The two malaria vaccines given to young children in Africa, RTS,S and R21, work best in the first year after the main doses and then gradually lose strength. That is why they come as a schedule of four doses, with the later dose there to top protection back up before malaria season returns.1World Health Organization. Malaria vaccines (RTS,S and R21) How long protection holds depends less on the calendar than on how much malaria is around a child and which vaccine they got.
How Much Protection Is Left Each Year
After three doses of RTS,S, children had about 36% to 44% fewer malaria illnesses than unvaccinated children in the first year.2PubMed Central. Seven-Year Efficacy of RTS,S/AS01 Malaria Vaccine among Young African Children3PubMed Central. Four-Year Efficacy of RTS,S/AS01E and Its Interaction with Malaria Exposure By the fourth year that advantage had fallen to about zero.4PubMed Central. Four-Year Efficacy of RTS,S/AS01E and Its Interaction with Malaria Exposure In a seven-year follow-up it was still only about 4% in year seven.5PubMed Central. Seven-Year Efficacy of RTS,S/AS01 Malaria Vaccine among Young African Children
A 40% reduction means fewer bouts of malaria, not that a child can’t get it. A vaccinated child can still get sick, so a fever still needs a test. Protection is strongest in the early months after the doses and weaker later in the year, so a fever late in the year doesn’t mean the vaccine didn’t work.
The fade happens in two steps, fast then slow. Most of the protective antibodies made after vaccination fade within the first three to six months.6PubMed Central. A combined analysis of immunogenicity, antibody kinetics and vaccine efficacy from phase 2 trials of the RTS,S malaria vaccine7PubMed Central. Seven-year kinetics of RTS, S/AS01-induced anti-CSP antibodies in young Kenyan children A smaller, longer-lasting share declines slowly over the next four years.8PubMed Central. Immunogenicity of the RTS,S/AS01 malaria vaccine and implications for duration of vaccine efficacy: secondary analysis of data from a phase 3 randomised controlled trial9PubMed Central. A combined analysis of immunogenicity, antibody kinetics and vaccine efficacy from phase 2 trials of the RTS,S malaria vaccine
Antibody levels in vaccinated children still stayed above those of unvaccinated children for seven years.10PubMed Central. Seven-year kinetics of RTS, S/AS01-induced anti-CSP antibodies in young Kenyan children Even so, protection against infection in babies 5 to 17 months old is estimated to start near 74%, fall to about 28% at one year, and reach about 9% after five years.11PubMed Central. Immunogenicity of the RTS,S/AS01 malaria vaccine and implications for duration of vaccine efficacy: secondary analysis of data from a phase 3 randomised controlled trial In babies vaccinated at 6 to 12 weeks, it falls faster, to about 11% at one year, which is part of why WHO starts the vaccine around 5 months.12PubMed Central. Immunogenicity of the RTS,S/AS01 malaria vaccine and implications for duration of vaccine efficacy: secondary analysis of data from a phase 3 randomised controlled trial13World Health Organization. Malaria vaccines (RTS,S and R21)
How Booster Doses Restore Protection
WHO recommends four doses starting around 5 months of age.14World Health Organization. Malaria vaccines (RTS,S and R21) The reason is that a fourth dose 18 months after the first series restores the protection that had faded.15PubMed Central. Antibody responses to the RTS,S/AS01E vaccine and Plasmodium falciparum antigens after a booster dose within the phase 3 trial in Mozambique For RTS,S, a booster at 18 months raises estimated protection against infection back to about 59%, leaving about 17% at five years versus 9% without.16PubMed Central. Immunogenicity of the RTS,S/AS01 malaria vaccine and implications for duration of vaccine efficacy: secondary analysis of data from a phase 3 randomised controlled trial After an R21 booster, antibody levels return within a month to about where they were after the first doses.17University of Oxford. Malaria booster vaccine continues to meet WHO-specified 75% efficacy goal Because the body already remembers the vaccine from the first series, a booster can lift antibodies quickly.
Repeated boosters help, but each gives a smaller lift. When RTS,S boosters were given every year before malaria season, each one raised antibodies less than the one before.18PubMed Central. The anti-circumsporozoite antibody response to repeated, seasonal booster doses of the malaria vaccine RTS,S/AS01E Still, WHO says a fifth dose a year after the fourth may be considered where malaria stays a high risk into age three or beyond, or comes in a sharp season.19World Health Organization. Malaria vaccines (RTS,S and R21) That is a country-level decision, so some programmes offer it and others do not.
If the fourth dose was missed, a late dose still boosts protection; the series does not need to restart. Ask the clinic to check the vaccination card and give the missing dose, and ask whether a fifth dose is offered in your area.
Does R21 Last Longer Than RTS,S
In seasonal-malaria areas, R21 cut symptomatic malaria by 75% in the year after three doses.20World Health Organization. WHO recommends R21/Matrix-M vaccine for malaria prevention in updated advice on immunization Across other settings it cut cases by 66% in that first year.21World Health Organization. WHO recommends R21/Matrix-M vaccine for malaria prevention in updated advice on immunization After a booster one year later, children had about 80% fewer malaria illnesses through the next year.22PubMed. Efficacy and immunogenicity of R21/Matrix-M vaccine against clinical malaria after 2 years’ follow-up in children in Burkina Faso: a phase 1/2b randomised controlled trial About 4 in 10 boosted R21 children got malaria that year, versus nearly 9 in 10 unvaccinated children.23PubMed. Efficacy and immunogenicity of R21/Matrix-M vaccine against clinical malaria after 2 years’ follow-up in children in Burkina Faso: a phase 1/2b randomised controlled trial Even with a booster, a large share of R21 children still caught malaria, so the vaccine lowers risk rather than removing it.
Both vaccines train the body to attack the parasite just after a mosquito bite, before it reaches the blood.24PubMed Central. Quantitative and Clinical Pharmacology Perspectives on Next‐Generation Malaria Prevention Using Vaccines and Long‐Acting Monoclonal Antibodies WHO gives them the same four-dose schedule, and a country uses whichever it has available.25World Health Organization. Malaria vaccines (RTS,S and R21) Parents usually can’t choose, since it depends on the national programme.
R21’s two-year results come from one area of Burkina Faso with seasonal malaria, so long-term figures elsewhere are still being gathered.26PubMed. Efficacy and immunogenicity of R21/Matrix-M vaccine against clinical malaria after 2 years’ follow-up in children in Burkina Faso: a phase 1/2b randomised controlled trial RTS,S has been followed for up to seven years, so its long fade is known in detail while R21’s is still being measured.
Why Protection Fades Faster in High-Malaria Areas
Protection fell faster over time in children exposed to more malaria.27PubMed Central. Four-Year Efficacy of RTS,S/AS01E and Its Interaction with Malaria Exposure These children also made fewer working antibodies after vaccination.28PubMed Central. Induction, decay, and determinants of functional antibodies following vaccination with the RTS,S malaria vaccine in young children In the lowest-malaria areas, three-dose protection fell from 88% to 15% over four and a half years.29PubMed Central. Malaria Transmission Intensity Likely Modifies RTS, S/AS01 Efficacy Due to a Rebound Effect in Ghana, Malawi, and Gabon In the highest-malaria areas it fell from 82% to below zero over the same time.30PubMed Central. Malaria Transmission Intensity Likely Modifies RTS, S/AS01 Efficacy Due to a Rebound Effect in Ghana, Malawi, and Gabon
Children who get malaria repeatedly slowly build some natural resistance.31PubMed Central. Malaria Transmission Intensity Likely Modifies RTS, S/AS01 Efficacy Due to a Rebound Effect in Ghana, Malawi, and Gabon Because vaccinated children were shielded early, they build that resistance more slowly, so a few more cases can show up at older ages.32PubMed Central. Public health impact and cost-effectiveness of the RTS,S/AS01 malaria vaccine: a systematic comparison of predictions from four mathematical models In year five of one study, vaccinated children in heavy-malaria areas had about 57% more cases than unvaccinated children that year.33PubMed Central. Seven-Year Efficacy of RTS,S/AS01 Malaria Vaccine among Young African Children Counted over 15 years, though, the vaccine still prevents far more illness and death than it shifts to later.34PubMed Central. Public health impact and cost-effectiveness of the RTS,S/AS01 malaria vaccine: a systematic comparison of predictions from four mathematical models
Parasite strain also matters. RTS,S protected better against strains that closely match the vaccine, about 50% versus 33% for others in the first year.35PubMed Central. Impacts of Ecology, Parasite Antigenic Variation, and Human Genetics on RTS,S/AS01e Malaria Vaccine Efficacy In Ethiopia, none of the strains tested matched the vaccine’s version, so it may protect less there.36Scientific Reports. Unveiling mismatch of RTS S AS01 and R21 Matrix M malaria vaccines haplotype among Ethiopian Plasmodium falciparum clinical isolates Severe malnutrition and lack of vitamin A or D can also weaken how many antibodies a child makes.37World Journal of Advanced Research and Reviews. Investigation of the Immune Response to Malaria Vaccines
Why Timing Before Malaria Season Matters
Where malaria mostly strikes in a 4- to 5-month rainy season, WHO lets countries give doses just before it.38World Health Organization. Malaria vaccines (RTS,S and R21)39World Health Organization. WHO recommends R21/Matrix-M vaccine for malaria prevention in updated advice on immunization Protection is strongest in the first months after a dose, so peak protection covers the riskiest months. Timing doses this way prevented more cases than giving them by age alone, an estimated 14,000 to 47,000 extra per 100,000 young children over 15 years.40PubMed. Seasonal use case for the RTS,S/AS01 malaria vaccine: a mathematical modelling study
In a seasonal area, clinics may call children in during the months before the rains, and the yearly booster may come at the same time each year. Mark the season start on a calendar and check the card before it.
In many seasonal areas, children also get monthly antimalarial medicine during the rainy season, often called seasonal malaria chemoprevention (SMC). Children given both had about 113 malaria episodes per 1,000 per year, versus about 278 with the vaccine alone and 305 with medicine alone.41PubMed. Seasonal Malaria Vaccination with or without Seasonal Malaria Chemoprevention
The medicine only protects during the weeks it is taken, while vaccine protection fades more gradually. If your area runs a seasonal medicine campaign, keep giving it to a vaccinated child.
Who Can Get the Malaria Vaccine
WHO recommends the vaccine for children from about 5 months of age, mainly in areas of moderate and high malaria.42World Health Organization. Malaria vaccines (RTS,S and R21) Countries may also offer it in lower-malaria areas based on cost and their overall plan.43World Health Organization. Malaria vaccines (RTS,S and R21) It is not licensed or recommended as a travel vaccine, so travellers rely on antimalarial pills and bite prevention. Adults living in malaria areas aren’t routinely vaccinated.
Travellers should take the prescribed antimalarial for the full course, including after returning. Sleeping under a treated net and using repellent add protection. Any fever within months of returning needs a malaria test, and the doctor should hear about the trip.
Keeping a Child Protected as the Vaccine Fades
WHO says malaria vaccines should be part of a wider malaria-control plan.44World Health Organization. Malaria vaccines (RTS,S and R21) Vaccination alone lowers illness but isn’t enough to end malaria.45Discover Public Health. Modeling the public health impact of partial vaccination and vector control strategies on malaria transmission So vaccinated children should still sleep under an insecticide-treated net every night, and any fever in a child in a malaria area should be tested the same day. Models estimate about 484 deaths prevented per 100,000 vaccinated children.46PubMed Central. Public health impact and cost-effectiveness of the RTS,S/AS01 malaria vaccine: a systematic comparison of predictions from four mathematical models
Longer-lasting options are being developed. Researchers are testing mRNA malaria vaccines, the same type used for COVID-19.47PubMed Central. Current Developments in Malaria Vaccination: A Concise Review on Implementation, Challenges, and Future Directions In one early study an mRNA vaccine’s antibodies lasted about 2.5 times longer than a standard protein vaccine’s, though it targets a different malaria type.48PubMed Central. A Pvs25 mRNA vaccine induces complete and durable transmission-blocking immunity to Plasmodium vivax Lab-made antibody injections give immediate protection that lasts as long as the drug stays in the body.49PubMed Central. Quantitative and Clinical Pharmacology Perspectives on Next‐Generation Malaria Prevention Using Vaccines and Long‐Acting Monoclonal Antibodies None of these are available for children yet, so current vaccines and boosters remain the option.