and Prevention about potential side effects here.

An Emergency Use Authorization, or EUA, allows the use of unapproved medical products in response to a declared public health emergency where there are no adequate, approved and available alternatives. An EUA for a COVID-19 vaccine allows vaccine distribution in the U.S. without a full FDA approval.

Studies to date indicate the COVID vaccines have high rates of effectiveness and safety among all age groups (ages 12 and older) and demographics, with a very low rate of serious side effects including in people with a variety of pre-existing health conditions. Discuss your individual health history and concerns with your primary care provider to help you make an informed decision.

Pregnancy is a known risk factor for severe COVID-19. The Centers for Disease Control and Prevention (CDC) states that women who are pregnant or were recently pregnant are more likely to get very sick from COVID-19 compared to those who are not pregnant. Additionally, women who have COVID-19 during pregnancy are at an increased risk of complications that can affect their pregnancy and developing baby. Both the CDC and the American College of Obstetricians and Gynecologists recommend that pregnant and lactating individuals be vaccinated against COVID. Clinical studies have shown that the vaccine is safe during pregnancy.

There is no data to suggest that the vaccine has an effect on fertility. The COVID vaccine is recommended for women of childbearing age. If a woman becomes pregnant after the first dose, the second dose is recommended to be given per the usual recommendations. According to the CDC, women who are trying to become pregnant do not need to avoid pregnancy after receiving an mRNA COVID-19 vaccine.  While studies are ongoing, there is no data that the COVID-19 vaccines may cause infertility and no credible scientific theories for how the COVID-19 vaccine may cause female infertility.

Per the CDC, there are no data on the safety of COVID-19 vaccines in lactating women or on the effects of mRNA vaccines on the breastfed infant or on milk production and excretion. mRNA vaccines are not thought to be a risk to the breastfeeding infant. Women who are breastfeeding may choose to be vaccinated.

The American College of Obstetricians and Gynecologists also provides guidance on COVID-19 vaccination in pregnant and lactating individuals.

The COVID-19 mRNA vaccines remain very effective at preventing hospitalization, severe disease and death, which is what they were designed to do.  However, these vaccines are less effective at preventing infection currently because the viral variant Omicron has the ability to escape from immunity developed by vaccination as well as immunity from previous infection.

New data released by the Centers for Disease Control and Prevention on Jan. 21 showed that a first booster dose of an mRNA vaccine is highly effective - 82% - at preventing COVID-19-associated emergency department and urgent care encounters and 90% effective at preventing COVID-19-associated hospitalizations. Because of these data, Penn State Health strongly recommends that everyone who is eligible for a booster should receive it as soon as possible.

The FDA has authorized a second booster dose of either the Pfizer-BioNTech or the Moderna COVID-19 vaccine for populations at higher risk for severe disease, hospitalization and death, including people ages 50 and older as well as individuals ages 12 and older who have compromised immune systems. The second booster doses can be administered at least four months after receiving the first booster dose of any COVID vaccine.

For specific data, guidance, side effects and more, please see the U.S. Food and Drug Administration’s fact sheets on the three COVID-19 vaccines:

• The Pfizer-BioNTech vaccine 
• The Moderna vaccine
• Single-Shot Janssen COVID-19 vaccine from Johnson & Johnson*

*Note: The CDC no longer recommends that people receive the Johnson & Johnson Jansen vaccine due to the risk-benefit ratio.

Studies have shown that the effectiveness of the COVID-19 vaccines does decline over time. The Centers for Disease Control and Prevention (CDC) recommends that everyone ages 18 and older to get a booster shot either five months after their initial Pfizer or Moderna series, or two months after their initial Johnson & Johnson’s Janssen vaccine. The CDC recommends that children ages 12–17 get a booster dose of the Pfizer vaccine at least five months after their initial series of vaccines. The CDC no longer recommends that people receive the Johnson & Johnson Jansen vaccine due to the risk-benefit ratio.

Natural immunity from previous infection does not protect against reinfection from the Omicron variant compared to previous viral strains.

It is recommended that those who have COVID-19 get the vaccine, including a booster, to ensure that they have a more reliable, high level of protective immunity to prevent reinfection and serious illness. You should wait to get vaccinated or boosted until you are out of isolation from COVID infection. Checking antibodies against COVID is not necessary or recommended.