3 doctors explain why COVID-19 prevention doesn't stop at immunization

• Over 31 millions doses of the coronavirus vaccines have been distributed in the US as of January 31, according to the CDC.
• Doctors Syra Madad, Komal Bajaj, and Saskia Popescu explain that despite this progress, COVID-19 prevention doesn't stop at immunization.
• Immunity takes time and none of the vaccines are 100% effective, so the doctors say it's important to maintain safety precautions during this time.

Years of scientific inquiry have culminated in the development of several vaccines against SARS-CoV-2/COVID-19. Vaccines are a great and effective tool to prevent infectious disease and in the past year, we've made a tremendous achievement in developing two efficacious vaccines.

Both the Pfizer-BioNTech and Moderna vaccines have demonstrated a remarkable 94-95% efficacy at decreasing symptoms and severe COVID-19 infection.

Several other vaccines are currently in phase 3 clinical trials and preliminary data suggests promising efficacy as well.

With the availability of vaccines, conversations around herd immunity have grown, but the truth is that vaccination is merely one of many that make a holistic response to the COVID-19 pandemic.

Even after vaccination, it is important for individuals to continue infection prevention measures. These strategies include masks, social distancing, hand hygiene, and avoiding crowds/confined spaces, all of which are known to curb the spread of COVID-19 until a large portion of the population has been vaccinated.

Beyond these interventions though, there are a few other reasons why COVID-19 prevention doesn't just stop at immunization.

1. Immunity takes time

Vaccines are currently administered using a two-dose regimen several weeks apart. For the Pfizer vaccine the shots are administered three weeks apart. For Moderna, it's four weeks apart. The full protective benefits of the vaccine and for your body to develop immunity against SARS-COV-2 will take two weeks after the administration of the second dose.

Read more: I'm a radiologist in Alabama who just received the Pfizer vaccine. I've seen firsthand the serious effects of COVID-19 on people's lungs, so I had zero reservations about getting the shot.

2. The vaccine is effective, but not 100%

While the COVID-19 vaccines currently authorized for emergency use in the US reported a 94.1% (Moderna) and 95% (Pfizer) efficacy after two doses in controlled clinical trials, in the real world, the effectiveness of the vaccine may be comparable or lower given how vaccines may be stored and handled.

An efficacy of 95% means that it is anticipated 5%, or one in 20 vaccinated people, may not develop immunity and therefore, could still be susceptible to SARS-COV-2 infection. Nonetheless, an efficiency of 94% and 95%, respectively, is a remarkable achievement and on par with some of the most effective vaccines like chickenpox and measles.

3. It's unclear how long immunity lasts

Though it seems like an eternity, the COVID-19 pandemic began just over a year ago. The participants in vaccine trials will be followed to learn more about how long immunity might last.

While there's multiple variants of SARS-COV-2 circulating, vaccines are developed with mutations in mind. Researchers and public health teams keep a close eye on COVID-19 surveillance to monitor for potential variants that might impact immunity and see if changes to current vaccines or booster shots are needed but what we can do now is to continue the intervention strategies that are effective.

Read more: Moderna is seeking FDA approval to increase doses in each COVID-19 vaccine vial, reports say

4. Whether someone who has been vaccinated can still infect others is unknown

It is possible that those who have been vaccinated may still carry the virus without showing symptoms if infected, and could still be able to spread it to others. Vaccine trials largely tracked those that got sick from COVID-19, leaving open the question as to whether vaccinated individuals who didn't develop symptoms might silently spread the virus. More data is being gathered to shed further light on this complex question and while the results look promising, it's important we still take precautions to protect those around us.

Each of us plays an important role in reducing COVID-19 spread and stopping this global pandemic. One thing we can all do is to learn more about vaccines, have honest conversations about the science behind them, but also to continue following all the intervention measures - masks, great hand hygiene and social distancing - that have curbed spread.

Syra Madad, DHSc, MSc, MCP is an infectious disease epidemiologist, senior director of the system-wide special pathogens program at NYC Health + Hospitals, health and safety lead at the Enhanced Investigations Unit of NYC Test & Trace, and fellow at the Belfer Center for Science and International Affairs.

Komal Bajaj, MD, MS-HPEd is chief quality officer at NYC Health + Hospitals/Jacobi and professor at Albert Einstein College of Medicine.

Saskia Popescu, PhD, MPH, MA, CIC is an infectious disease epidemiologist and assistant professor at George Mason University.