Coronavirus Vaccines

Historical Development

Traditional vaccine development timelines span 10–15 years. COVID-19 vaccines were developed and authorized within 11 months of the virus's genetic sequence being published — a feat explained by several factors:

• Pre-existing research platform: mRNA vaccine technology had been in development for over a decade at Moderna and BioNTech, with earlier work targeting MERS-CoV providing a blueprint for spike protein targeting.
• Massive parallel investment: Operation Warp Speed (U.S.) and similar programs globally committed funding for manufacturing at-risk before trial completion, compressing timelines.
• Overlapping trial phases: Phases 1, 2, and 3 were conducted with significant overlap rather than sequentially.
• Emergency regulatory pathways: FDA Emergency Use Authorization (EUA) and WHO Emergency Use Listing (EUL) enabled rapid deployment while full approval processes continued.
• High enrollment rates: Over 40,000 participants in the Pfizer Phase 3 trial alone yielded statistically robust results quickly.^[V1]

The 2026–2027 season: current formulation and who is advised to get it

COVID-19 vaccines are reformulated each year to track the evolving virus, much as seasonal flu shots are. For the 2026–2027 season beginning in fall 2026, the U.S. Food and Drug Administration advised manufacturers that the updated shot should be a monovalent JN.1-lineage XFG formulation. FDA's Vaccines and Related Biological Products Advisory Committee (VRBPAC) made this recommendation at its May 28, 2026 meeting, after reviewing which SARS-CoV-2 variants were circulating and how well existing vaccines matched them.^[V4]

The World Health Organization's advisory group (TAG-CO-VAC) reached a closely related conclusion in its May 16, 2026 statement, recommending a monovalent LP.8.1 antigen while noting that other JN.1-lineage options — including JN.1, KP.2, XFG and NB.1.8.1 — remain acceptable where they produce broad neutralizing responses. Both bodies are targeting descendants of the JN.1 Omicron lineage that has driven most transmission worldwide since 2024.^[V5]

Who is advised to get it: U.S. eligibility narrowed during 2025. The FDA now frames approval of the updated COVID-19 vaccines around adults aged 65 and older and younger people who have an underlying condition that raises their risk of severe COVID-19 — and the youngest approved age differs by product, from 6 months (Spikevax) to 12 years (mNEXSPIKE, Nuvaxovid), as the table below shows. In September 2025 the CDC's Advisory Committee on Immunization Practices (ACIP) shifted to individual-based (shared clinical) decision-making — advising that people decide about vaccination together with a health-care provider rather than under a blanket universal recommendation. This guidance has changed more than once, so confirm the current CDC recommendation and weigh your own risk factors before the season.^[V6]

Novavax vs Pfizer vs Moderna for 2026–2027: who each one is approved for

All four COVID-19 vaccines licensed in the U.S. received FDA approval for their 2026–2027 Formula on August 27, 2026. They are not interchangeable on eligibility: each product's FDA indication sets a different youngest age for people under 65 with a high-risk condition. This is the practical difference most people asking "Novavax or Pfizer?" run into first, and it is set by the label, not by efficacy.^[V9]

*Every product is approved for everyone 65 and older. Under 65, each is approved only for people with at least one underlying condition that puts them at high risk of severe COVID-19, starting from the age shown.

Read the table with two cautions. The dose figures are not comparable across rows: micrograms of mRNA and micrograms of protein measure different things, and a lower number does not mean a weaker vaccine. And an FDA indication is not the same as a CDC recommendation, which is made separately (see above) and has changed more than once since 2025.

Each of the three original COVID-19 vaccines available in the United States has a pivotal phase 3 trial behind it, published in the New England Journal of Medicine. Below is what each one enrolled, what it found, and — the part almost always omitted — the confidence interval around the headline figure.

Why those three numbers cannot be ranked

They faced different viruses. As published in the NEJM, the two mRNA trials accrued their cases in the second half of 2020, before any named variant of concern was circulating widely — effectively against the ancestral strain. PREVENT-19 ran from late December 2020 into 2021, and the Novavax investigators sequenced the breakthrough cases: 48 of 61 (79%) were variants of concern or interest, and 31 of the 35 variant-of-concern genomes (89%) were Alpha. Against those variants specifically, Novavax efficacy was 92.6% (83.6–96.7). A vaccine tested against a harder target and scoring 90.4% has not been shown to be worse than one tested against an easier target and scoring 95%.

The intervals overlap. In the NEJM reports, Pfizer's interval runs from 90.3% to 97.6% and Novavax's from 82.9% to 94.6%. Those ranges share the band from 90.3% to 94.6%. A difference you cannot separate from sampling noise is not a difference you can act on.

The endpoints differ. Pfizer counted cases from 7 days after the second dose; Moderna from 14 days. Both counted symptomatic, laboratory-confirmed COVID-19, but the case definitions and the surveillance intensity were set by each sponsor's protocol, not by a common standard.

None of them measured the current formulations. Every one of those trials tested a vaccine encoding the 2019 ancestral spike protein, in a population with essentially no prior immunity. Today's shots encode a JN.1-lineage spike and are given to a population in which the great majority have been infected, vaccinated, or both. Annual reformulations are authorised on immunogenicity — the antibody response they produce — not by repeating a 30,000-person efficacy trial each year, the same regulatory pathway used for influenza vaccines.

There has never been a head-to-head trial. No randomised trial has assigned participants to Pfizer versus Moderna versus Novavax and compared outcomes directly. Observational comparisons exist, but they compare people who chose different products at different times, which is not the same thing. The honest answer to "which is best" is that the trial evidence does not support a ranking; the evidence supports the statement that all three substantially reduced symptomatic COVID-19 in their trial populations.

What does differ between them

• Platform. Pfizer and Moderna deliver mRNA in a lipid nanoparticle; the cell makes the spike protein. Novavax delivers the spike protein itself, manufactured in insect cells and assembled into nanoparticles, with the saponin-based Matrix-M adjuvant. This is the practical distinction for someone who prefers a protein-subunit vaccine, a platform used in hepatitis B and pertussis vaccines for decades.
• Dose. Moderna's primary series used 100 µg of mRNA, Pfizer's 30 µg — a real difference in antigen quantity, though the trials were not designed to compare them.
• Reactogenicity. All three trials reported more injection-site and systemic reactions in the vaccine arms than in placebo, mostly mild to moderate and transient, and more frequent after the second dose. PREVENT-19 reported this pattern explicitly; the mRNA trials described comparable profiles.
• Serious adverse events. In all three pivotal trials the incidence of serious adverse events was low and similar between vaccine and placebo groups. Myocarditis and pericarditis after mRNA vaccination — concentrated in adolescent and young-adult males — were identified later, through post-authorisation surveillance, not in these trials, which were not large enough to detect events at that rate.

What is not known

• Current-season effectiveness against infection. Because the annual reformulation is authorised on immunogenicity, there is no efficacy trial of the 2026–2027 formula. Effectiveness estimates arrive later, from observational networks, and carry the confounding those designs always have.
• The durability question for a hybrid-immunity population. The pivotal trials measured a median of about two months of follow-up in immunologically naive people. How long the current shots add protection on top of repeated prior infection is an active research question, not a settled number.
• Whether platform choice changes outcomes for an individual. No trial has been designed to answer it.

For how those vaccine-related risks compare with the disease they reduce, see our COVID-19 Risk Perspective and the hub's Virus Risk Perspective, which sets COVID-19 beside 14 other viruses on the same measures. Claims that circulate about the vaccines themselves — microchips, infertility, DNA alteration — are addressed with the trial and surveillance evidence on our anti-vaccine claims page.

This is informational context, not medical advice. Whether to be vaccinated, and with which product, is a decision to make with a healthcare provider who knows your history.