Will there be an Omicron-specific vaccine?
In December 2021, Anthony Fauci, MD, director of the National Institute of Allergy and Infectious Diseases, asserted that there was no need for a variant-specific vaccine and that the current booster regimen was adequate.
Recent Centers for Disease Control and Prevention (CDC) studies support that statement. One study found that third or booster doses of either the Pfizer or Moderna vaccines, both mRNA vaccines, were 90% effective in preventing hospitalizations in December and January, when Omicron was already the main variant. Stopping these vaccines after two doses was only 57% effective for preventing hospitalizations, by comparison.
The Omicron variant now accounts for more than 99% of new COVID cases in the United States. Both Pfizer and Moderna are in the process of developing vaccines that will target this specific strain. Pfizer just launched a clinical trial to assess the safety and effectiveness of its version.
Carrie Horn, MD, chief medical officer and chief of the Division of Hospital & Internal Medicine at National Jewish Health, suggests that developing Omicron-specific vaccines is a good test run to improve our ability to make rapid changes, but cautions that the virus continues to mutate.
“I would say it is a little bit of a risk because you don’t know what variant will be prevalent by March and afterwards, and that could impact if this vaccine will add more benefit than the current version,” she said. “But it is good that people are working on ways to adjust the vaccine to give real time protection if we find that current vaccines become less effective.”
Who is currently eligible for a “fourth dose” of COVID-19 vaccine?
The fourth dose booster shot is ONLY recommended for those who are moderately or severely immunocompromised.
Currently, recommendations call for immunocompromised adults to receive the standard first and second doses of mRNA vaccines (Pfizer or Moderna) followed by a third primary dose. The fourth dose booster shot is also recommended for those who are moderately or severely immunocompromised. This recommendation was extended in January to also include children who are immunocompromised and also reduces the time for the mRNA booster shot from six to three months.
The addition of the fourth dose was welcome news for many as, according to the CDC, this group encompasses about 7 million adults who are at higher risk of contracting severe disease and developing long-COVID.
The immunocompromised is a broad classification that includes anyone whose immune system has been weakened (e.g., organ transplant recipients and people with autoimmune diseases). For this population, there is a chance that the vaccine did not create as robust of an immune response as it has in the majority of individuals. Additionally, this group was in the early groups to get the initial vaccine series and third dose, which could now be showing waning antibody levels. The United States now joins countries like Chile, Denmark, Belgium and Israel as among the first to allow fourth shots to vulnerable populations.
Dr. Horn agrees with this decision. “I think there could be significant benefit for that population, as they seem to have responded better to the vaccine with every subsequent dose,” she said. “And by providing the booster a month earlier, just as their antibody levels start to wane, and Omicron infections are still so widespread, it could make a big difference.”
Again, for those who are not immunocompromised, no fourth dose is recommended at this time. As always, people should follow their own doctor’s advice when it comes to additional shots.
When could the general population expect to be allowed to get a fourth dose?
With the virus in flux and new data forthcoming, there are too many unknowns to speculate. Dr. Horn suspects the vaccine could be approved for frontline workers in the next few months, and could then become available to the general population sometime after that.
This type of staggered approach would follow a similar timeline to what we have already experienced. The original Pfizer vaccine received emergency use authorization on December 11, 2020, beginning a gradual rollout that prioritized health care workers and the immunocompromised. By mid-April 2021, all U.S. adults nationwide were eligible to receive vaccines.
Is a combination COVID/flu vaccine an option yet?
Although Moderna has announced it is working on a COVID/flu combo vaccine, it likely won’t be ready for some time. The company’s CEO recently cited a targeted release date of the fall of 2023. Patients can, however, usually receive both a flu shot and a COVID vaccine now in the same sitting.
If I am immunocompromised, when should I get a fourth dose?
Immunocompromised people have been able to receive a third primary dose of an mRNA vaccine 28 days after their second shot. They can now receive a booster three months later, since the CDC recently shortened their recommendation. The CDC did not alter its recommendation for when immunocompromised people could receive boosters for the Johnson and Johnson vaccine, which remains at two months after their last dose.
Currently, fourth doses are only recommended for those who are immunocompromised. We do recommend that anyone eligible should receive a booster shot to increase the effectiveness of their initial vaccinations.
For those who are moderately or severely immunocompromised, fourth doses of mRNA vaccine are recommended as follows:
| Who? |
What? |
When? |
| |
First Dose (Primary) |
Second Dose (Primary) |
Third Dose (Additional Primary) |
Fourth Dose (Booster)* |
| Immunocompromised People age 5+ |
Pfizer |
ASAP |
21 days after first dose |
28 days after second dose |
3 months after third dose if age 12+ |
| Immunocompromised People age 18+ |
Moderna |
ASAP |
28 days after first dose |
28 days after second dose |
3 months after third dose |
| Immunocompromised People age 18+ |
Johnson & Johnson |
ASAP |
None |
None |
2 months after first dose |
*All doses in the primary vaccine series should be the same, but either Pfizer (age 12+) or Moderna (age 18+) mRNA vaccine is suggested for the booster dose in most cases, including for those who received Johnson & Johnson. Source: CDC
What is the difference between a booster and an additional primary shot? What is a fourth dose?
The distinction between the two depends on the type of vaccine. In the case of the Pfizer vaccine, there is no difference from dose to dose other than the recommended timing. For the Moderna vaccine, Dr. Horn said the booster would be half the dosage amount of the initial dose of the primary series.
How effective is the fourth dose?
Experts like Dr. Horn believe in its value. “If the endpoint is to prevent severe illness, hospitalization and death, it works well,” she said. “You will still have the early neutralizing response to minimize the virus’s ability to replicate in your body.”
Will another booster be needed after a fourth?
Maximum COVID protection remains a moving target. Researchers are examining data on vaccine effectiveness and defensive longevity to determine next steps. Some speculate that COVID vaccination will become an annual ritual, especially given the virus’s tendency to mutate into more transmissible variants.
The scientific community’s understanding of the virus-vaccine dynamic tends to mutate, too, and recommendations may not always be one-size fits all. Different populations will require different treatments.
Final thoughts
New treatments for COVID, like monoclonal antibodies, are becoming more available, but vaccines are key right now.
“They are still the most important way to stay safe. I would say if you haven’t been vaccinated yet, please do so and speak to your doctor about whether the fourth dose is right for you,” Dr. Horn said. “And continue to wear masks, wash your hands and social distance to keep yourselves and others healthy and avoid overwhelming the health care system.”