In the three months since the omicron variant emerged, its toll across the globe has been devastating. In the United States, the average daily deaths due to omicron have already exceeded those during the delta variant’s peak last September, according to the New York Times COVID-19 data tracker. Confirmed infections have far surpassed last winter’s surge, and record hospitalizations have further strained overwhelmed hospitals.
But amid the devastation, experts have found reason for hope. Though unvaccinated people remain vulnerable to omicron, those who are vaccinated have proven to be well protected.
AAMCNews spoke with five experts in infectious disease and vaccines to answer some of the most common questions about omicron and the COVID-19 vaccines.
Is the primary series of a COVID-19 vaccine effective against omicron?
“The simplest answer would be [the vaccines] are holding very well in terms of protecting from severe disease and hospitalization and worse,” says Alessandro Sette, Dr.Biol.Sci, an immunologist and professor at La Jolla Institute for Immunology in California. “[But] they are not holding as well at protection from infection.”
In December, when omicron became the dominant variant in the United States, unvaccinated adults age 18 and older were hospitalized at a rate 16 times higher than adults who had completed at least their primary series of a COVID-19 vaccine (one shot of the Johnson & Johnson vaccine or two shots of the Pfizer or Moderna vaccine), according to data from the Centers for Disease Control and Prevention (CDC). In people over the age of 50, the hospitalization rate was 18 times higher for unvaccinated people.
Even so, omicron has reduced the effectiveness of the vaccines against both hospitalization and infection, particularly among people who received one shot of the Johnson & Johnson vaccine and people who were vaccinated five or more months ago. This is because the protective antibodies that can quickly identify and destroy the first sign of the virus in the body wane over time. Furthermore, the 36 mutations to omicron’s spike protein — which all three of the vaccines target — have made antibodies somewhat less able to neutralize the virus.
“In the omicron era, one might want to think about requiring a booster to be considered fully vaccinated. … We know you will do better with three [shots] than with two.”
Sten Vermund, MD, PhD
Infectious disease epidemiologist, dean, and professor at the Yale School of Public Health and Yale School of Medicine in New Haven, Connecticut
While this does mean that more people are likely to get infected and may experience symptoms, they are still far less likely to experience the worst outcomes that have been associated with the virus in unvaccinated people. This is because the body can also activate a molecular immune response with what are called T cells.
“There are two types of immune response: the neutralizing antibodies [and] cellular immunity,” Sette explains. “The neutralizing antibodies neutralize the virus … playing a major role in preventing infection. However, if the virus gets through … the T-cells have amazing capacity to recognize infected cells — recognize fragments of virus decorating the surface of the cell — they know that the cell is infected, and they kill it.”
Do I need a booster shot?
Studies show that booster shots significantly reduce the likelihood of hospitalization and infection.
“In the omicron era, one might want to think about requiring a booster to be considered fully vaccinated,” says Sten Vermund, MD, PhD, an infectious disease epidemiologist, dean, and professor at the Yale School of Public Health and Yale School of Medicine in New Haven, Connecticut. “We know you will do better with three [shots] than with two.”
A booster dose can increase effectiveness against hospitalization from between 60% and 70% for the primary series to about 90%, according to Wilbur Chen, MD, an infectious disease physician-scientist and professor at the University of Maryland School of Medicine in Baltimore. It does so by reactivating the immune system to create more antibodies, which tend to wane in the months following the primary series.
The CDC is now recommending that anyone age 12 or older who received their second dose of the Pfizer or Moderna vaccine five or more months ago, or who received a single dose of the Johnson & Johnson vaccine two or more months ago, should get a booster from either Pfizer or Moderna. Studies have shown that mixing vaccine brands is safe and can provide robust protection.
Can vaccinated people transmit the virus?
They can, but there is evidence that they do so less than unvaccinated people do.
“The day after a vaccinated person might get infected, there may be a lot of virus in your nose. In the next day, your immune system has kicked in quickly, thanks to the vaccine-induced memory,” Vermund says. “You’re infectious for a shorter period of time if you are vaccinated and your peak viral load is less in the nasopharynx.”
“Making sure that you wear a well-fitting mask is important whether you’re boosted or not.”
Wilbur Chen, MD
Infectious disease physician-scientist and professor at the University of Maryland School of Medicine in Baltimore
Does this mean that vaccinated people don’t need to wear masks? Not exactly. Omicron is super infectious, and about 20% of people in the United States over the age of 5 — as well as all children under 5 — remain unvaccinated. They, as well as vaccinated people who are immunocompromised and at higher risk of severe COVID-19, are still vulnerable to being infected by a vaccinated person.
“Making sure that you wear a well-fitting mask is important whether you’re boosted or not,” Chen explains. “Irrespective of your vaccination status, masking is an important part of the message.”
What if I’m vaccinated and catch COVID-19? Did the vaccines fail?
Even if a vaccinated person becomes infected and has symptoms of COVID-19, it does not mean the vaccines are not working. If the infection does not cause hospitalization or death, many vaccine experts say that the vaccine has been successful.
“No vaccines prevent any and all infection,” says E. John Wherry, PhD, director of the Penn Institute for Immunology at the Perelman School of Medicine at the University of Pennsylvania in Philadelphia. “We have to set our bar appropriately.”
The good news is that vaccinated people who become infected and recover may have the best immunity against future infection.
“[With] infection followed by vaccination or vice versa, you get a broader immune response,” says Anna Durbin, MD, a professor at Johns Hopkins University School of Medicine and Johns Hopkins Bloomberg School of Public Health in Baltimore who specializes in infectious disease and vaccines. “We expect we’ll see good protection against omicron for at least three months or longer, based on antibody titers induced by booster shots.”
Will I need more boosters?
Probably. The remaining questions are: When will you need them, and what kind of vaccine should they be?
Durbin says it’s not best practice to continue adding boosters of the existing vaccines as they become less effective against emerging variants.
“It makes more sense to make a second-generation vaccine with a sequence more in line with delta or omicron,” she says. “That will broaden your immune response.”
Pfizer and Moderna announced in January that they are testing booster shots that are specifically targeted to omicron, but Sette notes that by the time they are ready for the public, other variants may have become dominant.
“I’m hoping that we’ll have enough immunity through vaccination and infection or combination of both that … there’s enough population immunity that we’re not going to see hospitals overwhelmed.”
Anna Durbin, MD
Professor at Johns Hopkins University School of Medicine and Johns Hopkins Bloomberg School of Public Health in Baltimore
In parallel, he believes it’s prudent to develop vaccines that target multiple variants — as is done with the annual flu vaccine — or that target different parts of the virus besides the spike protein.
The timing of booster doses is also important, Durbin adds, explaining that the immune system should have a chance to return to its baseline before an additional shot in order to maximize its response.
In the meantime, experts are hopeful that, as the omicron wave recedes, much of the population will have a good level of immunity at least for a few months.
“I’m hoping that we’ll have enough immunity through vaccination and infection or combination of both that … there’s enough population immunity that we’re not going to see hospitals overwhelmed,” Durbin says.
This is assuming that no new and more deadly variant emerges. Broad vaccination across the globe will be needed to prevent the emergence and spread of even more dangerous variants.
“It is in our raw self-interest to vaccinate the world,” Vermund says. “The fewer people who have rip-roaring virus replication, the fewer variants will be produced. It will be beneficial to everyone if people around the world can be vaccinated against COVID-19.”