As we continue to roll out COVID-19 vaccination here in the U.S. and, far too slowly, around the world, our next potential challenge is already looming on the horizon: the potential need for booster vaccinations. As we gather and weigh evidence on the necessity of boosters, we must not lose sight of the COVID-19 vaccine strategy that will protect us best and save the most lives.
Vaccine makers have suggested that we will need boosters and the Biden administration is they will be available if necessary. And although it is absolutely right to prepare for the possibility that we may need boosters, in reality, we if we'll need them and, if so, when. It appears that COVID-19 vaccines licensed in the U.S. provide excellent protection against mild and severe disease and against hospitalization and death, and the protection offered by both the and vaccines reportedly lasts for many months.
Determine the Right Vaccine Schedule
Different vaccines need to be given on different schedules to have the greatest protective effect. For seasonal influenza, we give a new vaccine every year because different strains of flu -- which are more genetically different from one another than current SARS-CoV-2 variants are from each other -- circulate each year, and because immunity conferred by influenza vaccines may wane rapidly.
Recommendations on when to boost vaccines may be guided by evidence on immunity generated by initial vaccine doses or by a person's risk of exposure or severe disease. We boost some vaccines if exposure has potentially occurred (e.g., tetanus) or if exposure may occur due to travel to an endemic area (e.g., typhoid) or during an outbreak (e.g., measles). We boost other vaccines if underlying medical conditions put someone at higher risk of severe disease (e.g., meningitis). In some circumstances, antibody titers may be checked to assess for evidence of immunity from prior vaccination or infection (e.g., rubella among pregnant women or hepatitis B among healthcare workers).
Gather More Data on COVID-19 Vaccines
Just as we have done for other vaccines, to establish clear guidelines for whether and when to boost, we need: a better understanding of the duration of protection against COVID-19 after vaccination; evidence on how markers of immunity change after COVID-19 vaccination over time; and robust data on how those markers correlate with protection. Levels of neutralizing antibodies against SARS-CoV-2 may decay over time, as they can after other vaccines. However, we don't know what levels of antibodies correlate with protection against COVID-19. In part, this is because it's not just antibodies that offer protection after vaccination: T cells may also offer robust, long-lasting immunity.
We will improve our understanding of post-vaccination protection by monitoring and thoroughly investigating breakthrough cases -- infections among people who have received vaccine -- over time.
A of those vaccinated against COVID-19 in the U.S. have experienced breakthrough infections, and most have had only mild symptoms. No vaccine is 100% effective; breakthrough cases are expected and are not necessarily evidence that we need boosters. However, if waning immunity results in deadly infections as time goes on, then we would need boosters, and if variants emerge against which original vaccines are less effective, we may need variant-specific boosters.
Evidence from across the globe suggests that vaccines authorized for use in the U.S. are highly protective against SARS-CoV-2 infection and severe COVID-19 caused by the new variants we are tracking, including the B.1.1.7 variant (first identified in the U.K.). A recent analysis showed that two doses of the Pfizer or AstraZeneca vaccines are highly protective against COVID-19 caused by the B.1.617.2 variant (first identified in India). Some vaccines appear to be less protective against certain variants, as suggested by from South Africa and caused by the B.1.351 variant (first identified in South Africa).
More robust studies on real-world vaccine effectiveness are needed. Data on the effectiveness of certain vaccines against some variants (in particular P.1, thought to have originated in Brazil) are lacking. Some data are from small studies and are thus of limited value for decision-making.
Focus on Vaccinating the World's Most Vulnerable
New variants emerge when there are high levels of transmission, and highly transmissible variants further accelerate disease spread. Variants spread around the world rapidly; stopping the emergence of variants will save lives here in the U.S. and globally. If we are to control transmission, we should vaccinate as many people as possible, not give booster doses of unclear necessity to some while others have yet to receive a single dose. None of us are safe until we are all safe.
Just about everyone who is hospitalized or dying from COVID-19 has one thing in common: they're unvaccinated. It's crucial that we reach those who are still unvaccinated before the virus reaches them -- and we need to protect those at highest risk first.
Make Evidence-Based Vaccine Decisions
Evidence from clinical trials and the real world -- not announcements from manufacturers at shareholder meetings -- must inform our vaccine decisions. The only basis for a decision on boosters must be scientific evidence, considered by independent panels with no conflicts of interest. We need to vaccinate widely with vaccines that are safe and effective. This applies to vaccines currently available now, and to boosters if and when needed.
The mRNA vaccine technology in particular allows us to be proactive as SARS-CoV-2 evolves. For example, Moderna has produced a that is more targeted to the B.1.351 variant and is reported to induce a good immune response against the P.1 variant; a multivalent vaccine targeted to multiple variants is being evaluated. The Johnson & Johnson vaccine offers the advantage of a single dose and has also been shown to be highly effective against B.1.351.
And mRNA vaccines are not just effective but also scalable. , but will take time. In the meantime, Americans will be most protected if vaccines are available globally. Right now, there is not nearly enough vaccine for the world, and we certainly don't have enough to vaccinate the world and also boost those who have already been vaccinated.
American taxpayers paid for the development of the Moderna, Johnson & Johnson, and other COVID-19 vaccines. These vaccines are a great insurance policy as long as we use them wisely: by expanding vaccination globally as quickly as possible to save lives and prevent the emergence of new variants. We must not lose sight of this goal as we learn more about the possible need for COVID-19 vaccine boosters.
Shama Cash-Goldwasser, MD, MPH, an infectious diseases physician and epidemiologist, is senior technical advisor on the Prevent Epidemics team at Resolve to Save Lives, an initiative of Vital Strategies.
director of the CDC during the Obama administration, is , an initiative of Vital Strategies, and at the Council on Foreign Relations.