CNN  — 

Pfizer and BioNTech announced Tuesday that they’re beginning a clinical trial for an Omicron-specific Covid-19 vaccine, and Moderna revealed Wednesday that it has entered Phase 2 of its own trial of a vaccine that targets the variant, which is by far the dominant one in the United States right now.

About 50% of eligible Americans have received a booster shot, according to the US Centers for Disease Control and Prevention, but the Pfizer and Moderna news might raise questions regardless. For those who have yet to get inoculated, should they wait until there is an Omicron-specific vaccine? What if someone has already had Covid-19 during the Omicron surge, do they still need a booster? And what does this mean for people who’ve already gotten a booster, or those who received the one-dose Johnson & Johnson vaccine and then subsequently got a dose of another kind?

For answers to these and other questions, I spoke with CNN Medical Analyst Dr. Leana Wen. Wen is an emergency physician and professor of health policy and management at the George Washington University Milken Institute School of Public Health. She is also author of “Lifelines: A Doctor’s Journey in the Fight for Public Health.”

CNN: Should people hold off on getting their booster until they can receive an Omicron-specific one?

Dr. Leana Wen: No, they shouldn’t. Everyone eligible to receive a booster should do so now.

Here are two key reasons why: First, there is growing evidence that a third shot of Pfizer or Moderna or a second vaccine following Johnson & Johnson is needed to sustain strong protection against Covid-19. Last week, three large new studies from the CDC found that boosters protect against severe illness and reduce the likelihood of contracting coronavirus.

During a period in December and January when Omicron was dominant, one study found that getting a booster dose was 90% effective at preventing hospitalization, compared with the 57% effectiveness seen in vaccinated people who had not been boosted and were six months past their second shot. Another study examining over 13,000 Omicron cases found that the likelihood of developing symptomatic infection was 66% lower in participants with three doses compared with two.

Second, the Omicron-specific vaccines are still in clinical trials. The trials will take months complete. We don’t know yet the results of the trial and whether these variant-specific vaccines will be better than the original vaccines. Even if they end up getting authorized, it will be months from now, and with Omicron still surging, people shouldn’t delay their boosters.

If you are an adult at least five months out from your two doses of Pfizer or Moderna, or two months out from your one dose of Johnson & Johnson, you should get a booster now. Adolescents 12 and older are also recommended to receive a third dose of the Pfizer vaccine if it’s been at least five months since their second dose (only the Pfizer/BioNtech vaccine is authorized for adolescents 12 to 17).

CNN: If you get the regular booster now, does that mean you can’t get the Omicron-specific booster later?

Wen: No. One of the groups Pfizer is studying includes individuals who received three doses and now are receiving a fourth vaccine dose that is an Omicron-specific booster. The company will be studying the effect of this fourth dose. It may be that a fourth shot isn’t needed because the initial booster will continue to provide very good protection. But if the variant-specific booster, in addition to the third dose, is something that adds a lot more protection, the recommendation may well be that people receive it in the future.

CNN: What if someone has just had Omicron? Should they still get the regular booster now?

Wen: Most people don’t find out what variant of Covid-19 they had if they were infected, but given that Omicron now constitutes over 99% of new infections, if they recently contracted the coronavirus, it probably was Omicron.

Individuals who are vaccinated and also recovered from infection appear to have a very high degree of immune protection. The immunity from recovery is variable, though. Someone who became very ill may have a stronger antibody response compared with someone who had an asymptomatic infection, and we don’t know how long that immunity lasts.

That’s why boosters are still recommended for people who have had Covid-19. They can receive one as soon as their isolation period ends, as long as they no longer have a fever and their symptoms are improving.

CNN: How long does the booster last? Do you think we will need a second booster soon?

Wen: We don’t know. A new pre-print study from the University of Texas, online but not yet peer-reviewed, found that antibodies against Omicron remain robust four months after the booster dose. There are also other components of the immune response, T-cells and B-cells, that may remain strong for months, too, but we just don’t know yet when immunity after three shots may wane. This is something that researchers will monitor very carefully. In the meantime, the evidence is very clear that people need to receive that booster dose.

CNN: What about people who initially received the Johnson & Johnson vaccine, and then subsequently got their booster? Do they need a third shot?

Wen: I’m one of these people – I initially received the one-dose Johnson & Johnson vaccine in a clinical trial and then decided to “mix and match” and got a Pfizer booster.

I don’t think those of us who have received a second dose of any of the vaccines (Pfizer, Moderna or J&J) following the initial J&J shot need to receive a third shot at this time. A study out of South Africa found that a second dose of J&J was 85% effective against hospitalization during a time when Omicron was circulating, compared with 63% after one dose. Another real-world study from the United Kingdom looked at the AstraZeneca vaccine, which is similar to J&J.

It found that while two doses of AstraZeneca provided little protection against Omicron, a Pfizer booster following AstraZeneca resulted in 71% protection against symptomatic illness. This was a similar level of protection to those who received three doses of the Pfizer vaccine.

At the moment, the recommendation is that those of us in the US who received J&J initially are fine with a second dose of any of the three authorized vaccines. I am not planning to get a third vaccine dose any time soon. However, I do think there’s been a sense that federal health guidance has lagged for J&J recipients, and I hope there will not be a delay in advising us should research come out that a third dose is needed.

CNN: Do you think the development of Omicron-specific vaccines will help with speeding up the end of the pandemic?

Wen: I am optimistic, in general, about the Covid-19 pandemic coming to an end. Not that Covid-19 is going to disappear – it’s something that’s almost certainly going to be with us for the foreseeable future – but we have many more tools that will allow us to coexist with the virus so that it doesn’t have to dominate our lives.

Developing new vaccines will be a key part of living with Covid-19. I hope there will be more research into vaccines that target coronaviruses broadly, so that if new mutations arise, we don’t need to keep playing Whack-a-Mole.

That said, I do think it’s a good thing that companies are developing variant-specific vaccines, especially if they end up providing better, more robust protection. Again, though, we won’t know whether that’s the case for months, and people should really not delay getting their boosters now.

This story has been updated to include additional information about Moderna’s clinical trials.