It's not like delaying the selection of the strains for inclusion is a novel concept.
https://academic.oup.com/jid/article/230/1/131/7455219
DISCUSSION
Our study investigated the potential benefit of revising the current selection and formulation schedule for the next generation of influenza vaccines. We systematically assessed past influenza vaccine decisions (2012–2020), identifying 2 seasons where antigenically drifted viruses emerged postdecision, with detectable activity before the season started.
The antigenic characteristics of new variants and the timing of when new variants emerged were highly variable in the past, emphasizing the challenges faced in improving vaccine effectiveness. For example, in February of 2014, WHO recommended no change to the influenza A(H3N2) vaccine strain for 2014–2015 season, based on the observation that a majority of A(H3N2) viruses detected in the surveillance system were antigenically similar to the 2013–2014 vaccine reference virus (A/Texas/50/2012) [38]. However, antigenically drifted viruses belonging to the 3C.2a subclade began appearing in May 2014 and accounted for >80% of A(H3N2) viruses detected in the influenza vaccine effectiveness network in 2013–2014 [38, 39]. Similarly, B/Victoria viruses in 2019–2020 showed increasing diversity with emergent viruses poorly inhibited by the recommended vaccine component. [40]. These 2 seasons exemplify the case where additional data collected after February could have informed the selection of a more antigenically similar vaccine virus and improved vaccine effectiveness.
Additional samples collected close to influenza season can improve vaccine effectiveness and consequently reduce the influenza burden. The epidemiological impact of a delayed vaccine selection and production schedule depends on many factors, including the degree to which vaccine effectiveness can improve when the vaccine and circulating viruses are antigenically similar and the relative frequency of the influenza subtype or lineage during the season. Our simulation showed that updating the A(H3N2) vaccine component of the 2014–2015 season in the Northern Hemisphere could have resulted in a substantial decrease in the number of hospitalizations in the US. However, updating the B/Victoria component of the in the 2019–2020 vaccine did not yield a similar benefit, even under the assumption of greatly improved vaccine effectiveness with an antigenically more similar vaccine virus. The discrepant benefit of updating the relevant vaccine component in these 2 seasons resulted in part from the fact that A(H3N2) accounted for 83% of influenza cases in 2014–2015 whereas B/Victoria accounted for only 36.5% of influenza cases in 2019–2020 [30–36]. These results highlight the importance of improving vaccine effectiveness, especially for the subtypes or lineages that are more likely to predominate in the season, such as A(H1N1)pdm09 and A(H3N2) that have predominated the historical influenza seasons [30–36].
WHO has twice postponed selection for A(H3N2) component by 1 month—once in 2003 and again in 2019—to enable review of additional information on emergent influenza viruses [41]. Non-egg-based vaccines, with their capacity for rapid production, potentially allow more time to assess emerging influenza viruses before selecting candidate vaccine viruses. On the other hand, the proposed timeline with delayed decision on vaccine strain entails the risk of delaying the supply and delivery of influenza vaccine. The influenza vaccine supply shortage due to license suspension of a major vaccine manufacturer in 2004, for instance, underscores the need for careful examination of risks and benefits of revising vaccine formulation schedules [42]. Even after the vaccine formulation recommendation is made and vaccines are produced, the remaining steps for regulatory approval by the US Food and Drug Administration and distribution can take an additional 3–4 weeks [43]. Potential delays in availability of influenza vaccine may result in missed opportunities for vaccination, resulting in reduced vaccine uptake. Hence, the benefits of delaying strain selection need to be balanced with providing adequate and timely influenza vaccine supply.
This study quantifies the modeled impact of delaying influenza vaccine selection but acknowledges several limitations. First, the transition away from the egg-based platform, as envisioned in our study, may take a significant amount of time due to the current heavy reliance on egg-based vaccines [18]. In addition, even if the influenza surveillance period were shifted to reduce the period between decision making and the subsequent season, updating vaccine formulation would only be possible if a suitable candidate vaccine virus (CVV) were available. WHO Collaborating Centers annually identify several potential CVVs grown in both eggs and qualified mammalian cell lines. Ideally, these potential CVVs or another virus from the same genetic group are raised in ferrets and tested in hemagglutination inhibition against circulating viruses and are also used in serological assays to assess whether antibodies induced by current vaccines inhibit growth of these viruses. These processes take time and require advanced identification of a new antigenically distinct group soon after it emerges, which may not be realistic. Second, our assumption that increased antigenic similarity between vaccine and circulating viruses leads to higher vaccine effectiveness does not consider factors such as vaccine type, age, or prior vaccination status, which can influence the degree of improvements [44–46]. We varied the relative vaccine effectiveness values in our analysis to address this limitation. Additionally, we studied 2 past influenza seasons where only 1 vaccine component could have potentially been updated, offsetting its benefit by increased circulation of the other subtype or lineage of which vaccine component was not changed. However, additional surveillance data are likely to improve all vaccine components. Last, our estimation of the impact of delaying vaccine decision making is specific to US influenza epidemics. Given the hemisphere-wide nature of vaccine decisions, considering substantial heterogeneity in predominant subtypes and lineages and in the predominant clades within each subtype or lineage is crucial for a comprehensive assessment [47].
As innovative influenza vaccines emerge with the potential for improving production speed and vaccine effectiveness, the current formulation, production, and regulatory process for seasonal influenza vaccines need to be carefully reassessed. Our study investigated the potential benefit of delaying vaccine formulation decisions to enable the use of more up-to-date surveillance data, which could be feasible with next-generation vaccines. Importantly, the additional time afforded by a later decision could increase the number of potential candidate vaccines available, which may enable selection of a better candidate. Our study concluded that revising the timeline for vaccine selection could result in substantial epidemiological benefits, particularly at times when additional data help improve the vaccine effectiveness through better antigenic match between vaccine and circulating viruses. However, the uncertainty in timing of antigenic variant emergence and the risk of delaying vaccine decision, along with the harm of transitioning away from egg-based vaccines, should be carefully examined.