Suggestions for timing vaccines towards respiratory viruses
August 29, 2025
6 min learn
Yearly, viral respiratory infections place a major burden on the well being care system.
The CDC predicts that influenza, respiratory syncytial virus and COVID-19 collectively will account for 27.3 million to 47.7 million outpatient visits, 1.1 million to 2.1 million hospitalizations and 73,000 to 207,000 deaths in the USA between October 2024 and September 2025, with direct and oblique prices within the billions of {dollars}.
Fortuitously, a number of vaccines can be found for these infections, in addition to monoclonal antibody merchandise (clesrovimab, nirsevimab) which give infants with passive immunity towards RSV. The CDC recommends annual influenza vaccination for all sufferers aged 6 months or older and a single dose of RSV vaccine for older adults and pregnant girls at 32 to 36 weeks’ gestation.
Suggestions for COVID-19 vaccination proceed to evolve, with some separation now between the CDC and different teams.
For example, the American Academy of Pediatrics recommends routine COVID-19 vaccination for infants aged 6 to 23 months, youngsters aged 2 to 18 years in sure danger teams, and pregnant adolescents. Each the AAP and CDC advocate COVID-19 vaccination for any baby aged 6 months or older who’s reasonably or severely immunocompromised, however past that, the CDC’s suggestions name for shared scientific decision-making.
Moreover, the AAP and American Faculty of Obstetricians and Gynecologists proceed to advocate COVID-19 vaccination in being pregnant, breaking with federal suggestions introduced earlier this 12 months.
For influenza and RSV, ACIP suggestions recommend fall as one of the best time to manage vaccines. Understanding the interaction between virus seasonality and immune response can assist clinicians additional optimize the timing and administration of those vaccines to maximise their protecting results towards respiratory sicknesses.
A cautious stability
Maybe the only most vital driver of vaccine timing for respiratory infections is the seasonality of respiratory viruses. Within the continental U.S., the seasonal patterns of influenza and RSV are well-described, typically beginning in October and lasting via April of the next 12 months, with peaks from December to February. As SARS-CoV-2 transitions to an endemic virus, it is usually anticipated to show seasonality. Present forecasts recommend both an annual peak within the winter or a big winter peak with smaller peaks in spring and summer season are the almost definitely seasonal patterns of COVID-19 sickness. With information of those temporal tendencies in viral respiratory infections, clinicians can guarantee sufferers are vaccinated previous to intervals of biggest virus circulation and transmission.
Maximizing vaccine safety requires alignment of those viral seasonal patterns with the temporal course of vaccine immune response. Vaccines must be administered with enough time to permit impact earlier than virus publicity happens. Immune response to vaccination usually develops by 14 days; for influenza, RSV and COVID-19, vaccines have demonstrated antibody response inside 2 to 4 weeks of administration.
Nonetheless, not all vaccines exhibit sturdy responses. In recent times, quite a few research have demonstrated waning efficacy of influenza vaccines each between seasons and inside a single season. In a meta-analysis of 14 research of influenza vaccine effectiveness, Younger and colleagues discovered that vaccine effectiveness decreased by 33% 3 to six months after vaccination. Presently accessible COVID-19 vaccines have additionally demonstrated waning effectiveness, with decreases of 21% to 38% by 6 months after vaccination, though waning immunity might have been exacerbated by mutations in circulating strains of SARS-CoV-2. As a result of they’ve solely been in the marketplace since 2023, much less is understood concerning the sturdiness of RSV vaccines; nevertheless, presently accessible knowledge point out these vaccines preserve safety via at the very least two seasons.
Given the stress between time to vaccine response and sturdiness, clinicians should rigorously stability the necessity for early administration towards offering enough length of safety.
Sadly, there may be little passable proof to information a extra exact timing of administration for these vaccines. Amongst influenza, RSV and COVID-19 vaccines, influenza vaccination is greatest studied.
In a well being state transition mannequin, Ferdinands and colleagues evaluated the tradeoffs of various influenza vaccine timing eventualities in contrast with precise immunization charges and timing noticed within the U.S. in 2012-2013. Of their mannequin, delaying all vaccination till October elevated influenza hospitalizations in most eventualities, as did considerably growing the variety of people vaccinated in August and September. Nonetheless, the precise outcomes for every state of affairs assorted considerably primarily based on assumptions concerning the timing of influenza season, vaccine effectiveness, and the way shortly effectiveness waned. In distinction, a separate examine by Newall and colleagues utilizing various modeling approaches instructed that the optimum begin time for influenza vaccine rollout was in September, with late September most well-liked for sufferers extra possible so see fast waning of effectiveness (for instance, older adults and people with compromised immunity).
Comparable modeling research haven’t but been carried out for RSV or COVID-19 vaccines. Nonetheless, one latest paper on maternal RSV vaccination discovered that administration greater than 5 weeks earlier than supply resulted in larger placental antibody switch, and a separate examine of maternal RSV vaccination discovered it had the best scientific utility at avoiding RSV-associated hospitalizations amongst infants when administered to pregnant girls between September and December. Vaccination was most cost-effective when administered to pregnant girls between September and November. These knowledge, although restricted, present some hints for clinicians about methods to doubtlessly optimize timing for influenza and maternal RSV vaccines.
Position of antigenic drift
A closing consideration concerning immune response and the timing of respiratory virus vaccines is the position of antigenic drift. As talked about above, mutations in COVID-19 possible amplified the waning of vaccine efficacy over time. Such mutations in circulating viruses, even within the absence of waning vaccine effectiveness, can necessitate repeat vaccination with reformulated merchandise.
This antigenic drift is well-described with influenza and is one other main cause why annual vaccination is important for this virus. The same strategy to COVID-19 vaccination could also be helpful. In a latest examine of ensemble-based projections of COVID-19 sicknesses, an annual COVID-19 vaccination program utilizing formulations matched to circulating variants was projected to stop 431,000 hospitalizations and 49,000 deaths within the U.S.
Conversely, RSV doesn’t show important antigenic drift, so the necessity for added vaccinations will possible be pushed by length of immune response fairly than viral mutations, and proposals on repeat vaccination are prone to change as extra is discovered concerning the sturdiness of RSV immunity.
Ultimate timing?
Taken collectively, these knowledge point out that by selling respiratory virus vaccines within the early fall, clinicians can leverage seasonality and immune dynamics to optimize vaccine timing to yield the best vaccine effectiveness.
As COVID-19 continues to transition to an endemic an infection, a technique of annual influenza and COVID-19 vaccination in September might maximize the advantages of vaccination for these infections. For older adults, it’s unclear if RSV vaccination will ultimately require multiple dose, however given the overlapping timing of RSV, influenza and doubtlessly COVID-19 seasons, September administration of RSV vaccine to unvaccinated people is probably going an inexpensive strategy.
These vaccines will be safely co-administered, so a single appointment in September for annual influenza, COVID-19, and probably bi- or triennial RSV vaccines could also be a handy possibility for sufferers to obtain these vaccines on the proper time. For pregnant girls, selling RSV vaccination nearer to 32 weeks’ gestation throughout RSV season might maximize vaccine effectiveness. Nonetheless, in all eventualities, vaccination at any indicated time is most well-liked to no vaccination, so particular person preferences and circumstances may even have to be thought of.
In abstract, via understanding the dynamics of seasonality and immunity, clinicians can develop a extra nuanced plan for when to manage respiratory virus vaccinations. Influenza and RSV share overlapping seasons, and COVID-19 is anticipated to do the identical. To maximise effectiveness through the respiratory virus season, fall administration of those vaccines is suitable. Till extra proof is out there, co-administration of advisable respiratory virus vaccines in September might characterize a super technique for optimizing the timing of those vaccines.
References:
- Bonanni P, et al. Infect Dis Ther. 2025;doi:10.1007/s40121-025-01135-0.
- CDC. Immunization schedules. https://www.cdc.gov/vaccines/hcp/imz-schedules/index.html. Up to date Could 29, 2025. Accessed August 14, 2025.
- CDC. Preliminary estimated flu illness burden 2024-2025 flu season. https://www.cdc.gov/flu-burden/php/data-vis/2024-2025.html. Printed Could 9, 2025. Accessed Aug. 13, 2025.
- CDC. Preliminary estimates of COVID-19 burden for 2024-2025. https://www.cdc.gov/covid/php/surveillance/burden-estimates.html. Printed Dec. 6, 2024. Accessed Aug. 13, 2025.
- CDC. Preliminary Estimates of RSV Burden for 2024-2025. https://www.cdc.gov/rsv/php/surveillance/burden-estimates.html. Printed July 8, 2025. Accessed Aug. 13, 2025.
- Ferdinands JM, et al. Clin Infect Dis. 2020;doi:10.1093/cid/ciz452.
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- Moriyama M, at al. Annu Rev Virol. 2020;doi:10.1146/annurev-virology-012420-022445.
- Menegale F, et al. JAMA Netw Open. 2023;doi:10.1001/jamanetworkopen.2023.10650.
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- Younger B, et al. J Infect Dis. 2018;doi:10.1093/infdis/jix632.
For extra data:
Gregory B. Tallman, PharmD, MS, BCPS, BCIDP, is a scientific pharmacy specialist in infectious ailments and program director of the PGY2 infectious ailments pharmacy residency at Windfall St. Joseph Well being. He will be reached at gregory.tallman@windfall.org.
