# DHPP Vaccine for Dogs: What It Covers, Schedule, Side Effects The DHPP vaccine is the core combination vaccine that protects dogs against four diseases: canine distemper virus, canine adenovirus (infectious hepatitis), [canine parvovirus](/knowledge/veterinary-medicine/viral-diseases/canine-parvovirus), and canine parainfluenza virus. It is often called the 5 in 1 vaccine for dogs when a leptospirosis component is added, and it appears on veterinary records under several names including DAPP, DA2PP, and DHLPP. Puppies receive a series of doses every 2 to 4 weeks until they are at least 16 weeks old, a booster within one year, and then revaccination no more often than every 3 years. Most dogs experience only mild, short-lived reactions such as soreness at the injection site, low energy, or a reduced appetite for a day. Facial swelling, hives, vomiting, and difficulty breathing are emergencies that require immediate veterinary care. This article is educational and is not a substitute for veterinary diagnosis or treatment. ## The Short Answer for Owners If you want the practical summary before the science, here it is. - **What it covers:** four viral diseases that are either frequently fatal or capable of causing lifelong organ damage. Distemper attacks the nervous system and respiratory tract. Parvovirus causes severe hemorrhagic gastroenteritis. Adenovirus causes liver disease. Parainfluenza contributes to infectious tracheobronchitis (kennel cough). - **When puppies get it:** a series of doses starting as early as 6 to 8 weeks of age, repeated every 2 to 4 weeks, with the final dose given at 16 weeks of age or older. - **When adults get it:** a booster within one year of the puppy series, then every 3 years for immunocompetent dogs. - **How often side effects occur:** mild reactions are common and resolve within 24 to 48 hours. Serious reactions are uncommon. - **What to do if you see a reaction:** mild lethargy, soreness, or a small lump at the injection site can be monitored at home. Swelling of the face, hives, repeated vomiting, or labored breathing require an immediate call to a veterinarian or an emergency clinic. ## At a Glance: DHPP Naming Variants and What Each Letter Means Veterinary clinics use several abbreviations for the same core vaccine. The letters tell you which antigens are included. The table below decodes the common variants you will see on a vaccination certificate. | Abbreviation | Letters decoded | What it protects against | Notes | |--|--|--|--| | DHPP | Distemper, Hepatitis (adenovirus), Parvovirus, Parainfluenza | CDV, CAV-2, CPV-2, CPiV | The most common US abbreviation | | DAPP | Distemper, Adenovirus, Parvovirus, Parainfluenza | Same four antigens | "A" replaces "H" because adenovirus is the modern term | | DA2PP | Distemper, Adenovirus type 2, Parvovirus, Parainfluenza | Same four antigens | The "2" specifies the adenovirus type used in the vaccine | | DHLPP | Distemper, Hepatitis, Leptospirosis, Parvovirus, Parainfluenza | The four core antigens plus Leptospira | Leptospirosis is non-core and given based on risk | | 5 in 1 vaccine for dogs | Colloquial name | Usually the four core antigens plus leptospirosis | The "5" refers to the number of disease components, not the number of injections | The distinction between DAPP and DHPP is historical rather than clinical. The vaccine antigen is canine adenovirus type 2 (CAV-2), which cross-protects against canine adenovirus type 1 (CAV-1), the virus that causes infectious canine hepatitis [1]. Older records use "H" for hepatitis. Modern records use "A" for adenovirus. Both refer to the same protective component. The "5 in 1" label is a marketing and convenience term. It usually means the four core viral antigens plus a leptospirosis fraction. Leptospirosis is a bacterial disease and is classified as non-core by the American Animal Hospital Association (AAHA), meaning it is recommended based on a dog's individual exposure risk rather than for every dog [2][3]. ## Why Each Component Matters ### Distemper (D) Canine distemper virus (CDV) is a morbillivirus related to human measles. It spreads through respiratory droplets and contaminated secretions. Infection can begin as a respiratory and gastrointestinal illness and progress to neurologic disease, including seizures and myoclonus. Distemper is often fatal, and survivors frequently have permanent neurologic deficits. Vaccination against CDV is highly effective. In a challenge study, dogs vaccinated at 7 and 11 weeks of age with a multivalent modified-live vaccine were protected against virulent CDV challenge for a minimum of 3 years following the second vaccination [1]. A separate study confirmed protection against distemper challenge more than 4 years after initial vaccination [4]. ### Hepatitis (H) or Adenovirus (A) Canine adenovirus type 1 causes infectious canine hepatitis, a disease that damages the liver, blood vessels, and sometimes the cornea (a condition historically called blue eye). The vaccine uses CAV-2, a related strain that cross-protects against CAV-1 but causes fewer adverse effects than older CAV-1 vaccines [1]. In the same 3-year challenge study, clinical signs of CAV-1 infection were prevented in 100% of vaccinated dogs [1]. Another study confirmed protection against infectious canine hepatitis challenge 55 to 57 months after initial vaccination [4]. ### Parvovirus (P) Canine parvovirus type 2 (CPV-2) is the most common severe viral cause of acute hemorrhagic gastroenteritis in puppies. It is highly contagious and environmentally persistent. Mortality in untreated puppies can be high, and treatment requires intensive supportive care. Parvovirus has evolved since it emerged in the late 1970s. Variants known as CPV-2a, CPV-2b, and CPV-2c have emerged through mutations in the VP2 capsid protein, and CPV-2c has become the predominant strain in parts of Europe and South America [5]. Modern vaccines are formulated to provide broad cross-protection against these variants. Duration of immunity studies for parvovirus consistently show protection well beyond one year. A study of client-owned dogs found antibody responses against CPV-2 and CAV-1 persisted for at least 36 months after vaccination with a combination product [6]. Another study found that 98.7% of dogs were serological responders to CPV-2 even when last vaccinated 1.5 to 9 years earlier [7]. ### Parainfluenza (P) Canine parainfluenza virus (CPiV) is one of the pathogens involved in infectious tracheobronchitis, commonly called kennel cough. It is rarely fatal on its own but contributes to a harsh, dry cough that can persist for weeks and can predispose dogs to secondary bacterial pneumonia. The parainfluenza component is included in the core combination vaccine because it is a common respiratory pathogen in group settings. ## The DHPP Vaccine Schedule The schedule for the DHPP vaccine is built around two principles: puppies have maternal antibodies that can block vaccine response, and immunity from modified-live core vaccines lasts at least 3 years in most dogs. ### Puppy Series According to the AAHA Canine Vaccination Guidelines, puppies should receive the core combination vaccine starting at 6 to 8 weeks of age, with doses repeated every 2 to 4 weeks until the puppy is at least 16 weeks old [2][3]. The final dose must be given at 16 weeks or later because maternal antibodies can persist until that age and interfere with vaccine take. The number of doses a puppy receives depends on when the series starts. A puppy that starts at 6 weeks may receive four doses. A puppy that starts at 12 weeks may receive two or three. The rule is not a fixed number of injections. The rule is that the last dose must be given at 16 weeks of age or older. The AAHA guidelines also address the immunity gap, the window during which maternal antibodies have waned enough to stop protecting the puppy but are still high enough to block the vaccine [2]. This gap is why the series is repeated rather than given as a single injection. ### Booster Within One Year After the puppy series is complete, the AAHA guidelines recommend a booster dose within one year [2][3]. This booster is not a "repeat" of the puppy series. It is a final step that ensures any puppy whose immune system did not fully respond to the series (because of residual maternal antibody interference or individual variation) receives a second chance at protection. In most dogs, this booster establishes durable immunity that will last for years. ### Adult Revaccination Every 3 Years For immunocompetent adult dogs, the AAHA guidelines recommend revaccination with the core combination vaccine no more often than every 3 years [2][3]. This interval is based on challenge studies and serologic data showing a minimum duration of immunity of 3 years for CDV, CAV-2, and CPV-2 [8][1][9]. Some studies have shown protection lasting 4 years or longer [4], and serologic surveys have found that many dogs remain seropositive for 5 to 9 years after their last vaccination [7][10]. The 3-year interval is not a maximum. It is a minimum recommended revaccination interval. Many dogs remain protected well beyond 3 years, which is why titer testing is an option for owners who want to avoid unnecessary vaccination. ### Adult Dogs With Unknown Vaccination History For adult dogs with no reliable vaccination record, the AAHA guidelines recommend treating the dog as unvaccinated [2][3]. In practice this means administering a dose of the core combination vaccine, followed by a booster 2 to 4 weeks later, and then continuing on the adult 3-year schedule. A single dose in an adult dog with unknown history is not considered sufficient to guarantee protection because the dog's prior immune status is unknown. If the dog has a documented history of at least one core vaccine dose in adulthood, many veterinarians will accept a single booster and then move to the 3-year interval. The decision depends on the dog's risk profile and the veterinarian's assessment. ### Link to the Broader Puppy Schedule The DHPP series is one part of a larger puppy preventive care plan that includes deworming, fecal testing, rabies vaccination, and non-core vaccines based on lifestyle. For the full puppy timeline, see our companion guide to the [puppy vaccination schedule](/knowledge/veterinary-medicine/preventive-care/dog-vaccine-schedule). The DHPP-specific details in this article are limited to the core combination vaccine. ## Why Maternal Antibodies Drive the Puppy Series Puppies are born with an immature immune system. They receive passive immunity through colostrum, the first milk, which is rich in antibodies. These maternally derived antibodies (MDA) protect the puppy during the first weeks of life, when it cannot yet respond effectively to vaccination. The problem is that MDA cannot distinguish between a real virus and a vaccine virus. When a puppy with high MDA receives a modified-live vaccine, the maternal antibodies neutralize the vaccine before it can stimulate the puppy's own immune system. The puppy appears vaccinated but is not actually protected. Maternal antibody levels decline at different rates in different puppies. Some puppies lose MDA by 6 weeks. Others retain enough to block vaccination until 14 or 16 weeks. This variability is the reason the puppy series is repeated every 2 to 4 weeks until 16 weeks of age. Each dose is a chance to catch the puppy at the moment when MDA has fallen low enough for the vaccine to work [2]. Research into this problem is ongoing. A recombinant canine parvovirus type 2c vaccine strain has been developed that can induce immunity in puppies as young as 4 weeks of age despite high levels of maternal antibodies, which could help close the immunity gap for parvovirus [11]. This type of technology is not yet universal, but it illustrates why the timing of the puppy series matters so much. The immunity gap is also the reason a puppy should not be considered fully protected until 1 to 2 weeks after the final dose at 16 weeks or older. Until then, the puppy should be kept away from high-risk environments such as dog parks, pet stores, and areas where unknown dogs eliminate. ## Titer Testing as an Alternative to Routine Revaccination Antibody titer testing measures circulating antibodies against specific vaccine antigens. For CDV, CAV-1, and CPV-2, a protective titer correlates well with immunity. Titer testing allows veterinarians to avoid revaccinating dogs that are already protected. The AAHA guidelines recognize titer testing as a valid tool for assessing immunity to core vaccine antigens in adult dogs [2][3]. A dog with a protective titer against CDV, CAV-1, and CPV-2 does not need immediate revaccination, even if more than 3 years have passed since the last dose. Several studies support this approach. In one survey of 158 adult dogs vaccinated at least one year earlier, 84% had protective antibody titers to both CPV and CDV, 11% had borderline CPV titers, 10% had borderline CDV titers, 4% had no detectable CPV antibody, and 6% had no detectable CDV antibody [12]. Another study of 188 dogs found that 62% of dogs had positive CDV titers 5 years after their last vaccination, and 92% had positive CPV titers at the same interval [10]. Titer testing has limitations. Point-of-care tests vary in sensitivity and specificity, particularly for CDV and CAV [13]. A titer below the protective threshold does not necessarily mean the dog is unprotected, because memory B cells and cell-mediated immunity can respond rapidly to exposure even when circulating antibodies are low. Conversely, a protective titer does not guarantee that a dog will never become infected, though it strongly correlates with protection against clinical disease. For owners who want to minimize vaccination, the practical approach is to discuss titer testing with a veterinarian at the 3-year mark. If titers are protective, revaccination can be deferred. If titers are low or borderline, revaccination is the safer choice. ## Expected Mild Reactions Versus Emergencies Vaccine reactions fall into two categories: those that can be managed at home and those that require immediate veterinary attention. ### Mild Reactions (Common, Self-Limiting) Mild reactions typically appear within hours of vaccination and resolve within 24 to 48 hours. They include: - **Injection site soreness.** The dog may flinch when the area is touched or may be reluctant to move the affected limb. This usually resolves within a day. - **Lethargy.** The dog may sleep more than usual or seem less interested in activity. - **Reduced appetite.** A dog may skip one meal or eat less than usual. - **Low-grade fever.** A mild temperature elevation can occur as the immune system responds. - **Small lump at the injection site.** A soft swelling can develop under the skin. It typically resolves within a few weeks. A lump that persists beyond 3 months, grows, or becomes firm should be evaluated by a veterinarian. These reactions are signs that the immune system is responding to the vaccine. They do not require treatment in most cases. Rest and access to water are usually sufficient. If the dog is uncomfortable, a veterinarian can advise on whether an over-the-counter medication is appropriate. Do not give human medications such as acetaminophen or ibuprofen, which are toxic to dogs. ### Emergencies (Uncommon, Require Immediate Care) Serious reactions are uncommon but can occur. They include: - **Facial swelling.** Swelling around the muzzle, eyes, or ears can indicate an allergic reaction. - **Hives.** Raised, itchy welts on the skin. - **Vomiting or diarrhea.** Repeated vomiting or diarrhea within hours of vaccination can be a sign of a systemic reaction. - **Difficulty breathing.** Labored breathing, wheezing, or noisy breathing is an emergency. - **Collapse or weakness.** Sudden weakness, fainting, or inability to stand requires immediate care. - **Severe lethargy or unresponsiveness.** A dog that is difficult to rouse or does not respond to its name should be seen immediately. These signs can progress rapidly. Anaphylaxis, a severe allergic reaction, can develop within minutes to hours of vaccination. If you see any of these signs, call your veterinarian or an emergency clinic immediately. Do not wait to see if the signs resolve on their own. ### Delayed Reactions Some reactions appear days to weeks after vaccination. These include: - **Vaccine-associated adverse events** such as immune-mediated hemolytic anemia or immune-mediated thrombocytopenia. These are rare and the causal link to vaccination is often difficult to establish. - **Injection-site sarcomas.** These are rare in dogs and more commonly associated with certain feline vaccines. Any persistent lump at an injection site should be evaluated. If you notice any change in your dog's health in the weeks after vaccination, contact your veterinarian. Reporting adverse events to the manufacturer and to the USDA Center for Veterinary Biologics is part of responsible vaccine stewardship. ## Risk Factors for Adverse Reactions Not every dog reacts to vaccination, and some dogs are at higher risk. - **Previous reaction.** A dog that has reacted to a vaccine in the past is more likely to react again. Your veterinarian may pre-treat with an antihistamine or adjust the vaccine protocol. - **Small breed dogs.** Some studies suggest small breeds may be at slightly higher risk for certain reactions, though the evidence is not definitive. - **Underlying immune-mediated disease.** Dogs with a history of immune-mediated conditions may need a customized vaccination plan. - **Concurrent illness or fever.** Vaccination is generally postponed in dogs with acute illness. - **Age.** Very young puppies and very old dogs may respond differently, though the core vaccine is safe for both when administered appropriately. The AAHA guidelines emphasize that vaccination decisions should be individualized based on the dog's health status, lifestyle, and risk of exposure [2][3]. A dog that lives alone with no contact with other dogs may have a different risk profile than a dog that attends daycare or shows. ## What to Expect at the Veterinary Visit A vaccination appointment is more than an injection. It includes a physical examination, a review of the dog's history, and a discussion of risk factors. ### History and Physical Examination The veterinarian will ask about the dog's previous vaccinations, any history of reactions, current medications, and lifestyle. The physical examination checks for fever, heart murmurs, respiratory abnormalities, and other signs that might make vaccination inappropriate that day. ### Vaccine Selection The veterinarian will select the appropriate vaccine formulation. Most DHPP vaccines are modified-live virus (MLV) products. Some are recombinant. The choice depends on the dog's age, health status, and the clinic's protocols. Combination vaccines that include leptospirosis (DHLPP) are common in areas where leptospirosis is a concern. ### Administration The vaccine is typically given subcutaneously, under the skin over the shoulder or flank. Some products can be given intramuscularly. The injection is quick and most dogs tolerate it well. ### Post-Vaccination Monitoring After the injection, the dog is usually observed in the clinic for a short period to monitor for immediate reactions. Owners are advised to watch for signs of a reaction over the next 24 to 48 hours. ## Unsafe Home Remedies and Misconceptions Several myths about vaccination can lead owners to make unsafe choices. - **"I can skip the puppy series because my puppy is healthy."** Maternal antibodies do not care how healthy a puppy looks. The series is timed to overcome MDA, not to treat illness. - **"I can give the vaccine myself."** Vaccine storage, handling, and administration require proper technique. Improperly stored or administered vaccines may be ineffective. Some vaccines are only available to veterinarians. - **"Natural infection is better than vaccination."** Natural infection with distemper or parvovirus can be fatal. The risks of infection far outweigh the risks of vaccination. - **"I can use human medications for a reaction."** Human pain relievers such as ibuprofen and acetaminophen are toxic to dogs. Do not give them. - **"Titers mean I never have to vaccinate again."** Titers are a tool, not a guarantee. Some dogs lose protective titers over time. Discuss the results with your veterinarian. ## Prevention and Public Health Context The DHPP vaccine protects individual dogs and contributes to population-level immunity. Canine distemper and parvovirus are contagious and can spread rapidly in unvaccinated populations. Outbreaks occur in shelters, breeding kennels, and areas with low vaccination rates. The AAHA guidelines note that vaccination is a cornerstone of canine preventive healthcare and one of the most cost-effective ways of maintaining a dog's health, longevity, and quality of life [2][3]. The guidelines also address the role of vaccination in shelters, where infectious disease control is a constant challenge. Rabies vaccination is separate from DHPP and is required by law in most US states. The rabies vaccine is often given at the same visit as the DHPP vaccine, and studies have shown that the two vaccines do not interfere with each other when given concurrently at separate sites [8][14]. ## Limitations and When to Contact a Veterinarian This article provides general information about the DHPP vaccine. It cannot replace an individual assessment by a veterinarian who knows your dog's health history, lifestyle, and risk factors. Contact a veterinarian promptly if: - Your dog has facial swelling, hives, vomiting, diarrhea, difficulty breathing, or collapse after vaccination. - Your dog has a lump at the injection site that persists for more than 3 months, grows, or becomes firm. - Your dog has a known history of vaccine reaction and is due for a booster. - Your puppy is older than 16 weeks and has never been vaccinated. - You have an adult dog with an unknown vaccination history. - You want to discuss titer testing instead of routine revaccination. - Your dog is pregnant, nursing, or has an immune-mediated disease. - Your dog is due for vaccination but is currently ill or on medication. Vaccination decisions should be made with a veterinarian who can weigh the benefits of protection against the small risk of adverse effects. ## Frequently Asked Questions ### What does the DHPP vaccine protect against? The DHPP vaccine protects against four diseases: canine distemper virus, canine adenovirus (infectious hepatitis), canine parvovirus, and canine parainfluenza virus. These are the core vaccine antigens recommended by the AAHA for all dogs [2][3]. ### Is the DHPP vaccine the same as the 5 in 1 vaccine for dogs? The 5 in 1 vaccine for dogs typically refers to the four core antigens plus a leptospirosis component. The DHPP vaccine without leptospirosis covers four diseases. The DHLPP vaccine covers five. The naming depends on whether leptospirosis is included. ### How often does my dog need the DHPP vaccine? Puppies receive a series of doses every 2 to 4 weeks until they are at least 16 weeks old, followed by a booster within one year. After that, immunocompetent adult dogs are revaccinated no more often than every 3 years [2][3][9]. ### What is the difference between DHPP and DA2PP? DHPP and DA2PP refer to the same vaccine. The "H" stands for hepatitis, which is caused by canine adenovirus type 1. The "A2" specifies canine adenovirus type 2, the strain used in the vaccine. Both abbreviations describe the same four core antigens [1]. ### Can my dog have a reaction to the DHPP vaccine? Mild reactions such as soreness, lethargy, and reduced appetite are common and resolve within 24 to 48 hours. Serious reactions such as facial swelling, hives, vomiting, or difficulty breathing are uncommon but require immediate veterinary care. ### Can I use titer testing instead of vaccinating every 3 years? Titer testing can be used to assess immunity to CDV, CAV-1, and CPV-2 in adult dogs. If titers are protective, revaccination can be deferred. The AAHA guidelines recognize titer testing as a valid tool for adult dogs [2][3]. Discuss the results with your veterinarian. ### What should I do if my adult dog has never been vaccinated? Adult dogs with no vaccination history should be treated as unvaccinated. The AAHA guidelines recommend an initial dose followed by a booster 2 to 4 weeks later, then the standard adult 3-year schedule [2][3]. ### Is the DHPP vaccine safe for pregnant dogs? Modified-live vaccines are generally not recommended for pregnant dogs. Discuss vaccination timing with your veterinarian if your dog is pregnant or you are planning a breeding. ## Related Articles - [Lyme Vaccine for Dogs: Tick Protection Efficacy and Side Effects Debate](/knowledge/veterinary-medicine/preventive-care/lyme-vaccine-for-dogs-tick-protection-efficacy-and-side-effects-debate) - [Dog Vaccine Schedule](/knowledge/veterinary-medicine/preventive-care/dog-vaccine-schedule) - [What Are the Side Effects of Clavamox for Dogs?](/knowledge/veterinary-medicine/pet-medication-guide/clavamox-side-effects-dogs) - [What Are the Side Effects of Gabapentin for Dogs?](/knowledge/veterinary-medicine/pet-medication-guide/gabapentin-side-effects-dogs) - [What Are the Side Effects of Vetmedin for Dogs?](/knowledge/veterinary-medicine/pet-medication-guide/vetmedin-side-effects-dogs) - [What Are the Side Effects of Prednisone in Dogs?](/knowledge/veterinary-medicine/pet-medication-guide/prednisone-side-effects-dogs) ## Sources 1. [Three-year duration of immunity in dogs following vaccination against canine adenovirus type-1, canine parvovirus, and canine distemper virus.](https://pubmed.ncbi.nlm.nih.gov/15906266/) 2. [2022 AAHA Canine Vaccination Guidelines (2024 Update).](https://pubmed.ncbi.nlm.nih.gov/39480742/) 3. [2022 AAHA Canine Vaccination Guidelines.](https://pubmed.ncbi.nlm.nih.gov/36049241/) 4. [Evaluation of the efficacy and duration of immunity of a canine combination vaccine against virulent parvovirus, infectious canine hepatitis virus, and distemper virus experimental challenges.](https://pubmed.ncbi.nlm.nih.gov/15578450/) 5. [Decoding canine parvovirus: biomarkers for diagnosis and advances in vaccine development to address emerging challenges.](https://pubmed.ncbi.nlm.nih.gov/40843250/) 6. [Three-year serologic immunity against canine parvovirus type 2 and canine adenovirus type 2 in dogs vaccinated with a canine combination vaccine.](https://pubmed.ncbi.nlm.nih.gov/18183549/) 7. [Duration of serological response to canine parvovirus-type 2, canine distemper virus, canine adenovirus type 1 and canine parainfluenza virus in client-owned dogs in Australia.](https://pubmed.ncbi.nlm.nih.gov/23186088/) 8. [Three-year rabies duration of immunity in dogs following vaccination with a core combination vaccine against canine distemper virus, canine adenovirus type-1, canine parvovirus, and rabies virus.](https://pubmed.ncbi.nlm.nih.gov/17039445/) 9. [Duration of immunity for canine and feline vaccines: a review.](https://pubmed.ncbi.nlm.nih.gov/16707236/) 10. [Influence of age and vaccination interval on canine parvovirus, distemper virus, and adenovirus serum antibody titers.](https://pubmed.ncbi.nlm.nih.gov/37418822/) 11. [Development of a Novel Canine Parvovirus Vaccine Capable of Stimulating Protective Immunity in Four-Week-Old Puppies in the Face of High Levels of Maternal Antibodies.](https://pubmed.ncbi.nlm.nih.gov/37766175/) 12. [Application of a dot enzyme-linked immunosorbent assay for evaluation of the immune status to canine parvovirus and distemper virus in adult dogs before revaccination.](https://pubmed.ncbi.nlm.nih.gov/16789715/) 13. [Antibody Titer Testing in Dogs: Evaluation of Three Point-of-Care Tests for Canine Core Vaccine Antigens Compared to Virus Neutralization.](https://pubmed.ncbi.nlm.nih.gov/40872688/) 14. [Compatibility between a rabies vaccine and two canine combined vaccines against canine distemper, adenovirosis, parvovirosis, parainfluenza virus disease and leptospirosis, with or without canine coronavirus.](https://pubmed.ncbi.nlm.nih.gov/35429805/)