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Vaccines Q & A

Q&A: Will vaccinated people need booster doses?

As the Delta virus variant continues to spread, experts have been discussing the possible need for booster doses for those who have been vaccinated. Pfizer is now seeking emergency use authorization from U.S. regulators to distribute a booster shot developed for its COVID-19 vaccine. Few experts are advocating for boosters while more than half of the U.S. population remains unvaccinated.

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Authors:
William Moss, Executive Director
July 12, 2021

“Americans who have been fully vaccinated against COVID-19 do not need a booster shot at this time. FDA, CDC, and NIH are engaged in a science-based, rigorous process to consider whether or when a booster might be necessary,” the U.S. Centers for Disease Control and Prevention and the Food and Drug Administration said in a recent joint statement. “Virtually all COVID-19 hospitalizations and deaths are among those who are unvaccinated. We encourage Americans who have not yet been vaccinated to get vaccinated as soon as possible to protect themselves and their community.”

Will booster shots be required, or will that depend on the original vaccine?

There is no need or recommendation for booster doses for people who are fully immunized in the United States. This will be a decision by the FDA and CDC with input from the Advisory Committee on Immunization Practices. These are the expert groups that will make the decision when and for whom booster doses are needed.

There are two reasons why we might need booster doses. One would be if we see waning immunity and a loss of protection over time from the original vaccine. But we haven’t seen evidence of that yet.

The other reason would be the threat that new variants could escape the immunity conferred by vaccines. There is some evidence of slight decreases in protective efficacy, but the current portfolio of vaccines is very effective against severe disease, hospitalization, and death. I don’t foresee a need for booster doses in the near future for the Pfizer and Moderna vaccines. But it’s possible that some people, such as those who are immunosuppressed at the time of vaccination or the elderly, may require booster doses earlier than the general population.

‘There is no need or recommendation for booster doses for people who are fully immunized in the United States.’

The bottom line for people to take away is that the currently authorized vaccines in the United States remain highly protective against severe disease due to all of the known variants and particularly the Delta variant.

Why does Pfizer believe booster doses may be needed?

Pfizer is drawing this conclusion, in part, based on some recent data presented by Israel’s ministry of health showing the efficacy of the Pfizer vaccine decline from about 90% to 64%. It’s unclear how generalizable that is. There are other studies suggesting that the protective effectiveness remains high – maybe a little lower than what was seen in the Phase III trials against earlier variants. But certainly, it remains high against severe disease. We’re just going to need to monitor this.

Pfizer did say that it has evidence that a third dose of the Pfizer vaccine really boosts antibody responses and that they’ll be seeking emergency use authorization and that they are working on vaccines that specifically target the Delta variant, as is Moderna.

Can mixing different vaccines strengthen immunity?

There is evidence that mixed vaccine regimens can be very immunogenic, particularly when looking at various combinations of the Pfizer and AstraZeneca vaccines.

Early reports of individuals who got the AstraZeneca first and Pfizer second had very strong immune responses with high antibody levels. So, it looks like that combination of vaccines could be very worthwhile.

Has the CDC offered any guidance about boosters?

The CDC has not come out with recommendations on booster doses, and specifically for people who have gotten the single-shot J&J vaccine. I think they do need to come out with some kind of statement soon even in the absence of evidence, particularly for those who received a single dose of the J&J vaccine. People are asking the question and are going forward with getting booster doses with mRNA vaccines.

We know that the J&J vaccine was less effective against the Beta variant in South Africa than other vaccines. We know that the AstraZeneca and Pfizer vaccines are slightly less effective in protecting against symptomatic disease due to the Delta variant when given as two doses and markedly less effective with just one dose. That at least raises some concern about the J&J vaccine and the Delta variant. We know that with another adenovirus vaccine – the AstraZeneca one – that you get a very strong immune response when boosted with Pfizer.

‘We need to focus on increasing vaccination coverage in the United States not on strategies for developing boosters for those already vaccinated’

Thus, there is circumstantial evidence that at least raises a very legitimate question about whether people who got the J&J vaccine should get a booster dose with the mRNA vaccines.

Now, Johnson & Johnson recently announced new laboratory data based on a small number of blood samples that showed its single-shot vaccine generated neutralizing antibodies against the Delta and other variants, up to at least eight months. So, hopefully booster doses will not be necessary to protect against disease due to the Delta variant.

The National Institutes of Health is funding a study looking at mixing Moderna, Pfizer, and Johnson & Johnson vaccines with a booster dose of the Moderna vaccine.

How would you determine who needs a booster shot if they got one dose of the J&J vaccine?

If a person who got a single dose of J&J is living in a community with high vaccine coverage and where case counts are low, it would be prudent for that individual to wait for more evidence or recommendations from the CDC.

However, in the absence of better data, if the person with a single shot J&J vaccine lives in a community with low vaccination coverage and where the number of cases is increasing due to the Delta variant – it would be reasonable for that person to take a couple of steps. First, they should be practicing common sense public health measures such as masking and avoiding crowded areas. Second, it might be prudent to get a second dose with an mRNA vaccine knowing that there is no evidence supporting that and there are no CDC recommendations for it.

Would the Novavax vaccine be deployed as a booster?

Novavax could play an important role in boosters when and if we need them.

Novavax could also play a role in encouraging more people to get vaccinated. I’ve heard anecdotally that people may be more likely to get vaccinated with Novavax because they’re not comfortable with the mRNA vaccines, which are a new vaccine technology although they have been in development for two decades. I don’t know if that is going to really move the needle in terms of convincing more people to get vaccinated, but it’s possible.

Novavax is a more traditional vaccine platform. Instead of providing the genetic recipe for our own cells to make the spike protein, which is done with the mRNA and adenovirus vector vaccines, it simply injects the protein itself along with something that stimulates our immune system. There are many examples of this type of vaccine that people are more familiar with, such as the tetanus and diphtheria vaccines. They inject a protein that the immune system identifies and then develops an immune response to.

‘Novavax could also play a role in encouraging more people to get vaccinated.’

What was striking and remarkable was the overall high 90% efficacy that we have seen with the Novavax vaccine. It’s slightly lower than what we’ve seen with the mRNA vaccines, but higher than the adenovirus vector vaccines. There was also high protective efficacy in high-risk adults and some of the variants of interest and concern. We don’t know how it will perform against Delta but there was somewhat decreased efficacy against the Beta variant.

On the global scale we need every vaccine we can get. With such a high efficacy vaccine that doesn’t require extremely cold temperatures to store and ship it, Novavax could be a major benefit to getting more vaccines to other countries.

William Moss, Executive Director

William Moss, MD, MPH, is Executive Director of the International Vaccine Access Center, Johns Hopkins Bloomberg School of Public Health.