RESULTS OF PROPHYLACTIC INOCULATION AGAINST PNEUMOCOCCUS IN 12,519 MEN

The remarkable history of pneumococcal vaccination: an ongoing challenge

Although it varies with age and geographical distribution, the global burden of infection with Streptococcus pneumoniae (pneumococcus) remains considerable. The elderly, and younger adults with comorbid conditions, are at particularly high risk of pneumococcal infection, and this risk will increase as the population ages. Vaccination should be the backbone of our current strategies to deal with this infection.

Main body: This manuscript reviews the history of the development of pneumococcal vaccines, and the impact of different vaccines and vaccination strategies over the past 111 years. It documents the early years of vaccine development in the gold mines of South Africa, when vaccination with killed pneumococci was shown to be effective, even before the recognition that different pneumococci were antigenically distinct. The development of type-specific vaccines, still with whole killed pneumococci, showed a high degree of efficacy. The identification of the importance of the pneumococcal capsule heralded the era of vaccination with capsular polysaccharides, although with the advent of penicillin, interest in pneumococcal vaccine development waned. The efforts of Austrian and his colleagues, who documented that despite penicillin therapy, patients still died from pneumococcal infection in the first 96 h, ultimately led to the licensing first of a 14-valent pneumococcal polysaccharide in 1977 followed by the 23-valent pneumococcal polysaccharide in 1983. The principal problem with these, as with other polysaccharide vaccines, was that that they failed to immunize infants and toddlers, who were at highest risk for pneumococcal disease. This was overcome by chemical linking or conjugation of the polysaccharide molecules to an immunogenic carrier protein. Thus began the era of pneumococcal conjugate vaccine (PCV), starting with PCV7, progressing to PCV10 and PCV13, and, most recently, PCV15 and PCV20. However, these vaccines remain serotype specific, posing the challenge of new serotypes replacing vaccine types. Current research addresses serotype-independent vaccines which, so far, has been a challenging and elusive endeavor.

Conclusion: While there has been enormous progress in the development of pneumococcal vaccines during the past century, attempts to develop a vaccine that will retain its efficacy for most pneumococcal serotypes are ongoing.

A century of pneumococcal vaccination research in humans

Sir Almroth Wright coordinated the first trial of a whole-cell pneumococcal vaccine in South Africa from 1911 to 1912. Wright started a chain of events that delivered pneumococcal vaccines of increasing clinical and public-health value, as medicine advanced from a vague understanding of the germ theory of disease to today's rational vaccine design. Early whole-cell pneumococcal vaccines mimicked early typhoid vaccines, as early pneumococcal antisera mimicked the first diphtheria antitoxins. Pneumococcal typing systems developed by Franz Neufeld and others led to serotype-specific whole-cell vaccines. Pivotally, Alphonse Dochez and Oswald Avery isolated pneumococcal capsular polysaccharides in 1916-17. Serial refinements permitted Colin MacLeod and Michael Heidelberger to conduct a 1944-45 clinical trial of quadrivalent pneumococcal polysaccharide vaccine (PPV), demonstrating a high degree of efficacy in soldiers against pneumococcal pneumonia. Two hexavalent PPVs were licensed in 1947, but were little used as clinicians preferred therapy with new antibiotics, rather than pneumococcal disease prevention. Robert Austrian's recognition of high pneumococcal case-fatality rates, even with antibiotic therapy, led to additional trials in South Africa, the USA and Papua New Guinea, with 14-valent and 23-valent PPVs licensed in 1977 and 1983 for adults and older children. Conjugation of polysaccharides to proteins led to several pneumococcal conjugate vaccines licensed since 2000, enabling immunization of infants and young children and resultant herd protection for all ages. Today, emergence of disease caused by pneumococcal serotypes not included in various vaccine formulations fuels research into conserved proteins or other means to maximize protection against more than 90 known pneumococcal serotypes.

RESULTS OF PROPHYLACTIC VACCINATION AGAINST PNEUMONIA AT CAMP WHEELER

1. 13,460 men, or about 80 per cent of the entire camp strength, were vaccinated against pneumonia with pneumococcus lipovaccine. 2. The dosage employed in all cases was 1 cc. of the lipovaccine containing approximately 10 billion each of Pneumococcus Types I, II, and III. 3. Both the local and general reactions produced by the vaccine were usually mild. Only 0.7 per cent of those who received the vaccine were sufficiently affected to need hospital care. None of these was seriously ill, and a majority of them returned to duty on the 2nd or 3rd day after admission. 4. Most of the troops inoculated were under observation for 2 or 3 months after vaccination. During this period there were 32 cases of Pneumococcus Type I, II, and III pneumonia among the vaccinated four-fifths of camp, and 42 cases of pneumonia of these types among the unvaccinated one-fifth of camp. If, however, all cases of pneumonia that developed within 1 week after vaccination are excluded from the vaccinated group, there remain only 8 cases of pneumonia produced by fixed types, and these were all secondary to severe attacks of influenza. This exclusion is justified by the fact that protective bodies do not begin to appear in the serum until the 8th day after injection of pneumococcus lipovaccine. 5. There is no evidence whatever that pneumococcus vaccine predisposes the individual even temporarily toward either pneumococcus or streptococcus pneumonia. 6. The weekly incidence rate for pneumonia (all types) among the vaccinated troops was conspicuously lower than that for the unvaccinated troops. 7. The pneumonia incidence rate per 1,000 men during the period of the experiment was twice as high for unvaccinated recruits as for vaccinated recruits, and nearly seven times as high for unvaccinated seasoned men as for vaccinated seasoned men. 8. Influenza causes a marked reduction in resistance to pneumonia even among vaccinated men. Of the 155 cases of pneumonia (all types) developing 1 week or more after vaccination, 133 were secondary to influenza. 9. The death rate for 155 cases of pneumonia (all types) that developed among vaccinated men 1 week or more after vaccination was only 12.2 per cent, whereas the death rate for 327 cases of all types that occurred among unvaccinated troops was 22.3 per cent. The death rate for primary pneumonia among vaccinated troops was 11.9 per cent. Among unvaccinated, it was 31.8 per cent, almost three times as great. On the other hand, the mortality rate in pneumonia secondary to influenza is about the same for the vaccinated and unvaccinated groups. 10. In conclusion, it must be admitted that the results of pneurnococcus vaccination at Camp Wheeler have not been so striking as those obtained at Camp Upton in 1918, largely on account of the influenza epidemic; but, although influenza obscured to some extent the effect of pneumococcus vaccination at Camp Wheeler, the results are sufficiently encouraging to justify its further application in civil as well as in military life.

ANTIPNEUMOCOCCIC IMMUNITY REACTIONS IN INDIVIDUALS OF DIFFERENT AGES

1. The incidence of pneumococcidal power of the whole defibrinated blood in human beings has been shown to vary with age. The age distribution of other type-specific antibodies varies similarly, insofar as they are frequent enough to be compared or technically demonstrable. 2. The incidence of pneumococcidal power of the whole defibrinated blood for Type I, Type II, and Type III differs. Type I is the rarest, Type II is the most frequent, and Type III is of intermediate frequency. The type-specific antibodies responsible for the other tests employed show a similar relative frequency in regard to Types I and II, but some variation in regard to Type III. 3. The skin reactions to the acetic acid-predpitable proteins and autolysates of the pneumococci are negative or rarely positive in infants, infrequently positive in childhood, and positive in a high percentage of adults.

FURTHER EXPERIMENTS WITH THE INTRADERMAL PNEUMOCOCCUS INFECTION IN RABBITS

1. The continuation of our experiments with intradermal Type I pneumococcus infection in rabbits has furnished further evidence of the marked analogies between this condition and that of human lobar pneumonia. 2. It has been found that the amount of antiserum necessary for successful therapy increases as the disease progresses, and that this progression has a definite mathematical character. Such a condition, it seems, can only be caused by a progressive accumulation of some toxic or antagonistic substance, the exact nature of which is not known. 3. Various lots of antipneumococcus sera have been tested for their therapeutic properties. The results from seven such sera show that this therapeutic value does not parallel the mouse-protective value. It is suggested that the rabbit technic may prove useful for the routine comparison and standardization of antipneumococcus sera since it represents a simple method for determining that property for which the serum is to be utilized. 4. The effect of non-specific therapy in this condition has been determined to be a transient disappearance from the blood stream of circulating organisms. This result was obtained with such heterologous materials as normal horse serum and typhoid vaccine but not with the homologous normal rabbit serum. 5. Rabbits recovering from the intradermal disease without treatment or with such inadequate treatment that the disease runs its normal course, were shown to have a definite though not permanent immunity. Cases in which the disease had been arrested at 24 hours by effective therapy with heterologous immune serum showed no immunity after the early disappearance of the passively administered elements. Cases which were brought to early recovery with immune homologous serum did show a definite immunity comparable to that which was developed in other animals as the result of an untreated course of the disease. 6. The immunity conferred by single and multiple vaccination is reported. The possibility of the application of such methods in the pneumonias of man is discussed and a method for such an application is suggested.

FACTORS INVOLVED IN THE PRODUCTION OF IMMUNITY WITH PNEUMOCOCCUS VACCINE : II. INDUCTION OF ACTIVE IMMUNITY DURING THE COURSE OF LOBAR PNEUMONIA

1. Pneumococcus vaccine was administered to 29 patients with pneumonia to determine whether a state of immunity could be induced during the course of the disease. Twenty patients received an intravenous injection of pneumococcus vaccine or pneumococcus filtrate. Nine pneumonia patients received an intradermal injection of vaccine. Eight patients with miscellaneous disease received an intravenous or intradermal injection of pneumococcus vaccine. 2. Of 23 tests in which the serum of the patient was studied for the appearance of protective substance after intravenous injection of heterologous pneumococcus vaccine, 20 or 87 per cent showed a positive response within 6 days after the administration of the antigen. The average day of onset was 4.4 days after injection. 3. Of 9 tests of the same character following the intravenous injection of pneumococcus filtrate, 8 or 89 per cent showed a positive response. The average day of onset of protective substance was 5.6 days after injection. 4. The appearance of specific protective substance following heterologous injection of pneumococcus vaccine appeared to be due to the introduction of the vaccine and not to the natural course of the disease, as was shown by negative control experiments. 5. Of 24 tests with intradermal injection of vaccine, 10 or 42 per cent developed slight protective substance of irregular degree 4.5 days after injection. 6. No immediate reactions were observed following the intravenous or intradermal injection of pneumococcus vaccine. One chill occurred after injection of pneumococcus filtrate. Of 20 cases with intravenous injection of pneumococcus vaccine or filtrate, 2 died of their disease, one a case in which homologous vaccine was used and one in which heterologous vaccine was administered. 7. Conclusions concerning the therapeutic value of the introduction of pneumococcus vaccine in pneumonia must await further investigation. These studies demonstrate that specific protective substances generally appear 4 to 5 days after intravenous injection of pneumococcus vaccine during the course of lobar or bronchopneumonia.

STUDIES ON PNEUMOCOCCUS GROWTH INHIBITION : VII. THE RELATION OF OPSONINS TO NATURAL RESISTANCE AGAINST PNEUMOCOCCUS INFECTION

A study was made of the pneumococcidal action of serum-leucocyte mixtures of pneumococcus-resistant animals with a view to determining whether this property of the blood is to be accounted for by the presence of certain serum constituents or by cellular characteristics which are lacking in the blood of susceptible animals. By means of a method specially developed for this purpose, it was found that, after adequate contact with the serum of pneumococcus-resistant animals, virulent pneumococci were phagocyted actively not only by the homologous leucocytes but also by the leucocytes of other resistant and susceptible animals. On the other hand, pneumococci exposed to the action of the serum of pneumococcus-susceptible animals were not taken up by the leucocytes of either the resistant or susceptible species. All the resistant animals tested, dog, cat, sheep, pig and horse, showed marked opsonic properties in their blood serum which were not found in the serum of susceptible ones, rabbit, guinea pig and human. There appeared, however, to be no essential difference in the phagocytic activity of the leucocytes from the various animals. It was then shown that the pneumococcus-destroying power of serum-leucocyte mixtures was entirely abolished when heated serum was substituted for fresh serum and that such heated serum had lost much of its opsonic potency. Neither the living leucocytes alone nor extracts of the leucocytes were observed to exert any killing action on pneumococci. Further evidence of the controlling influence of opsonic action in the antipneumococcus defence mechanism of the blood, and its importance in natural resistance, was afforded by a study of the opsonin content and leucocytic functions of the blood of full grown and young rabbits as related to their widely varying degrees of pneumococcus susceptibility.

Pneumococcal vaccination: work to date and future prospects

In our opinion, the conclusion from all these studies is that pneumococcal polysaccharides in the form in which they have been administered are relatively poor immunogens when compared, for example, to certain proteins such as tetanus toxoid. Had pneumococcal vaccination been the success that might reasonably have been predicted, there would be no argument, this many years later, over its merits. Although polysaccharide vaccines appear to have been effective in mass vaccination programs and in epidemic situations where presumably healthy adults have been involved, it has been more difficult to document their efficacy in individuals who are most in need of them, namely those with aberrant or senescent immune systems. There seems to be no disagreement that antibody at some concentration (the precise level remains to be determined) will, in general, be associated with protection, although in any one individual, for a variety of reasons, infection with a vaccine serotype might still occur. Thus, the clear direction for the future should be not to argue further the merits of currently available vaccine preparations, but rather to work rapidly and efficiently to develop and test new and more effective polysaccharide antigens. Studies in the past 10 years have shown that the polyribosyl ribitolphosphate (PRP) of Haemophilus influenzae type b is a far more effective antigen when conjugated to diphtheria toxoid. For example, in a study in our laboratory, vaccination of healthy young adults with PRP-conjugated diphtheria toxoid yielded serum antibody levels 10- to 100-fold higher than after PRP alone. Responses may be even better if other proteins are used.(ABSTRACT TRUNCATED AT 250 WORDS)