COVID-19 Vaccine Information

Q: How effective are the Pfizer and Moderna vaccines?

Segreti: Both vaccines showed around 95% effectiveness, which means that in the placebo-controlled trial, 95% of those who got COVID-19 received the placebo; only 5% of those who received the vaccine got COVID-19. The Pfizer trial included about 44,000 volunteers, and the Moderna trial had more than 30,000.

Both vaccines require two doses: Pfizer’s 21 days apart and Moderna’s 28 days apart. And both use the same messenger RNA technology to deliver the vaccine, which is great from a production standpoint because the vaccines can be manufactured and distributed a lot more quickly.

 Q: How does the vaccine work? What is messenger RNA?

Segreti: mRNA, or messenger RNA, is a molecule that carries the information cells use to produce different proteins: Think of it as a blueprint. The vaccines harmlessly mimic the virus’ ability to trigger the body’s immune responses to infections. The Pfizer and Moderna vaccines include mRNA from the coronavirus “spike” protein — which is what enables the virus to infect cells.

 Q: Can the vaccine give you COVID-19?

Segreti: As with other vaccines, COVID-19 vaccines cannot give you the virus. They do not contain a live virus.

 Q: Are the vaccines safe?

Segreti: Both the Pfizer and Moderna vaccines seem to be very safe and most people have been able to tolerate them pretty well. Neither of their phase 3 clinical trials was discontinued or even temporarily halted due to any adverse event, and fewer than 2% of recipients of these vaccines developed severe fevers of 102.2°F to 104°F.

The independent board that conducted the interim analysis of Moderna’s huge trial found that severe side effects included fatigue in 9.7% of participants, muscle pain in 8.9%, joint pain in 5.2% and headache in 4.5%. For the Pfizer vaccine, the numbers were lower: Severe side effects included fatigue (3.8%) and headache (2%).

 Q: Will the COVID-19 vaccine be needed annually, similar to the flu vaccine?

Segreti: We don’t know yet how long the vaccine will last, so we don’t know if or how often people will need to be vaccinated again. We will make decisions about the need for future vaccinations based on what we learn going forward.

 Q: Will people who had COVID-19 already be able to get the vaccine? Do they need to get it?

Segreti: As of right now, we don’t think there’s any reason not to get vaccinated, but we will clarify that issue with the local health departments.

If you had COVID-19 and recovered from it, you probably have some antibodies to the virus that causes the disease. But we don’t entirely know what that means as far as your protection against reinfection. While we have not seen too many people get reinfected with COVID within six months of becoming sick, we don’t know how long any immunity might last. So pending guidance from the local health departments, our recommendation will likely be to get vaccinated even if you previously had COVID-19.