Vaccines help your immune system recognize and fight off dangerous germs before they cause illness. By introducing antigens—small pieces of a pathogen—a vaccine trains your immune system to respond quickly if exposed later. When enough people in a community are immune, either from vaccination or previous infection, herd immunity develops. This community protection interrupts the spread of disease, safeguarding even those who can’t be vaccinated or who may not respond well, such as some older adults or people with weakened immune systems.
What diseases require vaccines today? The global vaccine-preventable disease map
To understand which diseases require vaccines today, it’s important to look at global immunization priorities and see where gaps still exist. The landscape of vaccine-preventable diseases has shifted over time. Vaccination policies now focus on infections that cause high illness or death, spread easily, or have severe outcomes. The World Health Organization (WHO) sets global policy for COVID-19, influenza, and pneumococcal vaccines. Countries adapt this guidance to meet their local needs.
Respiratory illnesses remain a top concern. COVID-19, caused by SARS-CoV-2, still calls for ongoing vaccination. Vaccines help reduce surges, protect those at highest risk, and prevent hospital overcrowding. Influenza, a seasonal virus that causes fever, cough, and body aches, requires yearly vaccination since the strains change. Respiratory Syncytial Virus (RSV) is especially dangerous for infants and older adults. New RSV vaccines for older adults and pregnant people help protect newborns. A long-acting antibody also offers passive protection for infants.
Routine childhood vaccination programs form the backbone of global immunization. The original six diseases targeted by the WHO Expanded Programme on Immunization were measles, polio, diphtheria, pertussis (whooping cough), tetanus, and tuberculosis. These were chosen because they caused high child mortality and could be prevented by vaccines. Many countries have since added vaccines for Haemophilus influenzae type b, pneumococcal disease, rotavirus, and hepatitis B. These additions have further reduced deaths from pneumonia, meningitis, and diarrhea. By the end of 2024, rotavirus vaccine was used in 131 countries, achieving a global coverage of 59% (Source: who.int, 2025). Polio eradication remains a major goal. In 2024, 84% of infants received three doses of polio vaccine, and polio now remains endemic only in Afghanistan and Pakistan (Source: who.int, 2025).
Travel changes disease risk. Vaccines for travelers protect against diseases found in certain regions and may be required for entry. Depending on your destination and activities, vaccines can prevent:
- Yellow fever (required for entry in some countries)
- Japanese encephalitis in rural Asia
- Typhoid fever from contaminated food or water
- Cholera during outbreaks
- Hepatitis A and hepatitis B from contaminated food or blood/body fluids
- Rabies for remote travel or animal contact
- Meningococcal disease for Hajj or travel in the African meningitis belt
- Measles via MMR catch-up for non-immune travelers
- Tetanus/diphtheria/pertussis boosters
- Seasonal influenza
- COVID-19
- Tick-borne encephalitis in parts of Europe
Some countries also recommend a polio booster if there is documented virus circulation. It’s wise for travelers to check vaccine requirements well ahead of time.
However, not all diseases have licensed vaccines yet. For now, there are no approved preventive vaccines for:
- HIV/AIDS
- Hepatitis C virus
- Syphilis
- Gonorrhea
- Chlamydia
- Cytomegalovirus (CMV)
- Epstein–Barr virus (EBV)
- Herpes simplex virus (HSV-1/2)
- Norovirus
- Rhinovirus “common cold”
- West Nile virus
- Zika virus
- Lassa fever
- Nipah virus
- Marburg virus
- Chagas disease
- Leishmaniasis
- Group A Streptococcus
For tuberculosis, the Bacille Calmette–Guérin (BCG) vaccine, developed over a century ago, is still widely used. It mainly protects infants from severe TB but doesn’t prevent the most common form in adults. For Lyme disease, no human vaccine is currently available. While research continues for many of these pathogens, prevention relies on screening, vector control, protective barriers, post-exposure treatments, and timely care until vaccines become available.
To put vaccine needs in context, here are 20 common diseases and conditions seen worldwide. Their frequency and importance vary by region, and vaccines exist for only some:
- Hypertension (no vaccine)
- Ischemic heart disease (no vaccine)
- Stroke (no vaccine)
- Type 2 diabetes (no vaccine)
- Chronic obstructive pulmonary disease (no vaccine)
- Asthma (no vaccine)
- Lower back pain (condition; no vaccine)
- Depression (no vaccine)
- Dental caries (no vaccine)
- Osteoarthritis (no vaccine)
- Upper respiratory infections, including influenza (influenza vaccine available)
- COVID-19 (COVID-19 vaccines available)
- Lower respiratory infections, including pneumococcal pneumonia and RSV disease (pneumococcal vaccines, RSV vaccines for specific groups available)
- Diarrheal diseases, including rotavirus (rotavirus vaccines available)
- Hepatitis B (vaccine available)
- Human papillomavirus-related disease (HPV vaccines available)
- Tuberculosis (BCG for severe pediatric forms; improved adult-preventive vaccines still in development)
- HIV/AIDS (no vaccine)
- Malaria (pediatric vaccines RTS, S/AS01 and R21/Matrix-M available; travel use is limited)
- Measles (MMR vaccine available)
WHO’s Strategic Advisory Group of Experts (SAGE) issues global policy on COVID-19 vaccines, seasonal influenza vaccination, and pneumococcal conjugate vaccines, which countries adapt to their epidemiology and health system capacity.
The Expanded Programme on Immunization initially targeted six diseases—tuberculosis, diphtheria, tetanus, pertussis, poliomyelitis, and measles—because safe, effective vaccines existed and the diseases caused high child mortality.
For international travel, vaccination requirements and recommendations commonly include yellow fever, meningococcal ACWY (e.g., Hajj), polio boosters, and risk-based vaccines such as typhoid, hepatitis A/B, rabies, and Japanese encephalitis.
How do vaccines work and which types exist? From live attenuated to mRNA
Understanding how vaccines work starts with the immune system. Vaccines prepare your body to fight infection by triggering the adaptive immune response. After you receive a vaccine, B cells make antibodies—proteins that attach to germs and help destroy them. T cells also build up memory. This means your body can react faster and more effectively if you encounter the real pathogen. When enough people are vaccinated, herd immunity develops, lowering transmission and protecting the broader community.
History shows the power of vaccines. Through global coordination and vaccination, smallpox was wiped out in 1980. After that, routine smallpox vaccination stopped. This remains the classic example of disease eradication through immunization.
Some vaccines also prevent cancer by stopping infections that can cause it. For instance, human papillomavirus (HPV) is responsible for nearly all cervical cancers and many other types. HPV vaccination reduces precancerous changes. In real-world studies, fewer cases of cervical cancer have occurred in areas with high vaccine uptake.
Different types of vaccines use different methods to teach the immune system:
Live attenuated vaccines contain weakened forms of the germ. They grow enough to trigger a strong immune response but do not cause illness in healthy people. These vaccines usually give long-lasting protection after just one or two doses. Examples include MMR, oral polio, varicella, and yellow fever vaccines. However, they are not recommended during pregnancy or for those with certain immune problems, and they need careful storage.
Inactivated vaccines use germs that are killed or pieces that cannot reproduce. They are safe for people with weakened immunity and during pregnancy, but often require several doses and periodic boosters. Examples are inactivated influenza, inactivated polio, hepatitis A, and rabies vaccines. The DTP vaccine is a classic case, using:
- Toxoids for diphtheria and tetanus (inactivated toxins that prompt the body to make neutralizing antibodies)
- Inactivated or acellular pertussis antigens
Other vaccine technologies include:
- Conjugate vaccines (like pneumococcal or Hib), which link sugars to proteins to help infants develop strong immunity
- Recombinant protein vaccines (such as hepatitis B and HPV), which use only key proteins from the germ
- Viral vector vaccines, which use harmless viruses to deliver genetic instructions
- mRNA vaccines, where your cells make the antigen themselves—this was used for several COVID-19 vaccines
Each vaccine type balances factors like how well it works, safety, how quickly it can be produced, and storage needs.
Global smallpox eradication in 1980 followed sustained surveillance and vaccination, demonstrating that immunization can eliminate a human disease.
In England, introduction of the bivalent HPV vaccine was associated with lower cervical cancer incidence in vaccinated cohorts, with larger reductions in those vaccinated at younger ages.
Live attenuated vaccines replicate and induce strong, long-lasting immunity but are contraindicated in pregnancy and severe immunodeficiency; inactivated vaccines cannot replicate, are safe in these groups, and generally require boosters.
WHO issues policy recommendations on priority vaccines, including COVID-19, seasonal influenza, and pneumococcal conjugate vaccines, to inform national schedules and risk-group strategies.
What vaccines do you need and when? Schedules, school requirements, and travel vaccines
Vaccine recommendations depend on your age, health, job, and where you live. National and local schedules are your best guide. In the UK, the NHS vaccination schedule outlines which vaccines are recommended throughout life, with updates for seasonal risks—such as COVID-19 boosters for certain groups and annual flu shots for children and those at higher risk—alongside the regular childhood and teen vaccines.
School vaccination rules vary. In the United States, children need certain vaccines to attend school. Each state sets its own list, but most require proof of protection against diphtheria, tetanus, pertussis (DTaP/Tdap), polio (IPV), measles, mumps, rubella (MMR), varicella, and hepatitis B. Booster shots for teens and meningococcal ACWY (MenACWY) for older students are also common. Some states require HPV or a second MenACWY for older teens. Medical exemptions are always allowed. Non-medical (religious or personal) exemptions depend on the state.
In the UK, vaccines are not legally required for school, but schools and doctors encourage catch-up doses based on the NHS schedule. Universities often recommend MenACWY and MMR for new students. In Europe, some countries (like France and Italy) require several childhood vaccines for school or daycare. Germany mandates measles immunization for school and childcare, while Australia links early childhood benefits and childcare enrollment to vaccination. In Canada, some provinces require proof of immunization or formal exemption for school. If your family is moving, check the local rules early.
For university students, close living and socializing raise infection risks. Before starting, check you have:
- MMR (measles, mumps, rubella): two doses, since measles outbreaks can happen where immunity is low.
- MenACWY: protects against serious meningococcal disease, which can spread in shared housing.
- HPV: prevents cancers linked to the virus; catch-up is available into early adulthood.
- Tdap booster: to keep up protection, especially if you’ll be in healthcare settings or traveling abroad.
For adults, recommendations change with age and risk. COVID-19 vaccines are now offered seasonally or periodically to older adults, those with chronic health issues, and frontline workers. These are usually timed for respiratory virus season. Annual flu shots are widely recommended, especially during pregnancy, older age, chronic illness, or for healthcare workers. Pneumococcal vaccines are advised for adults 65 and older, or younger adults with certain health risks, using conjugate vaccines (PCV) with or without additional boosters. RSV vaccines are now available in some places for adults 60 and up, and for pregnant people at certain stages to protect newborns.
To keep up with your vaccines, use official schedules and sign up for reminders. In the UK, the NHS schedule is online and in the NHS App; clinics and schools send reminders and offer catch-up clinics. In the US, immunization information systems help track doses and send alerts, with national recommendations updated each year.
Wherever you live, keep an updated vaccination record, opt into reminder messages, check for seasonal updates on COVID-19 and flu every autumn/winter, and review changes at key ages (adolescence, pregnancy, 50, 60, 65). Before international travel, visit a travel clinic 6–8 weeks ahead. If you miss a dose, most schedules allow catch-up without restarting the series—ask your healthcare provider how to get back on track.
How do vaccination rates shape outbreaks? Herd immunity, thresholds, and real-world effectiveness
Vaccination rates play a central role in the risk of disease outbreaks. Outbreaks depend on how many people are immune and how easily a disease spreads. Herd immunity happens when enough people are protected, dropping the reproduction number below 1 and stopping transmission. The coverage needed depends on how contagious the disease is. For measles, which spreads very easily, about 95% two-dose coverage is usually needed to prevent outbreaks. Other diseases like polio or rubella can be controlled with lower coverage. Even the best vaccines can’t prevent outbreaks if coverage falls short in specific areas or groups.
Global vaccine gaps in 2025 are clear from coverage data. DTP3 (the third dose of diphtheria–tetanus–pertussis vaccine) is a key measure of program strength. In 2024, DTP3 coverage was 85%, and 14.3 million children received no doses at all (Source: who.int, 2025). Measles coverage shows a similar pattern. In 2024, first-dose coverage was 84%, second-dose was 76%, and 20.6 million children missed their first dose (Source: who.int, 2025). When first doses stall and second doses lag, immunity gaps grow, leading to measles outbreaks, even in countries with high national averages.
These trends are especially important in the WHO African Region, where measles outbreaks have surged as immunity gaps widened during health service disruptions. UNICEF helps by supporting vaccine supply, cold-chain systems, and community outreach, as well as responding to outbreaks with the Measles & Rubella Partnership. Together with health ministries, these groups run catch-up campaigns and strengthen routine vaccination. The Immunization Agenda 2030 (IA2030) is the global strategy to reduce the number of children who get no vaccines, expand vaccination across the lifespan, and make immunization programs more resilient.
Polio provides another example. The wild virus still circulates in Afghanistan and Pakistan, where conflict and limited access make vaccination difficult. High polio vaccination rates elsewhere prevent the virus from returning. For measles, outbreaks cluster where two-dose MMR uptake falls below the needed threshold. Quick response campaigns and school-based catch-up can stop outbreaks if done quickly.
High vaccine coverage lowers hospitalizations and deaths from respiratory viruses during peak seasons. Conjugate vaccines for pneumococcus also protect unvaccinated people by reducing the spread among children. Both individual and community protection depend on keeping coverage high. In practice, making sure every child gets routine vaccines, finishing two-dose measles series, and staying up to date with boosters are key to lowering outbreak risk.
How are new vaccines for emerging diseases developed and tested?
When a new disease appears or an old one resurges, scientists and public health groups follow a careful process called the vaccine development pipeline. This starts with discovering which parts of the germ can trigger a protective response. Next, the process moves through lab and animal testing, followed by clinical trials in people, and finally to approval and ongoing safety checks.
During health emergencies, the WHO brings together scientists, regulators, and funders to speed up research. The WHO R&D Blueprint sets priorities, defines what a successful vaccine should look like, and standardizes how trials are run. This coordination helps studies answer important questions quickly and lets results be compared across countries.
Discovery and preclinical work begin with designing the right antigen and choosing the best technology. Candidate vaccines are tested in the lab and in animals for safety and how well they trigger immunity. If results are promising, the vaccine moves to human trials under strict safety rules.
Phase I trials test safety and immune response in small groups of healthy adults. Phase II trials expand to hundreds of people to refine dosing and check safety. Phase III trials include thousands or more, testing if the vaccine really prevents disease. For fast-moving outbreaks or rare diseases, trial designs may use ring vaccination, cluster randomization, or other special approaches. Sometimes, if placebo trials aren’t possible, researchers compare immune responses to those seen with proven vaccines. Regulators and independent boards review all data.
In emergencies, authorities may use conditional or emergency approvals. WHO’s Emergency Use Listing helps countries buy and use new vaccines quickly. Manufacturing is scaled up under strict quality controls, and logistics are planned for storage, transport, and tracking. Once a vaccine is used, safety and effectiveness are monitored in real time. Manufacturing can be adjusted if the germ changes. Ongoing studies track how well the vaccine works in the real world, how long protection lasts, and if rare side effects appear. These data guide future booster or next-generation vaccine policies.
Are vaccines safe? Side effects, contraindications, and monitoring systems
Vaccine safety is built on careful trials and ongoing monitoring. Every approved vaccine has a known safety profile, and regulators require both pre-approval and post-approval studies to spot common and rare side effects. The flu vaccine is a good example. Inactivated flu shots most often cause mild, short-lived reactions like arm soreness, redness, or swelling. Sometimes, people experience fatigue, mild fever, headache, or muscle aches within 1–2 days. The live nasal flu vaccine may cause a stuffy nose or mild wheezing in young children. Serious allergic reactions are rare. If someone has had Guillain–Barré syndrome within six weeks of a previous flu shot, doctors weigh the risks and benefits carefully, since the flu itself can also cause nerve problems. People with a severe allergy to a vaccine ingredient or a previous dose should not get that vaccine. Live nasal flu vaccine is usually avoided during pregnancy or for people with weak immune systems.
Not every injection for prevention is a vaccine. The RSV antibody is a monoclonal antibody that gives passive protection against RSV; it doesn’t make your immune system create its own antibodies. For infants and some high-risk groups, one long-acting dose before or during RSV season can lower the risk of hospitalization. Side effects are usually mild, like redness at the injection site or a rash; serious allergy is rare but needs urgent care if it happens. Since this is passive immunization, it doesn’t cause the typical vaccine reactions and can often be given with regular childhood vaccines.
Some vaccines have unique side effects because of how they’re made or given. The BCG vaccine for tuberculosis, given under the skin, often causes a small nodule that may ulcerate and then heal over weeks. The nearby lymph node may swell. Rarely, more serious problems like lymph node infection or bone infection can occur, and infants with severe immune problems can develop widespread BCG disease. For this reason, BCG is not given during pregnancy or to people with known immune deficiency. Proper injection technique, correct dosing, and good storage practices help minimize local reactions.
Three main safeguards support vaccine safety. First, national guidelines include clear rules on who should and shouldn’t get each vaccine, with alternatives when needed. Second, passive reporting systems and manufacturer monitoring collect reports of possible side effects, which are then checked for patterns and background rates. Third, active monitoring and large databases help detect rare problems and compare risks after vaccination with risks from the disease itself. For most people, vaccine side effects are mild and brief, and the benefits—lower risk of disease, hospitalization, and lasting complications—far outweigh the risks.
Avoiding pitfalls: timing, documentation, and tips to maximize protection
To get the most from vaccines, timing, good records, and follow-up matter. Protection depends not just on which vaccines you get, but when you get them and how well you track them. Timely doses, completing the series, and having proof of vaccination all help ensure you’re protected when you need it—whether as a baby, a student, or a traveler.
The first vaccine dose primes your immune system and starts building memory. For some diseases, this gives partial protection within about two weeks, but it’s often not enough. Most schedules require two doses to finish the primary series and lock in strong, lasting immunity. Examples include:
- Two-dose MMR for measles
- Two-dose HPV for teens
- Two-dose varicella
If you skip or delay the second dose, you may remain vulnerable, especially during outbreaks or travel.
Timing is especially critical at birth for infections passed from mother to child. A birth dose of hepatitis B, given soon after delivery, reduces the risk of early infection and chronic disease. In 2024, global coverage for the full hepatitis B series was 84%, but timely birth-dose coverage was only 45% (Source: who.int, 2025). Improving postnatal routines, stocking vaccines in maternity wards, and offering after-hours coverage can help close this gap and provide earlier protection.
Good documentation is essential. Keep a single, up-to-date vaccination record with the product name, lot number, date, and injection site. Take photos or scan paper cards, store digital copies in a secure cloud folder or health app, and ask your clinic to update your national or state immunization system. When moving or switching doctors, bring both printed and digital records so your new provider can place you on the right catch-up schedule. For travel, some countries require official certificates for certain vaccines, so allow time to get the right paperwork.
For large gatherings like Umrah, careful timing is key. This pilgrimage to Mecca draws people year-round and raises infectious risk. Plan vaccines at least a month ahead. Proof of a recent meningococcal ACWY dose may be required, and some travelers need a polio booster or documentation if coming from certain areas. It’s common to update routine vaccines and get flu and COVID-19 shots before travel. Rules may change each year, so check requirements with the Saudi Ministry of Health, your embassy, or a travel clinic, and make sure doses are given early enough to count.
If you fall behind, you usually don’t need to start over. Most schedules have minimum intervals between doses, so your provider can build a catch-up plan that makes use of doses you’ve already received. You can often get several vaccines at once to finish multiple series in a single visit. After finishing, set reminders for boosters that maintain protection, like tetanus or periodic respiratory virus updates based on your age and risk.
Speeding up HPV coverage to 2030 targets means reaching 90% first-dose among girls, then making sure the series is completed where two doses are needed. Helpful tactics include:
- School-based vaccination with opt-out consent
- Multi-age group campaigns at program start
- Reminders by text or school portal
- Vaccination in various settings with flexible hours
- Single-dose schedules where allowed
- Training providers to give strong recommendations
- Removing barriers, such as fees, and bringing vaccines to communities
Tracking first-dose and series completion separately helps teams find and support those who need to finish the series.
Finally, match your vaccine schedule to your risk. Before travel, moving into shared housing, or the start of respiratory virus season, check that you’re on track for both the first and follow-up doses, and allow at least two weeks after the last dose for full protection. Well-timed vaccination, careful documentation, and proactive follow-up together offer the strongest protection when it matters most.