Wearing masks, practicing social distancing, and washing hands are effective methods for preventing transmission, but the development of safe and effective vaccines is currently one of the primary ways to achieve herd immunity quickly. By the end of 2020, some vaccines were in use around the world, and there are currently over 40 vaccines in clinical trials, with others still in preclinical stages. This article will explore what we need to know about COVID-19 vaccines.

1. What vaccines are currently used in the United States?
As of January 2021, there are two types of vaccines approved in the United States, which have begun initial vaccinations for emergency medical personnel and the elderly to prevent COVID-19.
(1) Pfizer-BioNTech vaccine (mRNA vaccine BNT162b2). The Pfizer vaccine is suitable for individuals aged 16 and older and is administered in two doses three weeks apart.
(2) Moderna vaccine (mRNA 1273). The Moderna vaccine is suitable for individuals aged 18 and older and is administered in two doses four weeks apart.

2. How do these vaccines work and how effective are they?
The currently available vaccines are based on a type of genetic material called ribonucleic acid (RNA). When the vaccine is administered, it uses proteins to induce an immune response. mRNA, or messenger RNA, does not penetrate the cell nucleus and therefore does not alter DNA. The vaccine is delivered through a carrier system called lipid nanoparticles, which produce the spike protein found on the surface of the coronavirus. This protein prevents the virus from attaching to cells. In the case of the Pfizer vaccine, it showed 95% effectiveness in preventing early-stage COVID-19 seven days or more after the second dose. For the Moderna vaccine, large-scale phase 3 trials indicated a 94.1% effectiveness in preventing COVID-19 fourteen days or more after the second dose.

3. What types of trials do vaccines undergo?
Vaccines go through a preclinical stage followed by three phases of clinical trials. In the United States, the Food and Drug Administration (FDA) must approve each stage before moving on to the next. In the preclinical stage, the vaccine is tested on small animals. However, for the coronavirus vaccine, experiments were conducted on primates at this stage. If no toxic side effects are observed and an immune response is demonstrated, the vaccine moves to phase 1 clinical trials. This phase tests the safety of the experimental vaccine, typically involving fewer than 100 healthy individuals. Phase 1 trials also assess the appropriate dosage. If successful, the vaccine progresses to phase 2 clinical trials, which are larger in scale and test the vaccine's safety more rigorously. Phase 3 clinical trials evaluate whether the vaccine prevents infection and does not pose specific risks. In these trials, a placebo is randomly administered to some participants to create a control group.

4. Can pregnant or reproductive-age women receive the vaccine?
The American College of Obstetrics and Gynecology recently stated that pregnant or breastfeeding individuals among high-risk healthcare workers should not postpone COVID-19 vaccination. However, due to the lack of long-term data on vaccines for pregnant individuals, their decision to decline vaccination should be respected. This does not imply that the vaccine is unsafe. mRNA vaccines do not inject the actual virus and do not penetrate the cell nucleus, so they do not cause genetic mutations.

5. Can children under 16 receive the vaccine?
Currently, there is no experimental data for children and infants, so it is not possible to determine whether vaccination is safe for those under 16.

6. What are the side effects of the vaccine? In what cases is vaccine use prohibited?
Some side effects of the vaccine are common symptoms seen with other vaccines. These include pain, swelling, and redness at the injection site, as well as fever, fatigue, headache, and body aches. If a severe allergic reaction occurs after the first dose, the second dose should not be administered.

7. When can vaccinations be received?
Vaccines are currently categorized by eligibility in phases. It is advisable to register with local government or hospitals to receive updates on when vaccinations can be administered. You can refer to the table below to check which phase you belong to.

References:
https://www.cdc.gov/vaccines/covid-19/info-by-product/clinical-considerations.html
https://www.acog.org/clinical/clinical-guidance/practice-advisory/articles/2020/12/vaccinating-pregnant-and-lactating-patients-against-covid-19

Data from: ACIP COVID-19 Vaccine Working Group. Phased Allocation of COVID-19 Vaccines. Available at: 
https://www.cdc.gov/vaccines/acip/meetings/downloads/slides-2020-12/slides-12-20/02-COVID-Dooling.pdf

Written by Jennifer E Cho, MD FACOG