Im­mu­nity con­ferred in many ways and some­times not at all

Prince Albert Daily Herald - - OPINION - Keith Roach

(There are se­ri­ous com­pli­ca­tions of the dis­ease, which is why it’s much bet­ter to get the vac­cine.) How­ever, most peo­ple will never get nat­u­ral im­mu­nity from malaria, even after heavy ex­po­sure and nu­mer­ous bouts of the dis­ease.

Some dis­eases, like in­fluenza, are con­stantly chang­ing, re­quir­ing new vac­cines ev­ery year. It’s a chal­lenge for im­mu­nol­o­gists to cre­ate ef­fec­tive vac­cines, but re­searchers con­tinue to make progress.

In the case of per­tus­sis (whoop­ing cough), in­fec­tion does not pre­vent re­cur­rences. In the pre-vac­cine era, nearly ev­ery­one had per­tus­sis as a child, and it is es­ti­mated that an adult had per­tus­sis be­tween two and three times in a life­time. Also in the pre-vac­cine era, there were about 9,000 deaths per year from per­tus­sis, com­pared with about 20 deaths per year now. Even though im­mu­nity from the cur­rent per­tus­sis vac­cine does wane, booster doses are not cur­rently rec­om­mended.

In the case of tetanus, sur­viv­ing the in­fec­tion (even now, 10 to 20 per­cent of those in­fected with tetanus die) does not con­fer im­mu­nity. Sur­vivors should be im­mu­nized as soon as the con­di­tion sta­bi­lizes. A full se­ries of tetanus vac­cines gives nearly 100 per­cent pro­tec­tion, which is why tetanus is called “the un­for­giv­able dis­ease”: No­body should get it, and if the omis­sion of the vac­cine was the physi­cian’s fault, he or she can’t be for­given for it.

The mech­a­nisms by which in­fec­tions es­cape our im­mune sys­tem are com­pli­cated: Over mil­lions of years, hu­mans have evolved to be bet­ter at fight­ing off in­fec­tions, but in­fec­tions have been learn­ing to evade our de­fenses.

DEAR DR. ROACH: In a re­cent col­umn, you said that “cur­rent or for­mer smok­ers should not take the stan­dard sup­ple­ment, as it con­tains beta carotene, which may in­crease lung can­cer risk.” By “stan­dard sup­ple­ment,” are you re­fer­ring to AREDS? Also, I have never heard that smok­ers or for­mer smok­ers should not take beta carotene. Why? I have not smoked in over 30 years. Would this af­fect me? -- V.W.

AN­SWER: Two large stud­ies showed the ben­e­fit of vi­ta­min sup­ple­men­ta­tion in slow­ing the pro­gres­sion of mac­u­lar de­gen­er­a­tion. The first one, the AREDS, used a com­bi­na­tion of vi­ta­mins, in­clud­ing beta carotene. The sec­ond, AREDS2, did not.

A dif­fer­ent study, de­signed to de­ter­mine whether vi­ta­min sup­ple­ments help to pre­vent smok­ers from get­ting lung can­cer, found that ac­tive smok­ers tak­ing beta carotene were more likely to get lung can­cer. That study had some method­olog­i­cal weak­nesses, but most ex­perts rec­om­mend against cur­rent smok­ers tak­ing a sup­ple­ment with beta carotene. That’s why I rec­om­mend that peo­ple with mac­u­lar de­gen­er­a­tion use the AREDS2 for­mu­la­tion, which is ap­pro­pri­ate for both smok­ers and non­smok­ers. I would rec­om­mend that for­mer smok­ers use the AREDS2 for­mu­la­tion, based only on min­i­miz­ing risk.

Please note that foods high in beta carotene are still thought to be help­ful in re­duc­ing risk for many con­di­tions, in­clud­ing heart dis­ease and sev­eral can­cers, for smok­ers and for non­smok­ers (but quit­ting is the best way to re­duce can­cer risk).

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